Negative thermal expansion in a zirconium tungstate/epoxy composite at low temperatures

We have investigated a composite of cubic α-ZrW₂O₈ and epoxy with a high ceramic loading for its thermal expansion properties at cryogenic temperatures. The composite was fabricated by allowing the ceramic to sediment in the epoxy resin before curing, using only the dense bottom fraction of the composite for further measurements. Density measurements and thermogravimetric analysis showed that the samples repeatably consisted of approximately 60 vol% tungstate without significant voids. The coefficient of thermal expansion was measured by dilatometry at temperatures from 25 to 300 K, and we found negative thermal expansion occurring at temperatures below about 100 K. The observed behavior is consistent with predictions produced by a variational model, which shows that the high ceramic loading is necessary to reliably achieve negative thermal expansion in the composite. The composite has potential applications as compensators for unwanted thermal expansion at low temperatures and for fiber-optic cryogenic temperature sensors.