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

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 Zr 2 SP 2 O 12 , which has unique negative thermal expansion behavior involving both mechanisms. Zr 2 SP 2 O 12 undergoes a framework-type mechanism at temperatures 453 K and an isosymmetric phase transition at 393–453 K. The volumetric CTE of α-Zr 2 SP 2 O 12 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-Zr 2 S 0.9 P 2 O 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-Zr 2 S 0.9 P 2 O 12 − δ is reduced by ~1.3%. Finally, this paper presents methods for the hydrothermal synthesis of α-Zr 2 SP 2 O 12 and for controlling the sulfur content. Composites: More than one way to control overheating An unusual crystal that shrinks in response to heat can help avoid damage to composite materials, such as computer chip components, facing unexpected temperature changes. While most atoms tend to move apart as a crystal is warmed up, in negative thermal expansion materials the atoms move closer together. Toshihiro Isobe and colleagues from the Tokyo Institute of Technology in Japan report a method for synthesizing an oxide containing zirconium, sulfur, and phosphorus that exhibits two distinct mechanisms of negative thermal expansion. This oxide undergoes a crystal phase change that provides a large shrinking effect within a narrow temperature range. The crystal is capable of smaller contractions through a broader heating span through atomic framework rearrangements. These variable properties make it easier to fine-tune thermal expansion effects to meet specific applications. Zr 2 SP 2 O 12 has unique negative thermal expansion behavior involving both phase transition- and framework-type mechanisms. The volumetric CTE of α-Zr 2 SP 2 O 12 is approximately −70 ppm/K during the isosymmetric phase transition in the temperature range of 393–453 K. This value can be improved by decreasing the proportion of sulfur. The minimum volumetric CTE of α-Zr 2 S 0.9 P 2 O 12-δ is approximately −108 ppm/K.