The double-peak phenomenon of the phase transition of Rb substituting K in LiKSO4, competition between Rb sub-lattice and smearing the phase transition

The influence of Rb in the triple sulfate LiK(1−x)RbxSO4 (0 ≤ x ≤ 0.2) compound on the structural and thermal properties of the bulk material is discussed. Samples were prepared by fusing the sulfates in stoichiometric ratios in a platinum crucible at 1273 K for 30 min. The x-ray powder diffraction measurements were performed at ambient temperature. The crystal structure parameters were refined by the Rietveld method using the FullProf program. The analysis indicated a single-phase having a hexagonal symmetry with space group P63 regardless of the Rb content. Thermal analysis by differential scanning calorimetry shows a considerable shift of the phase transition point towards lower temperatures with increasing Rb content. A pre-transitional effect is observed by differential thermal analysis of the sample without Rb contribution while for the sample with 20% Rb the transition is represented by double endothermic peaks. The energy of transition has been estimated using the Kissinger method for samples with different concentrations of Rb.