Theoretical limits of thermoelectric figure of merit inn-typeTiO2polymorphs

Abstract

We calculate the conduction band structures and n-type thermoelectric transport properties for the TiO2 polymorphs rutile, anatase, and brookite from first principles within the constantrelaxation-time approximation. Although the Seebeck coefficient is nearly isotropic in all polymorphs, the power factor is anisotropic and takes its largest values along [100] in rutile and anatase, and along [010] for brookite. We also identify the free-carrier concentrations and temperatures that maximize the power factor. Our results for the theoretical upper bounds of the figure of merit at high temperature show that optimized rutile exhibits thermoelectric conversion efficiency that is superior to anatase and brookite and can reach values desirable for waste-heat recovery applications.

First-Principles Investigation of Structural, Thermal and Transport Properties of Anatase TiO2

“…It was found that rutile phase exhibits higher Seebeck coefficient compared to both anatase and brookite structures. 27 This result is consistent with that published by M. B. Ricoult. 28 For further analysis, as seen from Fig.…”

“…Compared to rutile structure, anatase phase exhibits higher electrical conductivity. 27 The thermal conductivity gives us an idea about the ability of a material to conduct heat caused by electrons and lattice vibrations. Thus, the total thermal conductivity (K = K el + K l ) consists of two parts: the electronic and lattice terms caused by electrons and lattice vibrations, respectively.…”

Perspective: n-type oxide thermoelectrics via visual search strategies

“…Bayerl and Kioupakis have reported theoretical investigation by a somewhat different approach of different TiO 2 polymorphs as potential n-type thermoelectrics and also find that rutile is exceptional. [49] The band structure of TiO 2 (bottom, right) has a double degenerate bottom conduction band at M , with a very flat CBM along the Γ-M directions. This underlies the favorable behavior.…”

Theoretical Evaluation of Thermal Properties of TiO2 Anatase and Rutile by using Einstein-Debye Approximation

“…Also, the some efficient solution approaches are also given in Refs. [12,13]. In spite of these progress, an alternative new approach is required for accurate evaluation of thermal properties of anatase and rutile TiO 2 .…”

“…The accurate evaluation problem of thermodynamic properties in various temperature ranges is extremely important for its application area to the conversion of heat into electric power [1,2]. In the studies dedicated to investigate the thermal properties of titanium dioxide, the various methods have been applied for the whole range of temperature [6][7][8][9][10][11][12][13][14]. Especially, in study [1], there are some significant numerical results of the isothermal bulk modules, heat capacities, entropy, thermal expansion coefficient and vibrational Helmholtz free energy for titanium dioxide.…”