Structures and Phase Transitions in Rb₂MoO₄ and Rb₂WO₄

Abstract

The structural phase transitions of Rb₂MoO₄ and Rb₂WO₄ have been reinvestigated with the use of heat capacity measurement and synchrotron X-ray and neutron scattering techniques. In Rb₂MoO₄, the existence of polymorphous structures has been confirmed. These crystal structures at 290 K are a monoclinic β-K₂MoO₄ type one and an orthorhombic β-K₂SO₄ type one. In an annealed sample, two typical first-order-type anomalies were observed at 783 and 752 K. Furthermore, new λ-type anomaly equivalent to the second normal-incommensurate phase transition in A₂BO₄-type ferroelectrics was observed at 223 K. On the other hand, the crystal structure at 290 K of Rb₂WO₄ was a monoclinic β-K₂MoO₄ type one and no phase transition was detected down to 8 K.

Keywords:

• Rb₂MoO₄
• Rb₂WO₄
• structural phase transition
• structural analysis

Acknowledgment

The present work was partly supported by the collaborative research project of Materials and Structures Laboratory, Tokyo Institute of Technology, and by a research grant from the Yamaguchi University Foundation.