Mechanosynthesis and electrical conductivity of undoped and calcium-substituted GdAlO3 perovskites

Abstract

Gadolinium aluminate (GdAlO3) and its calcium-substituted derivates (Gd1-xCaxAlO3-δ; x = 0.05, 0.10 and 0.15) are prepared via one-step mechanochemical processing of simple oxide precursors at ambient temperature. The mechanochemical reaction is accompanied by Gd2O3 phase transformation. The as-prepared and sintered materials are characterized by X-ray diffraction and scanning electron microscopy. Sintering at 1450°C resulted in relatively porous ceramics (with density <90% of theoretical value) except Gd0.85Ca0.15AlO3-δ. The electrical conductivity of the sintered samples was investigated by impedance spectroscopy at 350-1000°C in air. Undoped GdAlO3 ceramics exhibit low conductivity, ~10-6 S/cm at 800°C. Acceptor-type substitution of 5 at.% of gadolinium by calcium results in ~3 orders of magnitude increase in both total and bulk conductivity associated with a substantial enhancement in oxygen-ionic transport. Further doping has a limited effect on the electrical transport properties, and electrical conductivity remains nearly composition-independent in the range x = 0.05-0.15. Grain boundaries are demonstrated to have a significant contribution to the total resistivity of prepared calcium-substituted Gd1-xCaxAlO3-δ ceramics with grain sizes in the range of 1.1-1.5 μm.