Title: Heat capacity of Mg3Sb2, Mg3Bi2, and their alloys at high temperature

Journal Article · · Materials Today Physics
ORCiD logo [1];  [1];  [1]; ORCiD logo [2];  [2];  [3];  [4];  [4];  [5];  [1]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Jet Propulsion Lab./California Inst. of Technology (CalTech), Pasadena, CA (United States)
  3. Michigan State Univ., East Lansing, MI (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States)
  5. Argonne National Lab. (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)
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The thermoelectric figure of merit reported for n-type Mg3(Sb,Bi)2 compounds has made these materials of great engineering significance, increasing the need for accurate evaluations of their thermal conductivity. Thermal conductivity is typically derived from measurements of thermal diffusivity and determination of the specific heat capacity. The uncertainty in this method (often 10% or more) is frequently attributed to measurement of heat capacity such that estimated values are often more accurate. Inconsistencies between reported thermal conductivity of Mg3(Sb,Bi)2 compounds may be attributed to the different values of heat capacity measured or used to calculate thermal conductivity. The high anharmonicity of these materials can lead to significant deviations at high temperatures from the Dulong-Petit heat capacity, which is often a reasonable substitute for measurements at high temperatures. Herein, a physics-based model is used to assess the magnitude of the heat capacity over the entire temperature range up to 800 K. The model agrees in magnitude with experimental low-temperature values and reproduces the linear slope observed in high-temperature data. Owing to the large scatter in experimental values of high-temperature heat capacity, the model is likely more accurate (within ±3%) than a measurement of a new sample even for doped or alloyed materials. It is found that heat capacity for the solid solution series can be simply described (for temperatures: 200K≤T≤800K ) by the polynomial equation: cp[Jg–1K–1]=3NR/MW(1 + 1.3 × 10–4 T – 4 × 103 T–2), where 3NR = 124.71 J mol–1K–1, MW is the molecular weight [gmol–1] of the formula unit being considered, and T is temperature in K. This heat capacity is recommended to be a standard value for reporting and comparing the thermal conductivity of Mg3(Sb,Bi)2 including doped or alloyed derivatives. Furthermore, a general form of the equation is given which can be used for other material systems

Research Organization:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1489260
Journal Information:
Materials Today Physics, Journal Name: Materials Today Physics Journal Issue: C Vol. 6; ISSN 2542-5293
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (8)

Improvement of Low‐Temperature zT in a Mg 3 Sb 2 –Mg 3 Bi 2 Solid Solution via Mg‐Vapor Annealing journal July 2019
Phase Transformation Contributions to Heat Capacity and Impact on Thermal Diffusivity, Thermal Conductivity, and Thermoelectric Performance journal July 2019
Extraordinary n‐Type Mg 3 SbBi Thermoelectrics Enabled by Yttrium Doping journal June 2019
Enhanced Thermoelectric Performance in N‐Type Mg 3.2 Sb 1.5 Bi 0.5 by La or Ce Doping into Mg journal January 2020
Exceptional thermoelectric performance in Mg 3 Sb 0.6 Bi 1.4 for low-grade waste heat recovery journal January 2019
Improved stability and high thermoelectric performance through cation site doping in n-type La-doped Mg 3 Sb 1.5 Bi 0.5 journal January 2018
The manipulation of substitutional defects for realizing high thermoelectric performance in Mg 3 Sb 2 -based Zintl compounds journal January 2019
The importance of the Mg–Mg interaction in Mg 3 Sb 2 –Mg 3 Bi 2 shown through cation site alloying journal January 2020

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36 MATERIALS SCIENCE
Heat capacity
Mg3Bi2
Mg3Sb2
Thermal conductivity
Thermoelectric