The use of strain to tailor electronic thermoelectric transport properties: A first principles study of 2H-phase CuAlO₂

Abstract

Using first principles calculations, the use of strain to adjust electronic transport and the resultant thermoelectric (TE) properties is discussed using 2H phase CuAlO2 as a test case. Transparent oxide materials, such as CuAlO2, a p--type transparent conducting oxide (TCO), have recently been studied for high temperature thermoelectric power generators and coolers for waste heat. Given TCO materials with relative ease of fabrication, low cost of materials, and non-toxicity, the ability to tailor them to specific temperature ranges, power needs, and size requirements, through the use of strain opens an interesting avenue. We find that strain can have a significant effect on these properties, in some cases detrimental and in others beneficial, including the potential for n--type power factors larger than the highest p--type case. The physical reasons for this behavior are explained in the terms of the thermoelectric transport distribution and the Landauer distribution of modes. I. IntroductionThermoelectric (TE) devices and materials hold great promise for broad use in solid--state energy generation and solid--state cooling. However, as robust and reliable as these devices are, they have been limited by low conversion efficiencies since their inception 1-5 . The past three decades have witnessed the thermoelectric material figure of merit, zT, improved from under one to over two 5 . These gains have been primarily driven by a reduction in the lattice thermal conductivity of materials and devices through the use of nano--structuring 6-12 and the development of novel materials that have an inherently low thermal conductivity due to large discrepancies in the masses of their constituent elements. These advances, however, have not translated into working devices 13 . As we approach the lower limit of the lattice thermal conductivity for common and even complex TE materials at room temperature and above, the variety of avenues capable of moving the field of thermoelectrics forward are being narrowed, therefore ideas that have the potential to advance the field need to be explored carefully. In this paper we look at an alternate route forward, given materials with relative ease of fabrication, low cost, and non--toxicity, the ability to tailor them to specific

The use of strain and grain boundaries to tailor phonon transport properties: A first-principles study of 2H-phase CuAlO2. II

“…In part I of this study [19], it was found that +1% strain in the z direction induced the highest power factors for both n and p type transport in 2H--CuAlO2. A structure with +1% strain in the z direction was simulated for both a crystalline (no grains) as well as for a structure with 3nm grains.…”

“…As we approach the lower limit of the lattice thermal conductivity for complex TE materials the applicability of the field of thermoelectrics remains in question due to the cost and efficiency of working devices. A previous work [19] looked at transparent conducting oxides (TCOs), and specifically 2H--phase CuAlO2, which has gained interest as a promising candidate for high temperature p--type thermoelectric applications [20]- [23] [24], because of its potential use in high temperature applications, due to a large band gap, high thermal stability, oxidation resistance, and low material costs [20], [21], [25]- [34]. Some experimental and theoretical studies [19], [20], [24], [35]- [37], have been done on the thermoelectric (TE) properties of the 2H phase of this material, however none have looked at the thermal conductivity using rigorous first principles simulations.…”

“…A previous work [19] looked at transparent conducting oxides (TCOs), and specifically 2H--phase CuAlO2, which has gained interest as a promising candidate for high temperature p--type thermoelectric applications [20]- [23] [24], because of its potential use in high temperature applications, due to a large band gap, high thermal stability, oxidation resistance, and low material costs [20], [21], [25]- [34]. Some experimental and theoretical studies [19], [20], [24], [35]- [37], have been done on the thermoelectric (TE) properties of the 2H phase of this material, however none have looked at the thermal conductivity using rigorous first principles simulations. Under specific cases of strain, n--type conduction can produce higher power factors than their p--type counterparts providing an interesting avenue for strain engineering to produce both n and p type legs from the same material [19].…”

“…Some experimental and theoretical studies [19], [20], [24], [35]- [37], have been done on the thermoelectric (TE) properties of the 2H phase of this material, however none have looked at the thermal conductivity using rigorous first principles simulations. Under specific cases of strain, n--type conduction can produce higher power factors than their p--type counterparts providing an interesting avenue for strain engineering to produce both n and p type legs from the same material [19]. Strain may be beneficial for the electronic component of zT, but its effect on the lattice thermal conductivity must also be ascertained.…”

Machine Learning Regression Guided Thermoelectric Materials Discovery – A Review

“…[3][4][5] TE properties are complex transport properties, which are hard to be determined both from experimental measurement and theoretical calculation. [6][7][8] To address the current bottleneck of the TE technology, uncover new TE materials with desired performance is urgently needed. Thanks to the everlasting contribution from the TE community, tremendous in-depth research with fruitful research data makes the data-driven approach achievable.…”