The mixture was then combined with either MgCl2 or KCl in the weight ratio of 1/4 prior to be contained in an alumina crucible covered with a lid and placed in an alumina tube furnace under a constant flow of argon. The furnace was then heated to a target temperature between 800 and 1200°C at 3°C/min and held for 3 h before being cooled down at the same rate to room temperature. The reacted mass was washed repeatedly with hot distilled water and then subjected to acid leaching with a dilute HCl solution to remove the residual salt and the by-product MgO. The final product powder was oven-dried overnight at 90 °C prior to further characterisation by XRD and SEM.