Precipitation phenomena in and electrical resistivity of high-temperature treated langatate (La₃Ta_0.5Ga_5.5O₁₄)

摘要

La₃Ta_0.5Ga_{5.5,/sub>O14 (LTG) single crystals, which have no phase transition up to the melting point, were heat-treated in air at temperatures from 1000u000b0;C to 1450u000b0;C for 10 h. LaTaO4 (LT) and LaGaO3 (LG), which coexist with LTG in the three-phase region on the Ga-poor side, precipitated on the surface of the crystal for heat treatments above 1300u000b0;C because of Ga evaporation during the heat treatment. The Ga-poor state near the surface of the 1450u000b0;C heat-treated specimen was confirmed by electron probe micro-analysis measurements. The electrical resistivity of LTG single crystals decreased by heat treatment in the range of 1000u000b0;C to 1200u000b0;C for 10 h in air, where no precipitation was observed, whereas the resistivity increased with heat treatment over 1400u000b0;C for 10 h in air. The electrical resistivity of the Ga-poor surface region was higher than that of the interior.}