摘要:
X-ray diffraction, DTA and Raman scattering experiments on powder and single crystals have been carried out to study the structure and phase transitions of MeNH(3)GeCl(3). The compound crystallizes in an orthorhombically distorted perowskite structure and undergoes two phase transitions at 348K and 403K into a rhomboedric HT1 and finally a cubic HT2 modification. On cooling down to 10K, no further symmetry reduction was detectable. The Raman spectra show that the HT-phases are disordered. Assignments for the vibration bands and calculated force constants are given. The HT1-phase is isostructural to RT-CsGeCl3 which shows discontinuities of the dielectric constant at the transition to the cubic structure. In order to quantify the lone pair activity of Ge(II), bond valences were calculated for several compounds AGeCl(3). (A-monovalent cation; e.g. Cs, MeNH(3)).