Small polaron transport and pressure dependence of the electrical resistivity of La2-xSrxNiO4 (0≤x≤1.2) -: art. no. 125116

Measurements of the electrical resistivity rho as a function of temperature T and pressure P(Pless than or equal to1.6 GPa) are reported on La2-xSrxNiO4 (0less than or equal toxless than or equal to1.2). A compositionally induced M-I transition occurs for xgreater than or equal to0.9. The data suggest small dielectric polaron conduction, with thermal-activated behavior at high temperatures and with three-dimensional variable range hopping at low temperatures for all compositions. Pressure is shown to weakly affect rho, for example, near room temperature a rate of -8.2%/GPa (drho/dP = -0.57 mOmega/GPa) is observed for x = 0.8. Fits to the data for the same composition in the temperature range 100 Kless than or equal toTless than or equal to300 K provide a thermally activated polaron hopping energy E-A = 30.3 meV and dE(A)/dP = -2.80 (meV/GPa). No superconductivity was observed at pressures up to 1.6 GPa and temperatures down to 4.2 K for any of the studied compositions. Our measurements provide strong evidence for polaron-dominated electrical conduction in these charge transfer gap materials.