Ultralow lattice thermal conductivity of chalcogenide perovskite CaZrSe3 contributes to high thermoelectric figure of merit

Abstract

An emerging chalcogenide perovskite, CaZrSe 3 , holds promise for energy conversion applications given its notable optical and electrical properties. However, knowledge of its thermal properties is extremely important, e.g. for potential thermoelectric applications, and has not been previously reported in detail. In this work, we examine and explain the lattice thermal transport mechanisms in CaZrSe 3 using density functional theory and Boltzmann transport calculations. We find the mean relaxation time to be extremely short corroborating an enhanced phonon-phonon scattering that annihilates phonon modes, and lowers thermal conductivity. In addition, strong anharmonicity in the perovskite crystal represented by the Grüneisen parameter predictions, and low phonon number density for the acoustic modes, results in the lattice thermal conductivity to be limited to 1.17 W m −1 K −1. The average phonon mean free path in the bulk CaZrSe 3 sample (N → ∞) is 138.1 nm and nanostructuring CaZrSe 3 sample to~10 nm diminishes the thermal conductivity to 0.23 W m −1 K −1. We also find that p-type doping yields higher predictions of thermoelectric figure of merit than n-type doping, and values of ZT~0.95-1 are found for hole concentrations in the range 10 16-10 17 cm −3 and temperature between 600 and 700 K.

Phonon anharmonicity in binary chalcogenides for efficient energy harvesting

“…A larger phonon gap limits the number of decay channels for optical phonons (for example, pristine GeTe exhibits a phonon gap ∼10 meV, in contrast to ∼4 meV in SnSe) 71,152,174,175 necessitating a four-phonon decay. Three-phonon decay processes have also been observed with Raman spectroscopy in other chalcogenide-based TE materials such as PdS, 178 CaZrSe 3 , 179 PbSe, and SnTe. 180 On the other hand, four-phonon processes could dominate phonon decay in materials that exhibit anomalous anharmonicity, where phonon modes soften instead of hardening with decreasing temperature.…”

Colloidal BaZrS3 chalcogenide perovskite nanocrystals for thin film device fabrication

“…The thermal expansion coefficient serves as a design parameter for materials having low thermal lattice conductivity, and hence has application in designing thermoelectric materials 47. This low thermal volume expansion of BaZrS 3 NCs gives an indication that they could have low thermal conductivity which has been recently reported 48,49. To study the local structure of BaZrS 3 NCs, we have recorded the temperature-dependent X-ray absorption fine structure (XAFS) data of the samples at the Zr K-edge in the transmission mode at the Scanning EXAFS beamline (BL-09) at the Indus-2 synchrotron source (2.5 GeV, 200 mA) at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, India.…”

“…47 This low thermal volume expansion of BaZrS 3 NCs gives an indication that they could have low thermal conductivity which has been recently reported. 48,49 To study the local structure of BaZrS 3 NCs, we have recorded the temperature-dependent X-ray absorption fine structure (XAFS) data of the samples at the Zr K-edge in the transmission mode at the Scanning EXAFS beamline (BL-09) at the Indus-2 synchrotron source (2.5 GeV, 200 mA) at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, India. The details of the experimental methodology and data analysis are given in the ESI.…”

Anisotropic Chalcogenide Perovskite CaZrS3: A Promising Thermoelectric Material

“…The excellent TE materials characterized with ZT ≥ 1 should possess a large Seebeck coefficient and a high electrical conductivity but a low thermal conductivity concurrently. 29 Nevertheless, due to the strong coupling of these coefficients, for example, the electronic thermal conductivity (κ e ) is proportional to the electrical conductivity as given by the Wiedemann−Franz law (κ e = LσT, where L is the Lorentz number), it is a huge challenge to enhance the power factor (PF = S 2 σ) and reduce the thermal conductivity simultaneously. 30 Focusing on these issues, some strategies such as nanostructures, carrier concentration engineering, and band structure engineering have been employed to improve the conversion efficiency of the existing traditional and commercial TE materials.…”

“…17 Recently, the potential TE applications of chalcogenide perovskites have been reported by theoretical researchers, 19,35,36 for example, in anisotropic CaZrSe 3 with strong lattice anharmonicity, a high Debye temperature and a short phonon lifetime contribute to an ultralow κ l and competitive ZT predictions for potential TE applications. 29,37 In addition, it was found that orthorhombic BaZrS 3 displays a strong directional dependence and achieves a considerable ZT e (considering only the electronic thermal conductivity κ e ) of 1.08 based on the high Seebeck coefficient (3000 μV K −1 ). 38 On the other hand, due to the strong anharmonicity, short phonon lifetime, and low phonon number density, BaZrS 3 yielded an ultralow κ l of 1.16 W m −1 K −1 at room temperature.…”