单相Ce_(0.5)Zr_(0.5)O_2立方固溶体的高压高温合成

Synthesis of Single phase Cubic Ce_(0.5)Zr_ (0.5)O_2 Solid Solution under High Pressure and High Temperature

以化学沉淀法制备的 Ce O2 和 Zr O2 纳米微粒为前驱体 ,首次在高压高温 (3 .1 GPa,1 0 73 K)下合成了单相 Ce0 .5Zr0 .5O2 面心立方固溶体 .使用 X射线衍射、TG-DTA、XPS、Raman、电子自旋共振谱和交流阻抗谱等对样品的结构、Ce离子的价态和导电性进行了表征 .实验结果表明 ,纳米 Ce O2 -50 % Zr O2 混合物在高压 (0 .9GPa以上 )高温 (1 0 73 K以上 )条件下可以发生固态反应 ,高压下固溶温度明显降低 .Ce0 .5Zr0 .5O2 面心立方固溶体在 773 K以下是热稳定的 ,不发生结构转变 ,固溶体中 Ce离子完全以 Ce4 + 形式存在 ,773 K退火也不引起 Ce4 + 向 Ce3 + 转变 ,晶格中氧缺位非常少 .Ce0 .5Zr0 .5O2 面心立方固溶体是离子导电 ,82 3 K时电导率 σ=1 .2× 1 0 -5S/cm,与纯 Ce O2 在同温度下的电导率同数量级 ;1 1 2 3 K时 σ=2 .1× 1 0 -3 S/cm,小于掺入稀土或碱土氧化物的氧化锆和氧化铈基电解质的电导率 .在高温区和低温区 ln(σT)与 1 /T的关系满足斜率不同的二条直线 ,低温活化能小于高温活化能 .固溶体的显微硬度 (50 g载荷 )为 572 HV.

Using nanoparticles of CeO 2 and ZrO 2 prepared by chemical precipition method as the starting materials, the single phase cubic Ce 0.5 Zr 0.5 O 2 solid solution has been synthesized under high pressure and high temperature for the first time. The structural characteristics and valence state of the single phase cubic Ce 0.5 Zr 0.5 O 2 solid solution were investigated by XRD, TG DTA, Raman, XPS and EPR measurements. The XRD results showed that the nanocrystalline mixtures of CeO 2 50% ZrO 2 can form a cubic Ce 1- x Zr x O 2 solid solution above 1.67 GPa and above 1 073 K, but the product is in a mixture state. The single phase cubic Ce 0.5 Zr 0.5 O 2 solid solution can be obtained only under the certain conditions of 3.1 GPa at 1 073 K. The high pressure promotes the process of the solid state reaction and the temperature of forming CeO 2 ZrO 2 solid solution decreases under high pressure. The DTA curve of the single phase cubic Ce 0.5 Zr 0.5 O 2 solid solution showed a broad exothermic peak between 403 K and 742 K. But the XRD pattern and Raman spectra displayed that the structure of the solid solution had not been changed before and after annealing at 773 K for 1 h. It revealed that the cubic Ce 0.5 Zr 0.5 O 2 solid solution was stable in structure below 773 K. The EPR spectra recorded at room temperature gave an evidence of the presence of Ce 3+ and O 2- in CeO 2 nanoparticles. However, the signals of Ce 3+ and O 2- have not been detected in Ce 0.5 Zr 0.5 O 2 solid solution. An unknown signal( g = 1.990) has been observed in cubic Ce 0.5 Zr 0.5 O 2 solid solution which has not been changed after annealing at 773 K for 1 h, exhibiting that there exists no Ce 3+ in cubic Ce 0.5 Zr 0.5 O 2 solid solution and the Ce 4+ has not been reduced into Ce 3+ after annealing. The hyperfine structure in Zr 3 d XPS spectrum has been observed for the Ce 0.5 Zr 0.5 O 2 solid solution. It shows that there may exist some Zr ions with a low valence state. The ionic conductivity measured by impedance spectroscopy showed that the cubic Ce 0.5 Zr 0.5 O 2 solid solution exhibits only the bulk conductivity. The bulk conductivity( σ= 1.2× 10 -5 S/cm at 823 K, σ =2.1×10 -3 S/cm at 1 123 K) is the same as that of CeO 2, but smaller than that of Y 2O 3 stabilized ZrO 2. A marked curvature at T =823 K has been observed in the Arrhenius plot of the bulk conductivity. The activation energy below 823 K is lower than that above 823 K, and the reason has been discussed.