ISO 24687:2023

Fine ceramics (advanced ceramics, advanced technical ceramics) — Measurement of Seebeck coefficient and electrical conductivity of bulk-type thermoelectric materials at room and high temperatures

This document specifies the measurement methods for the electronic transport properties of bulk-type thermoelectric materials at room and elevated temperatures. The measurement methods cover the simultaneous determination of Seebeck coefficient and electrical conductivity of bulk-type thermoelectric materials in a temperature range from 300 K to 1 200 K. The measurement methods are applicable to bulk-type thermoelectric materials used for power generation, energy harvesting, cooling and heating, among other things.

Céramiques techniques — Mesurage du coefficient de Seebeck et de la conductivité électrique de matériaux thermoélectriques en vrac à température ambiante et à haute température

General Information

• Status: Published
• Publication Date: 19-Apr-2023
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: ISO/TC 206 - Fine ceramics
• Drafting Committee: ISO/TC 206/WG 11 - Electrical and optical applications
• Current Stage: 6060 - International Standard published
• Start Date: 20-Apr-2023
• Due Date: 17-Aug-2023
• Completion Date: 20-Apr-2023

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 24687
First edition
2023-04
Fine ceramics (advanced ceramics,
advanced technical ceramics) —
Measurement of Seebeck coefficient
and electrical conductivity of bulk-
type thermoelectric materials at room
and high temperatures
Céramiques techniques — Mesurage du coefficient de Seebeck et de
la conductivité électrique de matériaux thermoélectriques en vrac à
température ambiante et à haute température
Reference number
ISO 24687:2023(E)
© ISO 2023

---------------------- Page: 1 ----------------------
ISO 24687:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2023 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 24687:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Significance and use .4
6 Apparatus . 4
7 Sampling . 5
7.1 Shape and dimension of specimen . 5
7.2 Pre-treatment . 6
7.3 Storage . 6
7.4 Number of specimens . 6
8 Procedure .6
8.1 Dimension measurement of specimen . 6
8.2 Placement of specimen . 6
8.3 Evacuating and purging the chamber . 7
8.4 Measurement of electrical conductivity . 7
8.5 Measurement of Seebeck coefficient . 7
9 Calculation . 7
9.1 Seebeck coefficient. 7
9.2 Electrical conductivity . 9
10 Expression of results .10
10.1 Seebeck coefficient and electrical conductivity . 10
10.2 Variation of Seebeck coefficient as a function of temperature . 11
10.3 Variation of electrical conductivity as a function of temperature . 11
11 Test report .12
Annex A (informative) Interlaboratory evaluation of Seebeck coefficient and electrical
conductivity of bulk-type thermoelectric materials .14
Annex B (informative) Periodic check of the apparatus (or equipment) by using a certified
reference material (CRM) or a reference material (RM) .20
Bibliography .21
iii
© ISO 2023 – All rights reserved

---------------------- Page: 3 ----------------------
ISO 24687:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2023 – All rights reserved

---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 24687:2023(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Measurement of Seebeck coefficient and
electrical conductivity of bulk-type thermoelectric
materials at room and high temperatures
1 Scope
This document specifies the measurement methods for the electronic transport properties of bulk-
type thermoelectric materials at room and elevated temperatures. The measurement methods
cover the simultaneous determination of Seebeck coefficient and electrical conductivity of bulk-type
thermoelectric materials in a temperature range from 300 K to 1 200 K. The measurement methods are
applicable to bulk-type thermoelectric materials used for power generation, energy harvesting, cooling
and heating, among other things.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 23331, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for total
electrical conductivity of conductive fine ceramics
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
thermoelectric figure of merit
zT
dimensionless factor representing the thermoelectric conversion efficiency of a given material
3.2
thermoelectric power factor
2
S σ
characteristic value of a thermoelectric material given by the product of the square of Seebeck
coefficient (S) and electrical conductivity (σ)
2
Note 1 to entry: The units of the thermoelectric power factor are watts per metre per square kelvin (W/mK ).
1
© ISO 2023 – All rights reserved

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ISO 24687:2023(E)
3.3
Seebeck coefficient
S
intrinsic property which describes the induced voltage (thermal electromotive force, E) from a given
temperature difference (∆T) in a material
Note 1 to entry: The units of the Seebeck coefficient are microvolts per kelvin (μV/K).
3.4
electrical conductivity
σ
ability of a material to allow the transport of electric charges
Note 1 to entry: The units of electrical conductivity are Siemens per centimetre (S/cm).
4 Principle
This document is for simultaneously measuring the Seebeck coefficient and the electrical conductivity of
bulk-type thermoelectric materials using one measurement system. The off-axis four-terminal method
can be used to simultaneously measure the Seebeck coefficient and the electrical conductivity of bulk-
type thermoelectric material using one measurement system. As shown in Figure 1, the specimen is
set between two metal blocks in the heating zone and two thermocouple probes separately contact
the surface of the specimen. The measurement of the Seebeck coefficient of a bulk-type thermoelectric
material is necessary to measure the temperature difference between two positions (point H and
point C) on a specimen and the voltage across the two same positions (Figure 1). Seebeck coefficient
can be calculated by following Formula (1):
SE= /ΔT (1)
where
E is the induced thermoelectric voltage (thermal electromotive force) between the point H and
point C of the specimen;
∆T is the temperature difference between the point H and point C (= T - T ).
H C
For Seebeck coefficient measurement, measured temperature is the average temperature of the hot-
and cold-side thermocouple probes.
By using the measuring system illustrated in Figure 2, electrical conductivity is also measured based
on the four-terminal method. This method is conducted by placing four probes. Constant current is
applied through the two outmost probes, causing a measurable voltage drop, V, between the two inner
probes. The electrical resistance, R, is calculated using Ohm’s law following Formula (2):
RV= /I (2)
where
V is the voltage;
I is the current.
The resistivity, ρ, is be calculated following Formula (3):
ρ=RA /l (3)
2
  © ISO 2023 – All rights reserved

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ISO 24687:2023(E)
where
A is the cross-sectional area of the specimen;
l is the separation between the two inner probes.
The electrical conductivity is the reciprocal of the resistivity. For electrical conductivity measurement,
measured temperature is the actual temperature of the specimen, which generally can be measured by
furnace temperature.
Key
1 upper metal block 2 specimen
3 lower metal block 4 heater
5 point C 6 point H
7 upper thermocouple probe (cold side) 8 lower thermocouple probe (hot side)
9 current electrode 10 heating furnace
Figure 1 — Schematic diagram of off-axis four-terminal method for simultaneous measurement
of Seebeck coefficient and electrical conductivity
3
© ISO 2023 – All rights reserved

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ISO 24687:2023(E)
Key
1 inner probes 2 outer probes
3 specimen 4 electrodes
Figure 2 — Schematic diagram of four-terminal method to measure the electrical resistivity
The results of an interlaboratory test are given in Annex A.
5 Significance and use
This document gives guidance for simultaneously measuring the high-accuracy and low-error Seebeck
coefficient and electrical conductivity of thermoelectric materials. Therefore, this standard is intended
to be used for the development, characterization and quality control of thermoelectric materials, data
acquisition for high-efficiency thermoelectric system design, etc.
Thermoelectric materials show Seebeck effect, Peltier effect and Thomson effect. The Seebeck effect is
the direct conversion of heat into electricity. The conversion efficiency of a thermoelectric material is
determined by the dimensionless thermoelectric figure of merit, zT, calculated following Formula (4):
2
zT =STσκ/ (4)
where
S is the Seebeck coefficient;
σ is the electrical conductivity;
κ is the thermal conductivity;
T is the absolute temperature.
Thermoelectric materials show a trade-off relation between Seebeck coefficient and electrical
2
conductivity according to carrier concentration. Therefore, the accuracy of the power factor, S σ, where
S is the Seebeck coefficient and σ is the electrical conductivity, can be improved through simultaneous
measurement of Seebeck coefficient and electrical conductivity in one run.
6 Apparatus
6.1 Current source, accurate to ±0,5 % on ranges of −1 A to +1 A used in the measurement.
4
  © ISO 2023 – All rights reserved

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ISO 24687:2023(E)
−7
6.2 Electronic voltmeter, at least capable of measuring potential differences from 10 V to 0,05 V
-7
with a resolution below 10 V.
6.3 Conducting metal blocks.
The contact surface of conducting metal blocks shall be sufficiently large compared to a measurement
specimen. A specimen shall be placed between two conducting metal blocks, such as platinum or
tungsten. One end of the specimen is heated while the other acts as a heat sink, dispersing heat, thus
cooling that side. In addition, the conducting metal blocks play a role as the electrodes for applying the
current when measuring the electrical conductivity.
NOTE Pt or Pt – Pd alloy is the best electrode material due to high measuring temperatures.
6.4 Thermocouple probes.
The diameter of thermocouple probes shall be 0,5 mm or less to obtain reproducible Seebeck
coefficient value. Thermocouples should have a resolution of at least 0,01 K or better. Thermocouple
probes integrating electrical probes for measuring the voltage and thermal probes for measuring the
temperature should be designed for working from 300 K to 1 200 K. Thermocouple probes should be
checked periodically as their output may drift with usage or contamination.
NOTE In some equipment, the voltage can be measured only with thermocouple wires without additional
electrical probes.
6.5 Test chamber.
The test chamber shall be capable of heating both the specimen and the conducting metal blocks up
to at least 1 200 K as well as maintaining the test temperature within ±1 K during the test, by which
vacuum environment shall be available for test requirement. The test chamber should be evacuated
below 3 Pa and can be backfilled with a variety of gases such as helium, argon, nitrogen and oxygen or a
mixture of these. Low-pressure helium can be used to improve the thermal contact between the probe
and the sample. However, low pressure may affect the m
...

2022-12-08
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line: 0 pt, Tab stops: Not at 21.6 pt
ISO/FDIS 24687:20222023(E)
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Not at 18 pt
DATE: 2023-xx
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ISO TC 206/WG 11
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Secretariat: JISC
Style Definition: Heading 6: Font: Bold
Style Definition: ANNEX
Style Definition: AMEND Terms Heading: Font: Bold
Style Definition: AMEND Heading 1 Unnumbered:
Font: Bold
Fine ceramics (advanced ceramics, advanced technical ceramics) — Measurement of
Seebeck coefficient and electrical conductivity of bulk-type thermoelectric materials at Formatted: Justified
room and high temperatures
Céramiques techniques — Mesurage du coefficient de Seebeck et de la conductivité électrique de
matériaux thermoélectriques de base à températures ambiante et élevée

---------------------- Page: 1 ----------------------
ISO/FDIS 24687:20222023(E)
© ISO 20222023, Published in Switzerland
Commented [A1]: The reference is to a withdrawn
standard which has been replaced

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or
ISO/IEC 2022, Information technology — Character code
utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or
structure and extension techniques
posting on the internet or an intranet, without prior written permission. Permission can be requested
Formatted: Pattern: Clear
from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
[e-mail]
www.iso.org
www.iso.org
ii © ISO 20222023 – All rights reserved

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ISO/FDIS 24687:20222023(E)
Contents
Foreword . Error! Bookmark not defined.
1 Scope . Error! Bookmark not defined.
2 Normative references . Error! Bookmark not defined.
3 Terms and definitions . Error! Bookmark not defined.
4 Principle . Error! Bookmark not defined.
5 Significance and use . Error! Bookmark not defined.
6 Apparatus . Error! Bookmark not defined.
6.1 Current source . Error! Bookmark not defined.
6.2 Electronic voltmeter . Error! Bookmark not defined.
6.3 Conducting metal blocks . Error! Bookmark not defined.
6.4 Thermocouple probes . Error! Bookmark not defined.
6.5 Test chamber . Error! Bookmark not defined.
6.6 Dimension-measuring device . Error! Bookmark not defined.
6.7 Periodic check of apparatus and equipment . Error! Bookmark not defined.
7 Sampling . Error! Bookmark not defined.
7.1 Shape and dimension of specimen . Error! Bookmark not defined.
7.2 Pre-treatment . Error! Bookmark not defined.
7.3 Storage . Error! Bookmark not defined.
7.4 Number of specimens . Error! Bookmark not defined.
8 Procedure . Error! Bookmark not defined.
8.1 Dimension measurement of specimen . Error! Bookmark not defined.
8.2 Placement of specimen . Error! Bookmark not defined.
8.3 Evacuating and purging the chamber . Error! Bookmark not defined.
8.4 Measurement of electrical conductivity . Error! Bookmark not defined.
8.5 Measurement of Seebeck coefficient . Error! Bookmark not defined.
9 Calculation . Error! Bookmark not defined.
9.1 Seebeck coefficient . Error! Bookmark not defined.
9.2 Electrical conductivity . Error! Bookmark not defined.
10 Expression of results . Error! Bookmark not defined.
10.1 Seebeck coefficient and electrical conductivity . Error! Bookmark not defined.
10.2 Variation of Seebeck coefficient as a function of temperature . Error! Bookmark not
defined.
10.3 Variation of electrical conductivity as a function of temperature . Error! Bookmark not
defined.
11 Test report . Error! Bookmark not defined.
Annex A (informative) Interlaboratory evaluation of Seebeck coefficient and electrical
conductivity of bulk-type thermoelectric materials . Error! Bookmark not defined.
A.1 General . Error! Bookmark not defined.
A.2 Sample . Error! Bookmark not defined.
© ISO 20222023 – All rights reserved iii

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ISO/FDIS 24687:20222023(E)
A.2.1 Material . Error! Bookmark not defined.
A.2.2 Material dimension . Error! Bookmark not defined.
A.3 Test conditions . Error! Bookmark not defined.
A.3.1 Temperature range. Error! Bookmark not defined.
A.3.2 Method . Error! Bookmark not defined.
A.3.3 Environment . Error! Bookmark not defined.
A.4 Laboratories participating in the interlaboratory test . Error! Bookmark not defined.
A.5 Results . Error! Bookmark not defined.
B.1 General . Error! Bookmark not defined.
B.2 Certified reference material (CRM) . Error! Bookmark not defined.
B.3 Reference material (RM) . Error! Bookmark not defined.
Bibliography . Error! Bookmark not defined.
Foreword . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Significance and use . 4
6 Apparatus . 5
7 Sampling . 6
7.1 Shape and dimension of specimen . 6
7.2 Pre-treatment . 6
7.3 Storage . 6
7.4 Number of specimens . 6
8 Procedure . 6
8.1 Dimension measurement of specimen . 6
8.2 Placement of specimen . 7
8.3 Evacuating and purging the chamber . 7
8.4 Measurement of electrical conductivity . 7
8.5 Measurement of Seebeck coefficient . 7
9 Calculation . 8
9.1 Seebeck coefficient . 8
9.2 Electrical conductivity . 9
10 Expression of results . 10
10.1 Seebeck coefficient and electrical conductivity . 10
10.2 Variation of Seebeck coefficient as a function of temperature . 11
10.3 Variation of electrical conductivity as a function of temperature . 11
11 Test report . 12
Annex A (informative) Interlaboratory evaluation of Seebeck coefficient and electrical
conductivity of bulk-type thermoelectric materials . 14
iv © ISO 20222023 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 24687:20222023(E)
Annex B (informative) Periodic check of the apparatus (or equipment) by using a certified
reference material (CRM) or a reference material (RM) . 19
Bibliography . 20
© ISO 20222023 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO/FDIS 24687:20222023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patentswww.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL:
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at
www.iso.org/members.htmlwww.iso.org/members.html.
vi © ISO 20222023 – All rights reserved

---------------------- Page: 6 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 24687:20222023(E)

Fine ceramics (advanced ceramics, advanced technical
ceramics) — Measurement of Seebeck coefficient and electrical
conductivity of bulk-type thermoelectric materials at room and
high temperatures
1 Scope
This document specifies the measurement methods for the electronic transport properties of bulk-type
thermoelectric materials at room and elevated temperatures. The measurement methods cover the
simultaneous determination of Seebeck coefficient and electrical conductivity of bulk-type
thermoelectric materials in a temperature range from 300 K to 1 200 K. The measurement methods are
applicable to bulk-type thermoelectric materials used for power generation, energy harvesting, cooling
and heating, among other things.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 23331, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for total
Formatted: Pattern: Clear
electrical conductivity of conductive fine ceramics
Formatted: Pattern: Clear
Formatted: Pattern: Clear
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
3.1
thermoelectric figure of merit
zT
dimensionless factor representing the thermoelectric conversion efficiency of a given material
3.2
thermoelectric power factor
2
Sσ
characteristic value of a thermoelectric material given by the product of the square of Seebeck coefficient
(S) and electrical conductivity (σ)
2
Note 1 to entry: The units of the thermoelectric power factor are watts per metre per square kelvin (W/mK ).
3.3
© ISO 20222023 – All rights reserved 1

---------------------- Page: 7 ----------------------
ISO/FDIS 24687:20222023(E)
Seebeck coefficient
S
intrinsic property which describes the induced voltage (thermal electromotive force, E) from a given
temperature difference (∆T) in a material
Note 1 to entry: The units of the Seebeck coefficient are microvolts per kelvin (μV/K).
3.4
electrical conductivity
σ
ability of a material to allow the transport of electric charges
Note 1 to entry: The units of electrical conductivity are Siemens per centimetre (S/cm).
4 Principle
This document is for simultaneously measuring the Seebeck coefficient and the electrical conductivity of
bulk-type thermoelectric materials using one measurement system. The off-axis four-terminal method
can be used to simultaneously measure the Seebeck coefficient and the electrical conductivity of bulk-
type thermoelectric material using one measurement system. As shown in Figure 1, the specimen is set
Formatted: Pattern: Clear
between two metal blocks in the heating zone and two thermocouple probes separately contact the
surface of the specimen. The measurement of the Seebeck coefficient of a bulk-type thermoelectric
material is necessary to measure the temperature difference between two positions (point H and point C)
on a specimen and the voltage across the two same positions (Figure 1). Seebeck coefficient can be Formatted: Pattern: Clear
calculated by following Formula (1).):
Formatted: Pattern: Clear
Formatted: Adjust space between Latin and Asian
S = E/∆T S E/∆T (1)
text, Adjust space between Asian text and numbers,
Tab stops: Not at 19.85 pt + 39.7 pt + 59.55 pt +
where
79.4 pt + 99.25 pt + 119.05 pt + 138.9 pt +
158.75 pt + 178.6 pt + 198.45 pt
 E is the induced thermoelectric voltage (thermal electromotive force) between the point H and
point C of the specimen;
Field Code Changed
 ∆T is the temperature difference between the point H and point C (= T - T ).
H C Formatted: Font: Not Italic
Formatted: Font: Not Italic
For Seebeck coefficient measurement, measured temperature is the average temperature of the hot- and
cold-side thermocouple probes.
Formatted: Font: Not Italic
By using the measuring system illustrated in Figure 2, electrical conductivity is also measured based on
Formatted: Pattern: Clear
the four-terminal method. This method is conducted by placing four probes. Constant current is applied
Formatted: Font: Italic
through the two outmost probes, causing a measurable voltage drop (, V), between the two inner probes.
Formatted: Pattern: Clear
The electrical resistance, R, is calculated using Ohm’s law (following Formula (2))):
Formatted: Adjust space between Latin and Asian
R = V/I R = V/ I (2)
text, Adjust space between Asian text and numbers,
Tab stops: Not at 19.85 pt + 39.7 pt + 59.55 pt +
79.4 pt + 99.25 pt + 119.05 pt + 138.9 pt +
where
158.75 pt + 178.6 pt + 198.45 pt
 V is the voltage;
Field Code Changed
 I is the current.
Formatted: Pattern: Clear
The resistivity, ρ, is be calculated by following Formula (3).):
Formatted: Adjust space between Latin and Asian
text, Adjust space between Asian text and numbers,
ρ = RA/l ρ = RA/ l (3)
Tab stops: Not at 19.85 pt + 39.7 pt + 59.55 pt +
79.4 pt + 99.25 pt + 119.05 pt + 138.9 pt +
where
158.75 pt + 178.6 pt + 198.45 pt
Field Code Changed
2 © ISO 20222023 – All rights reserved

=

---------------------- Page: 8 ----------------------
ISO/FDIS 24687:20222023(E)
 A is the cross-sectional area of the specimen;
 l is the separation between the two inner probes.
: R = V/I, where V is voltage and I is current as shown in Figure 2. The resistivity can be calculated as
follows: ρ = RA/l, where A is the cross-sectional area of the specimen, and l is the separation between the
two inner probes. The electrical conductivity is the reciprocal of the resistivity. For electrical conductivity
measurement, measured temperature is the actual temperature of the specimen, which generally can be
measured by furnace temperature.
24687_ed1fig1.EPS

Key
1 upper metal block 2 specimen
3 lower metal block 4 heater
5 point C 6 point H
7 upper thermocouple probe (cold side) 8 lower thermocouple probe (hot side)
9 current electrode 10 heating furnace
Figure 1 — Schematic diagram of off-axis four-terminal method for simultaneous measurement
of Seebeck coefficient and electrical conductivity
24687_ed1fig2.EPS
© ISO 20222023 – All rights reserved 3

---------------------- Page: 9 ----------------------
ISO/FDIS 24687:20222023(E)

Key
1 inner probes 2 outer probes
3 specimen 4 electrodes
Figure 2 — Schematic diagram of four-terminal method to measure the electrical resistivity
The results of an interlaboratory test are given in Annex A.
Formatted: Pattern: Clear
5 Significance and use
This document gives guidance for simultaneously measuring the high-accuracy and low-error Seebeck
coefficient and electrical conductivity of thermoelectric materials. Therefore, this standard is intended to
be used for the development, characterization and quality control of thermoelectric materials, data
acquisition for high-efficiency thermoelectric system design, etc.
Thermoelectric materials show Seebeck effect, Peltier effect and Thomson effect. The Seebeck effect is
the direct conversion of heat into electricity. The conversion efficiency of a thermoelectric material is
determined by the dimensionless thermoelectric figure of merit, zT, calculated following Formula (4):
2
Field Code Changed
zT = S σκT/ (4)
2
where (zT = SσT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal
conductivity and T is the absolute temperature).
 S is the Seebeck coefficient;
 σ is the electrical conductivity;
 κ is the thermal conductivity;
 T is the absolute temperature.
Thermoelectric materials show a trade-off relation between Seebeck coefficient and electrical
2
conductivity according to carrier concentration. Therefore, the accuracy of the power factor, Sσ, where
Formatted: Font: Not Italic
S is the Seebeck coefficient and σ is the electrical conductivity, can be improved through simultaneous
measurement of Seebeck coefficient and electrical conductivity in one run.
4 © ISO 20222023 – All rights reserved

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ISO/FDIS 24687:20222023(E)
6 Apparatus
6.1 6.1 Current source
The current source should be, accurate to ±0,5 % on ranges of -−1 A to +1 A used in the measurement.
Formatted: Font: Bold
Formatted: Font: Bold
6.2 6.2 Electronic voltmeter
Formatted: p2, Adjust space between Latin and Asian
-−7
text, Adjust space between Asian text and numbers
The electronic voltmeter should be, at least capable of measuring potential differences from 10 V to
-7
0,05 V with a resolution below 10 V.
Formatted: p2, Adjust space between Latin and Asian
text, Adjust space between Asian text and numbers
6.3 6.3 Conducting metal blocks.
Formatted: p2, Adjust space between Latin and Asian
text, Adjust space between Asian text and numbers,
The contact surface of conducting metal blocks shall be sufficiently large compared to a measurement
Tab stops: Not at 20 pt
specimen. A specimen shall be placed between two conducting metal blocks, such as platinum or
tungsten. One end of the specimen is heated while the other acts as a heat sink, dispersing heat, thus
cooling that side. In addition, the conducting metal blocks play a role as the electrodes for applying the
current when measuring the electrical conductivity.
NOTE Pt or Pt – Pd alloy is the best electrode material due to high measuring temperatures.
6.4 6.4 Thermocouple probes.
Formatted: p2, Adjust space between Latin and Asian
text, Adjust space between Asian text and numbers,
The diameter of thermocouple probes shall be 0,5 mm or less to obtain reproducible Seebeck coefficient Tab stops: Not at 20 pt
value. Thermocouples should have a resolution of at least 0,01 K or better. Thermocouple probes
integrating electrical probes for measuring the voltage and thermal probes for measuring the
temperature should be designed for working from 300 K to 1 200 K. Thermocouple probes should be
checked periodically as their output may drift with usage or contamination.
NOTE In some equipment, the voltage can be measured only with thermocouple wires without additional
electrical probes.
6.5 6.5 Test chamber.
Formatted: p2, Adjust space between Latin and Asian
text, Adjust space between Asian text and numbers,
The test chamber shall be capable of heating both the specimen and the conducting metal blocks up to at
Tab stops: Not at 20 pt
least 1 200 K as well as maintaining the test temperature within ±1 K during the test, by which vacuum
environment shall be available for test requirement. The test chamber should be evacuated below 3 Pa
and can be backfilled with a variety of gases such as helium, argon, nitrogen and oxygen or a mixture of
these. Low-pressure helium can be used to improve the thermal contact between the probe and the
sample. However, low pressure may affect the measured Seebeck coefficient. Determination of optimum
pressure of backfilled gas is required by Seebeck coefficient measurement according to gas pressure for
the same sample to be measured. For the measurement of oxides, oxygen partial pressure should be
controlled and monitored to avoid the reduction or oxidation of the samples.
6.6 6.6 Dimension-measuring device
, such as a Vernier-calliper or other devices used for measuring the dimensions of the specimen should
Formatted: p2, Adjust space between Latin and Asian
be, accurate to at least 0,01 mm in accordance with ISO 3611. text, Adjust space between Asian text and numbers
Formatted: Font: Bold
6.7 Periodic check of apparatus6.7 Apparatus and equipment
The apparatus (or equipment) should be, checked periodically through measuring a certified reference
Formatted: p2, Adjust space between Latin and Asian
material or a reference material to ensure if they are working properly (Refer tosee Annex B).
text, Adjust space between Asian text and numbers
© ISO 20222023 – All rights reserved 5

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ISO/FDIS 24687:20222023(E)
7 Sampling
7.1 Shape and dimension of specimen
The preferred shape of the specimen should be rectangular bar to ensure stable contacts with
thermocouple probes. The area of contact between the specimen and electrode is important, especially
to measure the Seebeck coefficient since this relates to heat transfer. The point of contact between the
specimen and the electrode is difficult to ensure the reliability of Seebeck coefficient measurement. The
two end sides of the specimen in contact with the metal blocks shall be parallel. The parallelism tolerance
of two end sides should be 0,01 mm or less. To secure the contact area between the specimen and the
electrode, surface roughness (, R ), of 10 μm or less is required. Figure 3 gives the recommended
a
Formatted: Pattern: Clear
dimensions of a rectangular bar-type specimen.
Dimensions in millimetres
24687_ed1fig3.EPS

Width Depth Length
b d L
1,5 to 5 1,5 to 5 5 to 25
Figure 3 — Recommended dimensions for a rectangular specimen
The cylindrical specimen can also be used. In this case, two thermocouple probes shall make stable
contacts on the surface of the specimen.
7.2 Pre-treatment
The surfaces of the specimen shall be ground and polished to ensure they are flat and acquire stable
contact with conducting metal blocks and thermocouple probes.
7.3 Storage
Specimens shall be stored separately and not allowed to impact or scratch each other.
7.4 Number of specimens
Three or more test pieces should be measured f
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24687
ISO/TC 206
Fine ceramics (advanced ceramics,
Secretariat: JISC
advanced technical ceramics) —
Voting begins on:
2023-01-26 Measurement of Seebeck coefficient
and electrical conductivity of bulk-
Voting terminates on:
2023-03-23
type thermoelectric materials at room
and high temperatures
Céramiques techniques — Mesurage du coefficient de Seebeck et de
la conductivité électrique de matériaux thermoélectriques de base à
températures ambiante et élevée
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 24687:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 1 ----------------------
ISO/FDIS 24687:2023(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24687
ISO/TC 206
Fine ceramics (advanced ceramics,
Secretariat: JISC
advanced technical ceramics) —
Voting begins on:
Measurement of Seebeck coefficient
and electrical conductivity of bulk-
Voting terminates on:
type thermoelectric materials at room
and high temperatures
Céramiques techniques — Mesurage du coefficient de Seebeck et de
la conductivité électrique de matériaux thermoélectriques de base à
températures ambiante et élevée
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: [phone]
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 24687:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 2 ----------------------
ISO/FDIS 24687:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Significance and use .4
6 Apparatus . 4
7 Sampling . 5
7.1 Shape and dimension of specimen . 5
7.2 Pre­treatment . 6
7.3 Storage . 6
7.4 Number of specimens . 6
8 Procedure .6
8.1 Dimension measurement of specimen . 6
8.2 Placement of specimen . 6
8.3 Evacuating and purging the chamber . 7
8.4 Measurement of electrical conductivity . 7
8.5 Measurement of Seebeck coefficient . 7
9 Calculation . 7
9.1 Seebeck coefficient. 7
9.2 Electrical conductivity . 9
10 Expression of results .10
10.1 Seebeck coefficient and electrical conductivity . 10
10.2 Variation of Seebeck coefficient as a function of temperature . 11
10.3 Variation of electrical conductivity as a function of temperature . 11
11 Test report .12
Annex A (informative) Interlaboratory evaluation of Seebeck coefficient and electrical
conductivity of bulk-type thermoelectric materials .14
Annex B (informative) Periodic check of the apparatus (or equipment) by using a certified
reference material (CRM) or a reference material (RM) .20
Bibliography .21
iii
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ISO/FDIS 24687:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 24687:2023(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Measurement of Seebeck coefficient and
electrical conductivity of bulk-type thermoelectric
materials at room and high temperatures
1 Scope
This document specifies the measurement methods for the electronic transport properties of bulk-
type thermoelectric materials at room and elevated temperatures. The measurement methods
cover the simultaneous determination of Seebeck coefficient and electrical conductivity of bulk-type
thermoelectric materials in a temperature range from 300 K to 1 200 K. The measurement methods are
applicable to bulk-type thermoelectric materials used for power generation, energy harvesting, cooling
and heating, among other things.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 23331, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for total
electrical conductivity of conductive fine ceramics
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
thermoelectric figure of merit
zT
dimensionless factor representing the thermoelectric conversion efficiency of a given material
3.2
thermoelectric power factor
2
S σ
characteristic value of a thermoelectric material given by the product of the square of Seebeck
coefficient (S) and electrical conductivity (σ)
2
Note 1 to entry: The units of the thermoelectric power factor are watts per metre per square kelvin (W/mK ).
1
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ISO/FDIS 24687:2023(E)
3.3
Seebeck coefficient
S
intrinsic property which describes the induced voltage (thermal electromotive force, E) from a given
temperature difference (∆T) in a material
Note 1 to entry: The units of the Seebeck coefficient are microvolts per kelvin (μV/K).
3.4
electrical conductivity
σ
ability of a material to allow the transport of electric charges
Note 1 to entry: The units of electrical conductivity are Siemens per centimetre (S/cm).
4 Principle
This document is for simultaneously measuring the Seebeck coefficient and the electrical conductivity of
bulk-type thermoelectric materials using one measurement system. The off-axis four-terminal method
can be used to simultaneously measure the Seebeck coefficient and the electrical conductivity of bulk-
type thermoelectric material using one measurement system. As shown in Figure 1, the specimen is
set between two metal blocks in the heating zone and two thermocouple probes separately contact
the surface of the specimen. The measurement of the Seebeck coefficient of a bulk-type thermoelectric
material is necessary to measure the temperature difference between two positions (point H and
point C) on a specimen and the voltage across the two same positions (Figure 1). Seebeck coefficient
can be calculated by following Formula (1):
SE= /ΔT (1)
where
E is the induced thermoelectric voltage (thermal electromotive force) between the point H and
point C of the specimen;
∆T is the temperature difference between the point H and point C (= T ­ T ).
H C
For Seebeck coefficient measurement, measured temperature is the average temperature of the hot-
and cold­side thermocouple probes.
By using the measuring system illustrated in Figure 2, electrical conductivity is also measured based
on the four-terminal method. This method is conducted by placing four probes. Constant current is
applied through the two outmost probes, causing a measurable voltage drop, V, between the two inner
probes. The electrical resistance, R, is calculated using Ohm’s law following Formula (2):
RV= /I (2)
where
V is the voltage;
I is the current.
The resistivity, ρ, is be calculated following Formula (3):
ρ=RA /l (3)
2
  © ISO 2023 – All rights reserved

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ISO/FDIS 24687:2023(E)
where
A is the cross­sectional area of the specimen;
l is the separation between the two inner probes.
The electrical conductivity is the reciprocal of the resistivity. For electrical conductivity measurement,
measured temperature is the actual temperature of the specimen, which generally can be measured by
furnace temperature.
Key
1 upper metal block 2 specimen
3 lower metal block 4 heater
5 point C 6 point H
7 upper thermocouple probe (cold side) 8 lower thermocouple probe (hot side)
9 current electrode 10 heating furnace
Figure 1 — Schematic diagram of off-axis four-terminal method for simultaneous measurement
of Seebeck coefficient and electrical conductivity
3
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ISO/FDIS 24687:2023(E)
Key
1 inner probes 2 outer probes
3 specimen 4 electrodes
Figure 2 — Schematic diagram of four-terminal method to measure the electrical resistivity
The results of an interlaboratory test are given in Annex A.
5 Significance and use
This document gives guidance for simultaneously measuring the high-accuracy and low-error Seebeck
coefficient and electrical conductivity of thermoelectric materials. Therefore, this standard is intended
to be used for the development, characterization and quality control of thermoelectric materials, data
acquisition for high-efficiency thermoelectric system design, etc.
Thermoelectric materials show Seebeck effect, Peltier effect and Thomson effect. The Seebeck effect is
the direct conversion of heat into electricity. The conversion efficiency of a thermoelectric material is
determined by the dimensionless thermoelectric figure of merit, zT, calculated following Formula (4):
2
zT =STσκ/ (4)
where
S is the Seebeck coefficient;
σ is the electrical conductivity;
κ is the thermal conductivity;
T is the absolute temperature.
Thermoelectric materials show a trade-off relation between Seebeck coefficient and electrical
2
conductivity according to carrier concentration. Therefore, the accuracy of the power factor, S σ, where
S is the Seebeck coefficient and σ is the electrical conductivity, can be improved through simultaneous
measurement of Seebeck coefficient and electrical conductivity in one run.
6 Apparatus
6.1 Current source, accurate to ±0,5 % on ranges of −1 A to +1 A used in the measurement.
4
  © ISO 2023 – All rights reserved

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ISO/FDIS 24687:2023(E)
−7
6.2 Electronic voltmeter, at least capable of measuring potential differences from 10 V to 0,05 V
­7
with a resolution below 10 V.
6.3 Conducting metal blocks.
The contact surface of conducting metal blocks shall be sufficiently large compared to a measurement
specimen. A specimen shall be placed between two conducting metal blocks, such as platinum or
tungsten. One end of the specimen is heated while the other acts as a heat sink, dispersing heat, thus
cooling that side. In addition, the conducting metal blocks play a role as the electrodes for applying the
current when measuring the electrical conductivity.
NOTE Pt or Pt – Pd alloy is the best electrode material due to high measuring temperatures.
6.4 Thermocouple probes.
The diameter of thermocouple probes shall be 0,5 mm or less to obtain reproducible Seebeck
coefficient value. Thermocouples should have a resolution of at least 0,01 K or better. Thermocouple
probes integrating electrical probes for measuring the voltage and thermal probes for measuring the
temperature should be designed for working from 300 K to 1 200 K. Thermocouple probes should
...