Electrical transport properties of gadolinium scandium gallium garnet

Electrical conductivity and thermoelectric power are measured on a single crystal of Gd_3.0Sc_1.8Ga_3.2O₁₂ (GSGG) between 1273 and 1673 K. The measurements are made both in air and in controlled atmospheres, and P_O2 varies from 10^?1.68 to 10^?5.6 MPa. The data indicate GSGG may well be a mixed conductor in this temperature and P_O2 range, with n-type electronic conductivity and ionic transport on the oxygen sublattice. Changes in temperature induce long-lived disequilibrium in electrical conductivity of GSGG (over 30 h at T < 1373 K) that can be explained by temperature dependent cation redistribution. The effective activation energy for equilibrium electrical conductivity is E_a = 2.40 ± 0.05 eV, as opposed to values of E_a between 1.8 and 2.2 eV during actual temperature changes. An additional contribution in the equilibrium E_a, due to thermally activated cation redistribution, can account for the higher value seen.