Probable thermoelectric materials for promising candidate of optoelectronics for Ba‐based complex perovskite compounds

Structural parameters, electronic band structure, optical spectra, and thermoelectric properties of trigonal Ba3B(Nb, Ta)2O9(B═Sr, Mg, Ca, Hg, Zn, Fe, Ni, Mn, Co, and Ca) compound materials are investigated. The computations are performed using density-functional calculations within the generalized gradient approximation. The calculated a and c parameters agree with those of the experiment to within 2%. The Ba3B(Nb, Ta)2O9(B=Sr,Mg,Ca, Hg, Zn, Fe, Ni, Mn, Co, and Ca) materials are found to be semiconductors with a band-gap energy varying from 0.82 to 3.17 eV. A metallic character is observed in Ba3B(Nb, Ta)2O9(B═Ni, Mn, and Co) compounds indicating the presence of conductivity features. A small carrier effective mass indicates the increase of the electron mobility leading to a high n-type conductivity. The p states dominate the lower valence band region. The optical spectra show an anisotropic character between x and z directions. The excitonic effects tend to increase the strength of the oscillator at M0 and M points. The effect is reduced when increasing the photon energy, indicating that the Ba3BB2'O9 compound can be used for devices such as Bragg's reflectors, and optical and optoelectronic devices. The calculations were performed using the BoltzTrap code, which depends on the semi-classical Boltzmann transport equation. The Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and the figure of merit for Ba3(Fe, Sr, Hg, Zn)B′2O9 are calculated. At higher temperatures, the mobility increases by reducing the electrical conductivity. Ba3(Fe, Sr, Hg, Zn) B2' O9 shows a considerable thermoelectric performance accompanied by a sign point figure of merit larger than many full perovskites reported till date.