Computational study of half-metallic behavior, optoelectronic and thermoelectric properties of new XAlN3 (X = K, Rb, Cs) perovskite materials

In this study, we systematically explored the properties of novel perovskite materials, XAlN3 (X = K, Rb, and Cs), based on first-principles calculations and semiclassical Boltzmann transport theory. Generalized gradient approximation and HSE06 hybrid functional methods were used to investigate the electronic band structures. Our findings indicated intriguing half-metallic behavior where the spin-down state had metallic characteristics, whereas the spin-up state behaved as an insulator for all compounds, with indirect band gaps. These compounds had a significant magnetic moment of 5 mu(B), which confirmed their half-metallic nature. Analysis of the elastic constants indicated distinctive mechanical properties. Moreover, the dielectric functions indicated efficient energy absorption across a broad energy spectrum, which is particularly beneficial for ultraviolet optoelectronic applications. At 300 K with a chemical potential (mu) of +1.37 eV, CsAlN3 had a notable thermoelectric figure of merit (ZT) of 0.99. This ZT value remained competitive at 0.97, even at a high temperature of 1000 K in the p-type region. However, the ZT and Seebeck coefficients decreased in a temperature-dependent manner to affect the thermoelectric characteristics of these materials. Overall, our findings suggest that XAlN3 (X = K, Rb, and Cs) perovskite materials are promising candidates for use in various applications in spintronics, optoelectronics, and thermoelectric devices.