Thermoelectric properties of TcX2(X=S, Se, Te)

We have studied the thermoelectric properties of TcX2 (X = S, Se, Te) by combined first-principles density functional theory with Boltzmann transport approach. The results show that TcS2 and TcSe2 have high Seebeck coefficients within a reasonable doping level, and their Seebeck coefficients are all at the magnitude of 10(-4) V/K, however, the Seebeck coefficients of TcTe2 are always smaller than 2 x 10(-4) V/K. The peak of Seebeck coefficient is uplifted as doping level decreases. The power factors have a promising value and can be greatly enhanced by p-type doping along all direction of TcS2, along x-direction of TcSe2, and along x- and y-direction of TcTe2, while by n-type doping for other directions. It finds that when the doping level is 1 x 10(19) cm(-3) the peak of power factor appears along z-direction of TcS2 and x-direction of TcSe2, and when the doping level reaches 1 x 10(29) cm(-3) the power factors along x- and y-direction of TcS2 and x-direction of TcSe2 reach its peak, meanwhile, the peaks of power factor along the x- and y-direction of TcTe2 occur when the doping level is 1 x 10(21) cm(-3). These results mean that we can optimize the Seebeck coefficients and power factor by proper doping, and TcX2 (X = S, Se, Te) is candidate for thermoelectric application. (C) 2018 Elsevier B.V. All rights reserved.