Zr_(1-x)Hf_xW_2O_8的合成及负热膨胀特性的研究

Negative Thermal Expansion of Zr_(1-x)Hf_xW_2O_8

采用固相化学反应的方法 ,成功合成了立方结构的Zr1 -xHfxW2 O8(x =0 ,0 3 ,0 5 ,0 7,1 0 )系列材料。X射线衍射结果表明 ,Hf4 +能替代Zr4 +形成二元固溶体 ,固溶体的晶胞参数与体积随着Hf4 +含量x的增加而降低。采用高、低温X射线衍射的方法测定晶胞参数和体积随温度的变化关系 ,结果表明 :Zr1 -xHfxW2 O8化合物在实验温度范围具有强烈的负热膨胀效应 ,但其负热膨胀系数不随Hf4 +含量x变化。在2 98～ 973K ,Zr1 -xHfxW2 O8线膨胀系数αl 约为 -6× 10 - 6 K- 1 ;在 83～ 2 98K ,Zr0 5Hf0 5W2 O8的αl=-9 6× 10 - 6 K- 1 。变温XRD研究还表明 ,Zr1 -xHfxW2 O8化合物从α ZrW2 O8相向 β ZrW2 O8相的转变温度随Hf4 +含量x的增加而略有升高 ,热重分析 (TGA )研究结果表明 ,Zr1 -xHfxW2

The cubic compounds Zr 1- x Hf x W 2O 8( x =0, 0 3, 0 5, 0 7, 1 0) were synthesized by standard solid state reaction technique The high and low temperature X ray diffraction results indicate that the substitution of the Hf 4+ for Zr 4+ reduces the lattice constants only but has not obvious effect on the negative thermal expansion coefficients The linear thermal expansion coefficient of Zr 1- x Hf x W 2O 8 (x =0, 0 3, 0 5, 0 7, 1 0) is about -6×10 -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 6×10 -6 K -1 from 83 to 298 K X ray diffraction results also exhibit that the phase transition temperature from α ZrW 2O 8 to β ZrW 2O 8 structure increases as the x increases Thermogravimetric analysis (TGA) shows that Zr 1- x Hf x W 2O 8 is not a water absorbed ceramic in air