In situ high-temperature synchrotron radiation powder diffraction patterns were taken from room temperature to T = 740°C from synthetic feldspars along the join CaAl2Si2O8–SrAl2Si2O8 (An–SrF). Three samples of composition An95SrF5, An90SrF10 and An85SrF15 were investigated, and the evolution of cell parameters with T was determined by Rietveld analysis of powder X-ray diffraction patterns. The high-temperature P[`1]\text-I[`1]P1-I1 phase transition, previously observed with Tc = 241°C in anorthite, was found in An95SrF5, An90SrF10 and An85SrF15 feldspars at Tc = 233(5)°, 195(2)° and 174(2)°C respectively. The transition was revealed by the disappearance of critical reflections and variations in the rate of change of cell parameters with temperature. A significant, although small (between 0.0025 and 0.0012 at room temperature), spontaneous strain could be measured, allowing the thermodynamic behaviour of the transition to be modelled. A second-order trend for An90SrF10 and An85SrF15 [P[`1]P1 phase is An60SrF40.
Tribaudino, M., Benna, P., Nestola, F., Meneghini, C., Bruno, E. (2005). Thermodynamic behaviour of the high temperature P -I phase transition along the CaAl_2Si_2O_8-SrAl_2Si_2O_8 join. PHYSICS AND CHEMISTRY OF MINERALS, 32, 314-321 [10.1007/s00269-005-0469-4].