Negative thermal expansion in α-Zr2SP2O12 based on phase transition- and framework-type mechanisms

Abstract Materials with negative coefficients of thermal expansion (CTEs) can be used to prepare composites with specific CTE values. Negative thermal expansion behavior can be primarily attributed to two types of mechanisms: phase transition- and framework-type mechanisms. This paper reports Zr₂SP₂O₁₂, which has unique negative thermal expansion behavior involving both mechanisms. Zr₂SP₂O₁₂ undergoes a framework-type mechanism at temperatures <393 K or >453 K and an isosymmetric phase transition at 393–453 K. The volumetric CTE of α-Zr₂SP₂O₁₂ is ~−70 p.p.m./K during the isosymmetric phase transition, and this value can be decreased by decreasing the proportion of sulfur. The minimum volumetric CTE of α-Zr₂S_0.9P₂O_12-δ is ~−108 p.p.m./K in the temperature range of 393–453 K. Between 303 and 773 K, the volume of α-Zr₂S_0.9P₂O_{12 − δ} is reduced by ~1.3%. Finally, this paper presents methods for the hydrothermal synthesis of α-Zr₂SP₂O₁₂ and for controlling the sulfur content.