Structure, stability, electronic and thermoelectric properties of strontium chalcogenides

The present investigation reports a critical insight on the temperature dependent transport properties of strontium chalcogenides (SrX; X = O, S, Se and Te) in their rock salt (rs-SrX) and hexagonal monolayer (h-SrX) phases, for the first time. For an initial check on the stability of these phases (rs-SrX and h-SrX), we have carried out phonon dispersion analysis under PAW-GGA level of calculations. Although, some of these structures are reported to be unstable under lower level (PAW-LDA) of calculations in past, our PAW-GGA computations reveals all the rs-SrX and h-SrX phases to be dynamically stable. The stability of all these structures along with wide band (indirect) gap certainly motivates us to look for their thermoelectric properties, for the first time. The electronic band structures and projected density of states (PDOS) of these materials are computed to understand their electronic properties. Finally, in order to obtain temperature dependent transport properties for the considered series, we have utilized the semi-classical Boltzmann transport equations (BTE). The Seebeck coefficient (S), electrical conductivity (sigma), thermal conductivity (kappa) and figure of merit (ZT) are calculated using BTE. Couple of monolayers (h-SrS and h-SrTe) and bulk (rock salt) phases (rs-SrO and rs-SrS) are come up with excellent thermoelectric properties through the present investigation.