X-ray and neutron investigations on the intermediate phase of the CA-W04 aluminate sodalite CAW

Abstract

The intermediate phase of the aluminate sodalite Ca₈[Al₁₂O₂₄](WO₄)₂, stable between 653 and 617 K, has been studied by X-ray single crystal, X-ray powder and neutron powder methods, and its structure determined. The phase is difficult to detect by diffraction methods, mainly because of its similarity with the cubic phase with only weak superstructure reflections distinguishing both phases. From the combined studies the following main features of the i-phase emerged: P4c2, a = 13.1692(7), c = 9.301(1)Å (neutrons), spontaneous strain at least an order of magnitude smaller than in the room-temperature phase, disordered WO₄ groups, positional modulation of the Ca cations.

Key Words:

• Aluminate sodalites
• phase transitions
• intermediate CAW