Carrier concentration mediated enhancement in thermoelectric performance of various polymorphs of hafnium oxide: a plausible material for high temperature thermoelectric energy harvesting application

Autor: Rajesh Kumar, Ramesh Kumar, Mukhtiyar Singh, Deshraj Meena, Ankush Vij
Rok vydání: 2022
Předmět:
Zdroj: Journal of Physics D: Applied Physics. 55:495302
ISSN: 1361-6463
0022-3727
DOI: 10.1088/1361-6463/ac9986
Popis: The optimization of figure of merit by tuning carrier concentrations is an effective way to realize efficient thermoelectrics (TEs). Recently, the feasibility of high p-type carrier concentration (order of ∼1022cm−3) is experimentally demonstrated in various polymorphs of hafnium oxide (HfO2). In light of these studies, using the first-principles calculation combined with the semi-classical Boltzmann transport theory and phonon dynamics, we realized high TE performance in various polymorphs of HfO2 in a range of carrier concentrations at high temperatures. The phonon dispersion calculations confirm the dynamical stability of all polymorphs. The observed values of the Seebeck coefficient are 945.27 mV K−1, 922.62 mV K−1, 867.44 mV K−1, and 830.81 mV K−1 for tetragonal (t), orthorhombic (o), monoclinic (m), and cubic (c) phases of HfO2, respectively, at 300 K. These values remain positive at all studied temperatures which ensures the p-type behaviour of HfO2 polymorphs. The highest value of electrical conductivity (2.34 × 1020 Ω−1m−1s−1) observed in c-HfO2 at 1200 K, and the lowest value of electronic thermal conductivity (0.37 × 1015 W mK s−1) observed in o-HfO2 at 300 K. The lattice thermal conductivities at room temperature are 5.56 W mK−1, 2.87 W mK−1, 4.32 W mK−1, and 1.75 W mK−1 for c-, m-, o- and t- HfO2, respectively which decrease to 1.58 W mK−1, 0.92 W mK−1, 1.12 W mK−1, 0.53 W mK−1 at 1200 K for respective phases. The low lattice thermal conductivities lead to the high values of the figure of merit, i.e. 0.97, 0.87, 0.83, and 0.77 at 1200 K for the m-, o-, t-, and c- HfO2, respectively, at the optimized carrier concentrations (∼1021 cm−3). The predicted optimized carrier concentrations for various phases are in close agreement with the experimental reports. The estimated high figure of merit can make HfO2 a potential material for TE energy harvesting applications at elevated temperatures.
Databáze: OpenAIRE
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