Promising room temperature thermoelectric conversion efficiency of zinc-blende AgI from first principles.

The theoretical investigation on structural, vibrational, electronic properties of zinc-blende(ZB) AgI were carried out employing first principles density functional theory calculations. Thermoelectric properties then were predicted through semi-classical Boltzmann transport equations within the constant relaxation time approximation. Equilibrium lattice parameter, bulk modulus, elastic constants and vibrational properties were calculated by using Generalized Gradient Approximation (GGA). Calculated properties are in good agreement with available experimental values. Electronic and thermoelectric properties were investigated both with and without considering spin-orbit coupling (SOC) effect which is found to have a strong influence on $p$-type Seebeck coefficient as well as the power factor of the ZB-AgI. By inclusion of SOC, a reduction of the band-gap and $p$-type Seebeck coefficients as well as the power factor was found which is the indication of that spin-orbit interaction cannot be ignored for $p$-type thermoelectric properties of the ZB-AgI. By using deformation potential theory for electronic relaxation time and experimentally predicted lattice thermal conductivity, we obtained a $ZT$ value 1.69 (0.89) at 400 K for $n$-type($p$-type) carrier concentration of 1.5$\times$10$^{18}$ (4.6$\times$10$^{19}$) cm$^{-3}$ that makes ZB-AgI as a promising room temperature thermoelectric material.