Structural, thermal behavior, vibrational study and superprotonic behavior of a new rubidium dihydrogen phosphate-arsenate: RbH2(PO4)0.65(AsO4)0.35

Abstract The structural characteristics of the crystals (RbH 2 (PO 4 ) 0.65 (AsO 4 ) 0.35 ) were analyzed by means of X-ray diffraction, which revealed that the new title compound is nearly isomorphous with the tetragonal phase of RbH 2 AsO 4 (RDA). The following results have been obtained: space group I −  42d , a = 7.6837 (8) A , c = 7.3824 (19) A , V = 435.85(13) A 3 and Z = 4. The phosphorus and the arsenic atom as well as the rubidium ions lie on points with site symmetry S 4 , the oxygen atoms lie in general positions about the phosphorus–arsenic atoms, in a tetrahedral arrangement. The (P/As)O 4 tetrahedra are connected by O H…O hydrogen bonds laying essentially in the a,b plane. Differential scanning calorimetric traces show three phase transitions at 229, 390 and 580 K in this material. Moreover, protonic conduction of the mixed compound determined by impedance and modulus spectroscopy has been studied in the temperature range 150–450 K in order to determine the nature of the phase transition.