Speaker
Description
Rare-earth aluminates (LaAlO3 and GdAlO3) and their calcium-substituted derivates (La1-xCaxAlO3-δ; x = 0.05, 0.10, 0.15 and 0.20; 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. In the case of mechanochemical formation of the GdAlO3, the 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 different porosity of the samples, i.e. dense LaAlO3 and relatively porous GdAlO3 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 ca 350-1000°C in air. Acceptor-type substitution of lanthanum and 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 = 0.05-0.15/0.20. Grain boundaries are demonstrated to have a significant contribution to the total resistivity of prepared calcium-substituted ceramics with grain sizes in the range up to 1.5 μm.
