The powders were synthesised by the conventional ceramic process: wet mixing of raw
materials in distilled water, drying in oven at 105 8C overnight, pulverisation in agate mortar, then calcination in
alumina crucibles in an electric kiln in static air at maximum temperature of 1400 8C, with thermal rate of 200 8C/h,
soaking time of 4 h and natural cooling to room temperature.