THE CRYSTAL STRUCTURE AND STRUCTURAL PHASE TRANSITION OF La_(1-x)Ae_xCrO_3 (Ae=Sr, Ca)

摘要

The crystal structure and structural phase transition of L (Ae=Sr, Ca) were investigated with X-ray diffraction at various temperatures, synchrotron x-ray diffraction and differential scanning calorimetry (DSC). The crystal structure of La_(1-x)Ca_xCrO_3 (x=0.0～0.3) and La_(0.95)Sr_(0.05)CrO_3 was orthorhombic-distorted perovskite at room temperature. The first order structural phase transition from the orthorhombic phase to rhombohedral-distorted perovskite was observed at ～245°C in LaCrO_3. The phase transition was observed in La_(1-x)Ca_xCrO_3 (x=0.1～0.3) and its temperature increased with increase of Ca content. The phase transition was also observed in La_(0.95)Sr_(0.05)CrO_3 at ～ 140°C with DSC and X-ray diffraction, however, clear phase transition was not observed in DSC curves of La_(1-x)Sr_xCrO_3 with x≧0. 10. X-ray diffraction measurement revealed that the crystal system of La_(1-x)Sr_xCrO_3 with x≧0.15 at room temperature was rhombohedral-distorted perovskite. It was also revealed that La_(0.90)Sr_(0.10)CrO_3 was a mixture of orthorhombic phase and rhombohedral one at temperature range -100～300°C and that fraction of the rhombohedral one increased with increase of temperature.