Calorimetric and Raman Studies on Negative Thermal Expansion Materials Zr_1-xHf_xW₂O₈ Solid Solutions

抄録

ZrW₂O₈ has received considerable attention in recent years, because of its isotropic negative thermal expansion over a wide temperature range from 0.3 to 1050 K. The negative thermal expansion of ZrW₂O₈ is attributed to the complex crystal structure, which consists of ZrO₆ octahedra and WO₄ tetrahedra, sharing the oxygen atoms at the vertexes of the polyhedra each other. It is widely accepted that the low-energy vibrations of the ZrO₆ and WO₄ polyhedra cause the negative thermal expansion of ZrW₂O₈. The phonon properties of Zr_1-xHf_xW₂O₈ were characterized by using calorimetric and Raman techniques, in order to investigate the low-energy vibrations of the polyhedra. The low-energy vibrations of the octahedra strongly depended on a kind of the center cation. We will discuss the phonon properties of the solid solutions.