PROPERTIES OF LACO1-TCRTO3 .1. SOLID SOLUBILITY, THERMAL-EXPANSION AND STRUCTURAL TRANSITIONS

Samples of LaCol-tCrrO3 were prepared with high compositional resolution for 0.00 less than or equal to t less than or equal to 1.00 and were characterized by powder X-ray diffraction (PXD), differential scanning calorimetry (DSC) and infrared (FTIR) spectroscopy. LaCol-tCrtO3 exhibits complete solid solubility. At room temperature the structure is distinctly rhombohedral for t < 0.76 and orthorhombic for t > 0.84. The extension of the implicit two-phase field within the thus established conversion region, 0.76 less than or equal to t less than or equal to 0.84, could not be determined. In the investigated temperature range (120-1200 K) the transition from the low-temperature orthorhombic to high-temperature rhombohedral phase occurs for t greater than or equal to 0.70, the temperature of the transition increasing with increasing t. In the vicinity of the transition, the volume per formula unit is larger for the orthorhombic than for the rhombohedral phase. Thermal expansion coefficients decrease with increasing t, the change being subtle for t less than or equal to 0.60 and more pronounced for t > 0.60. In IR spectroscopy the main feature is a shift of the absorption bands towards higher wavenumbers with increasing t up to t = 0.60, while the wavenumbers are more or less constant for t greater than or equal to 0.75. At t approximate to 0.60 a splitting of certain IR bands also occurs. The parallel changes in properties considered in this study at t approximate to 0.60 suggest that there may be a change in bonding characteristics around the stated value of the composition variable.