Comparative analysis of electronic and thermoelectric properties of strained and unstrained IrX3 (X = P, As) skutterudite materials

The electronic and thermoelectric properties of unfilled IrP3 and IrAs3 skutterudite materials under hydrostatic pressures are investigated using density functional theory (DFT) combined with semi-classical Boltzmann transport theory. Calculations of the elastic properties and phonon frequencies for both strained and unstrained materials demonstrate that they are mechanically and dynamically stable, with ductility varying depending on the applied pressure. For pressures ranging from 0 to 30 GPa, band structure calculations using the GGA+TB-mBJ approximation reveal that the band gap varies from 0.400 to 0.144 eV for IrP3 and from 0.341 to 0.515 eV for IrAs3. At 0 GPa, IrAs3 exhibits a direct band gap, whereas IrP3 has an indirect band gap. As pressure increases, IrAs3 undergoes a transition from a direct to an indirect band gap above 10 GPa, whereas IrP3 maintains its indirect band gap throughout the pressure range. Thermoelectric properties, including the Seebeck coefficient, electrical conductivity, thermal conductivity (both electronic and lattice contributions), and relaxation time, are also computed across various pressures and temperatures ranging from 300 to 1200 K. The ideal conditions for efficient thermoelectric performence in IrAs3 are achieved at 30 GPa and 1200 K, with an optimal n-type doping concentration of 56 x 10(19 )cm(-3), resulting in a ZT of 0.68. For IrP3, a ZT of approximately 0.46 is obtained at 600 K and 5 GPa, with a p-type doping concentration of 6.0 x 10(18 )cm(-3). The present study provides valuable insights into the behavior of skutterudite materials under strain, offering potential pathways for enhancing their performance in practical applications.