A model proposed for the interpretation of DTA and X-ray data of the III → I transition in sodium sulfate

Abstract

The transition between phase I and phase III in sodium sulfate (Na 2SO 4) was studied by high temperature X-ray diffraction and the calculation of diffraction patterns. An intermediate phase (phase II) was detected on cooling in the undoped and 1.7 at.% yttrium-doped Na 2SO 4, but not observed in the 3.8 at.% Y-doped sample. The DTA and X-ray diffraction results of the III ↦ I transition were explained well by a proposed model which consisted mainly of the following steps: (i) the rotation of the SO 4 tetrahedra, and (ii)the disappearance of interfaces among the transformed domains.