The influence of hydrostatic pressure on the electrical conductivity and optical properties of chain-layered TlInSe2 and TlInSe2-TlInS2 solid solutions

The influence of hydrostatic pressure on the electrical conductivity of TlInSe2 and on the optical transmission spectra of TlInSe1.4S0.6 crystals grown by the Bridgman method are reported for the first time. The measurements were performed at room temperature at hydrostatic pressures P up to 1.4 GPa (conductivity measurements) and 1 GPa (optical transmission measurements). The increase of conductivity with pressure is described by the formula sigma(P) = sigma(O) exp(-GP/2kT), where G = dE(g)(i)/dP = 1.75 x 10(-1) eV/GPa is the pressure coefficient of the indirect band gap. It is shown that dE(g)(i)/dP changes abruptly at x approximate to 0.3 (composition at which the structural transformation from the tetragonal TlInSe2 to the monoclinic TlInS2 takes place) for the solid solutions TlInSe2xS2(1-x). An abrupt change of dE(g)(i)/dP observed for TlInSe1.4S0.6 at P approximate to 0.72 GPa is assigned as due to a structural phase transformation under pressure. It is found that with increasing amount of Se in the TlInSe2-TlInS2 system the value of pressure at which the phase transition takes place shifts to higher pressures (P approximate to 0.66 GPa for TlInS2, P approximate to 0.72 GPa for TlInSe1.4S0.6).