Synthesis,Characteristics And Property Of Negative Thermal Expansion Solid Solutions

Negative thermal expansion(NTE),i.e.a decrease in length as temperature increases, Materials which demonstrate NTE can be divided into three classes:isotropic, anisotropic and amorphous.Materials that exhibit negative thermal expansion (NTE) have been of considerable interest, since Sleight et al.reported ZrW2O8 shows NTE in 1996.Due to ZrW2O8′s relatively large isotropic, unusual negative thermal expansion over a wide range of temperature from 0 to 1050k,and Zr cation position could be partly substituted by various cations,the thermal expansion coefficients could be adjusted to a desired value. Rare earth tungstate negative thermal expansion materials in precision instruments manufacturing, aviation,aerospace, marine, communications and other high-technology has an extremely important purposes.Rare earth and tungsten resources are the advantages of our country, to carry out this project for the comprehensive utilization of resources to promote the advantages of positive significance.Synthesis and properties of negative thermal expansion materials Zr1-XLaXW2O8-X/2 substituted for Zr(IV) sites by the heavy rare earth ions have been recently reported while no paper has been written on the preparation of Zr1-XLaxW2O8-X/2 (M was lighter rare earth ions).Firstly, the synthesis of ZrW2O8 were reported.The products were characterized by X-ray powder diffraction and scanning electric microscope.Secondly, Synthesis and properties of negative thermal expansion materials Zr1-XLaXW2O8-X/2 substituted for Zr(IV) sites by the light rare earth ions were reported. The structure and morphology of the resulting powders were characterized by powder X-ray diffraction (XRD) and scanning electron microscope(SEM) respectively. The thermal expansion coefficient of the samples were measured by dilatometer at room temperature to 700℃.The results showed that samples were single cubic phase.The average thermal expansion coefficients of ZrW2O8 Zr0.99La0.01W2O7.995 and Zr0.98La0.02W2O7.99 were-2.594×10-6K-1,-2.309×10-6K-1,and-2.298×10-6K-1 in the temperature range from room temperature to 200℃,-5.002×10-6K-1,-4.810×10-6K-1, and-4.730×10-6K-1 from 200℃to 700℃respectively. The phase transition temperature of the samples were between 150℃to 220℃.There were slightly decrease in the thermal expansion property of the samples with the increase in substitution fraction X.