First principles comparative studies of thermoelectric and other properties in the cubic and hexagonal structure of CsCdCl3 halide perovskites

We present First-principles studies of cubic and hexagonal structured CsCdCl3, using Norm Conserving (PBE-NC) and Projected Augmented Wave (PBE-PAW) pseudopotentials. From our results, the hexagonal structure has direct bandgaps of 2.54 eV and 2.24 eV, within the PBE-PAW and PBE-NC pseudopotentials respectively. Whereas, the cubic structure possess bandgaps of 1.76 eV and 1.58 eV for PBE-PAW and PBE-NC pseudopotentials respectively. Also, from the elastic properties calculations, the results revealed higher values of Vicker's hardness, elastic constants C-11 and C-12, Young, Bulk and Shear moduli in the cubic structure than the hexagonal structure with the exemption in Pugh's ratio having a higher value in hexagonal structure. Further analysis of the calculated elastic properties reveals that CsCdCl3 is ductile and satisfied the conditions for elastic stability. Across calculated temperature range, the PBE-PAW pseudopotentials give higher electrical and thermal conductivity per relaxation time in the two structures, with a nearly linear increase in cubic and hexagonal structures. From 0 K up to the room temperature, the thermal conductivity per relaxation time in both pseudopotentials and crystal structures converged to the same values, while above 300 K the cubic phase has higher thermal conductivity per relaxation time. The hexagonal structure has a higher figure of merit with a significant peak located at 50 K with PBE-PAW and PBE-NC pseudopotential method. The work revealed that CsCdCl3 possess interesting thermoelectric properties and will be applicable as thermoelectric material. (C) 2019 Elsevier B.V. All rights reserved.