Influence of the growth method upon the phase transition of RbCdCl $\mathsf{_{3}}$

Structural properties of two RbCdCl₃ samples grown either from the melt or from aqueous solution are studied via X-ray diffraction over a closed temperature cycle between 20 C and 300 C. During cooling step (300 C), the crystal grown from the melt undergoes a phase transition at 110 C that drives it from the cubic structure into a tetragonal structure that still persists at 20 C. It undergoes exactly the reverse phase transition at the same temperature during the heating ( C) step that immediately follows. The other crystal grows from aqueous solution at 20 C in an orthorhombic structure (i.e. not tetragonal as that of the crystal grown from the melt and cooled down to this temperature). During the heating ( C) step, it undergoes a direct orthorhombic-cubic phase transition at 240 C (without passing through the tetragonal phase) whereas, during subsequent cooling (300 C), it does not exhibit the corresponding reverse phase transition but rather exhibits exactly the same cubic-tetragonal phase transition at 110 C as the crystal grown from the melt. However, for both crystals, this tetragonal phase observed at room temperature is unstable and slowly converts into an orthorhombic phase over the course of time. Complementary Differential Scanning Calorimetry (D.S.C.) and Thermo Gravimetric Analysis (T.G.A.) measurements have been carried out over the range ( ) C in order to interpret diffraction experiments.Received: 19 May 2004, Published online: 30 September 2004PACS: 61.10.Nz X-ray diffraction - 64.70.Kb Solid-solid transitions - 65.40.Ba Heat capacity