Abstract
The optimization of thermoelectric materials for use in various applications, such as spacecraft power generation, waste heat recovery, and Peltier coolers, requires a careful optimization of material properties. This can be achieved via defect engineering in which defects are purposefully added to a material to produce desired properties. In this tutorial, we discuss a defect engineering strategy called phase-boundary mapping. While many compound thermoelectric semiconductors are often called “line compounds” due to their appearance as a line on a binary phase diagram, in reality, due to the laws of thermodynamics, all phases have a finite phase width. The edges of this phase space define the chemical potential of the material. By making small compositional changes across this phase space, appreciable differences in thermoelectric properties are observed due to this change in the chemical potential. Additionally, the phase equilibria of a thermoelectric material impacts alloying and dopability that further impacts material properties. Phase-boundary mapping is a strategy that allows us to explore the limits of a material and ultimately reproducibly optimize thermoelectric performance by considering the effects of off-stoichiometry on chemical potential, and thus defect energies and material properties. This technique can be applied in the optimization of numerous thermoelectric materials as well as extended to other semiconductors with properties controlled by defects.
- Received 7 June 2022
- Revised 12 August 2022
DOI:https://doi.org/10.1103/PRXEnergy.1.022001
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Thermoelectric materials are an important tool for achieving our goal of a more energy efficient and sustainable world. By converting a temperature gradient to electricity and vice versa, thermoelectrics have been used in a variety of applications including as remote power sources in NASA space vehicles and as coolers for more environmentally friendly refrigeration applications. However, the improvement of thermoelectric efficiency relies on optimization of often opposing material properties that tend to depend on defects present in the material. Here, the authors discuss a framework for studying and optimizing thermoelectric materials known as phase boundary mapping, which uses a phase-diagram-based approach to explore and control structural defects. This method has been used in more than a dozen studies on thermoelectric materials, an overview of which is provided here. In this Tutorial, the underlying physics and thermodynamics of phase boundary mapping are discussed, and practical steps towards designing future phase-boundary-mapping studies for thermoelectric materials and beyond are outlined.
