Development of Negative Thermal Expansion Material Utilizing Structural Phase Transition of Zn₂P₂O₇

Abstract

Large negative thermal expansion (NTE) was achieved at room temperature using the structural phase transition in Zn₂P₂O₇. Particularly, Zn_1.6Mg_0.4P₂O₇ has a negative coefficient of linear thermal expansion αL of about –60 ppm/K at temperatures of 289–374 K. Co-doping of Mg and another element at the Zn site was found to be effective for control of NTE properties and for improvement of thermal expansion compensating ability. The present phosphates are expected to have widely various practical applications as thermal expansion compensators because they contain no toxic or expensive elements. Moreover, they can be prepared using a simple solid-state reaction method in air.