Polymorph stability and phase transitions of trigonal Al1-xGaxPO4 mixed crystals

Single crystals of Al1-xGaxPO4 of various mole fractions x were grown from phosphoric acid solutions under hydrothermal conditions using the slow-heating method. In order to relate the parameters of this low-quartz structure analogue and the observed phase transitions to the respective mole fraction, the crystals were investigated by means of electron probe microanalysis. X-ray powder diffraction and differential thermal analysis. The results are discussed in terms of the segregation effects occuring during growth. The limiting geometrical parameters for the existence of the high-quartz phase are compared to the values given in the literature.