Comparative study of cubic and tetragonal NaCaF3 perovskites: Structural, mechanical, electronic, and thermoelectric properties

This study aims to systematically investigate and compare the structural, mechanical, vibrational, electronic, and thermoelectric properties of cubic (c) and tetragonal (t) NaCaF 3 perovskite compounds using first-principles density functional theory (DFT) and Boltzmann transport theory, with a focus on the effects of tetragonal distortion. In this work, we perform first-principles calculations interfaced with Boltzmann transport theory to study the carrier-dependent thermoelectric properties of NaCaF 3 -c and NaCaF 3 -t perovskite compounds. The calculated negative formation energy points to the structural stability of both NaCaF 3 -c and NaCaF 3 -t perovskite compounds. The phonon band structures indicate no negative frequency along any wave vector, demonstrating the dynamic stability of the studied compounds. The calculated elastic constants satisfy the Born criteria, ensuring mechanical stability. Due to their wide bandgap, we emphasize their potential applications in high-power and high-temperature environments and their suitability as host materials for substitutional doping. Using generalized gradient approximation (GGA) and Heyd–Scuseria–Ernzerhof (HSE) functional, the calculated indirect electronic bandgap is 4.99 eV and 6.78 eV for NaCaF 3 -c perovskite compound, respectively. Similarly, the GGA (HSE) calculated electronic bandgap is 4.86 eV (6.58 eV) for NaCaF 3 -t, perovskite compound. The materials exhibit insulating behavior with an indirect bandgap, rendering them promising candidates for electronic devices. NaCaF 3 -c and NaCaF 3 -t have wide bandgap and are suitable candidate materials for defects to tune the structural and electronic properties required for various device desired applications. The low lattice thermal conductivity are predicted for the studied compounds among which the NaCaF 3 -t has the minimum value of κ l a t 2 W m −1 K −1 @ 500 K. Furthermore, our electron (hole) doping examination reveals favorable thermoelectric performance, with figures-of-merit (ZT) approaching 1, indicating their efficiency for thermoelectric device applications.