Characterization of the negative thermal expansion material Zr_(1-x)Hf_xW_2O_8

摘要

The oxide ZrW_2O_8 displays unusual property of isotropic negative thermal expansion in a large wide temperature range, which makes it have a number of important potential applications. The cubic Zr_(1-x)Hf_xW_2O_8 (x = 0, 0.3, 0.5, 0.7, and 1.0) were synthesized by standard solid state reaction technique. The high and low temperature X-ray diffraction analysis indicate that the substitution of the Hf~(4+) for Zr~(4+) only leads to reducing the lattice constants, and the changes of negative thermal expansion coefficients are not obvious. The linear expansion coefficients of Zr_(1-x)Hf_xW_2O_8 (x = 0, 0.3, 0.5, 0.7, and 1.0) are about -6 x 10~(-6) K~(-1) in the temperature range of 298 to 973 K, while that of Zr_(0.5)Hf_(0.5)W_2O_8 is -9.6 x 10~(-6) K~(-1) from 83 to 298 K. The phase transition temperatures from α-ZrW_2O_8 to β-ZrW_2O_8 structure were also determined by X-ray diffraction method. Thermogravimetric analysis (TGA) exhibits that Zr_(1-x)Hf_xW_2O_8 is not hygroscopic in air.