Characterization of the negative thermal expansion material Zr1—xHfxW2O8

The oxide ZrW2Osdisplays unusual property of isotropic negative thermal expansion in a large wide temperaturerange, which makes it have a number of important potential applications. The cubic Zrl-xHfxW2O8 (x = 0, 0.3, 0.5, 0.7, and1.0) weresynthesized by standard solid state reaction technique. The high and low temperature X-ray diffraction analysisindicate that the substitution of the Hf4+ for Zr4+ only leads to reducing the lattice constants, and the changes of negativethermal expansion coefficients are not obvious. The linear expansion coefficients of Zrl-xHfxW2O8 (x = 0, 0.3, 0.5, 0.7, and1.0) are about -6 × 10-6 K-1 in the temperature range of 298 to 973 K, while that of Zr0.5Hf0.5W2O8 is -9.6 × 10-6 K-1 from83 to 298 K. The phase transition temperatures from α-ZrW2O8 to β-ZrW2O8 structure were also determined by X-ray dif-fraction method. Thermogravimetric analysis (TGA) exhibits that Zrl-xHfxW2O8 is not hygroscopic in air.