Transitions between P21, P63 (√ 3A), and P6322 modifications of SrAl2O4 by in situ high-temperature x-ray and neutron diffraction

Abstract

The results of in situ high-temperature X-ray and neutron powder diffraction experiments reconcile inconsistencies in previous reports on the symmetry of high-temperature phases of SrAl2O4. The material undergoes two reversible phase transitions P21↔P63(3A) and P63(3A)↔P6322 at ∼680 and ∼860°C, respectively, and the latter one is experimentally observed and characterized for the first time. The higher symmetry above the P63(3A)↔P6322 transition is gained by disordering off-center split site of oxygen atoms around trigonal axis rather than by unbending Al–O–Al angle to the ideal value 180°. The analysis of the literature suggests that it is a common feature of the P6322 phases of stuffed tridymites.© 2007 Elsevier Inc.