APS March Meeting 2024
Monday–Friday, March 4–8, 2024;
Minneapolis & Virtual
Session N64: Advances in Thermal Energy Conversion
11:30 AM–2:18 PM,
Wednesday, March 6, 2024
Room: 211AB
Sponsoring
Unit:
GERA
Chair: Waldemar Kaiser, TU Munich
Abstract: N64.00006 : Enhancing Thermoelectric Properties of Some Defect Pyrochlores by Lowering Thermal Conductivity
12:30 PM–12:42 PM
Abstract
Presenter:
Sepideh Akhbarifar
(The Catholic University of America)
Author:
Sepideh Akhbarifar
(The Catholic University of America)
Collaboration:
Dr. Werner Lutze, Dr. Nicholas A. Mecholsky, Dr. Ian L. Pegg
Lowering thermal conductivity (κ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>κ) is vital in designing thermoelectrics as it can significantly increase their figure of merit. This study aims to lower κ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>κ by changing site occupancies in metal-like defect pyrochlores (A2B2O6O´x, 0≤x<1), specifically Pb2Ru2O6O´0.5, and derivatives with electron lone pairs on the A site and vacancies on the O´ site. Partial B site substitutions (Pb2+2(Ru4+2-yPb4+y)O6.5-x, y = 0, 0.3, 0.5, 0.7, 0.9) increased the lattice parameter (VIPb4+ > VIRu4+), affected electrical conductivity (σ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>σ) and replaced Pb–O–Ru by Pb–O–Pb bonds. The number of lone pair electrons (VIIIPb2+ on A site) remained constant. Removing some Pb2+ from the A site (Pb1.8Ru2O6O´x, 0.5≤x<1) reduces lone pair electrons and introduces O´ vacancies. ‘x’ indicates potential changes in the number of O´ vacancies (not measured). In all cases, lattice defects and resulting anharmonicity increase phonon scattering κ<!--[if gte msEquation 12]>κ and σ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>σ were measured and the underlying scattering processes were explained by existing quantum-physical models. Relative to Pb2Ru2O6.5, derivatives showed up to 2.3× increase of σ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>σ and significant decreases in κL, the lattice component of κ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>κ, (κ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>κ = κe + κL). Lowering Pb2+ on the A site yielded the electronic component κe to be greater than σ<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>σ and the lattice component κL to be negative, suggesting failure of the Wiedemann-Franz law when using the Sommerfeld value for the Lorenz number (L) to calculate κe. This phenomenon will be discussed along with an attempt to calculate a correct L using Seebeck coefficient.