Phase Transformations of Baddeleyite induced by Compression

Baddeleyite. whose composition is denoted as ZrO_2. is found in rocks of roxenite or syenite。Its crystal symmetry is classified as monoclinic。No other allotropy has been known in nature。此材料具有two high temperature和two high pressure polyymorphs。四角形和立方体.和Ortho（I）和（II）尊重.这个物质.已知在zirconia的名称下.拥有实际上有用的性质，如高强度和分形困难.这些在相位之间的相互关系上有很强的依赖性.要承诺这些特征.不公正-掺杂的物质.为什么要稳定成为高温形式之一.现在在技术应用中流行.在这个项目中.高温度的稳定领域压力相位和由压缩被调查产生的相位转换机制。作为Ortho（I）相位，它的存在并不清楚，因为它的结构在1个大气压上无法维持，目前的实验成功进入了这个相位。 ... More 当ZrO_2的良好启动粉末被准备好，在类似的处理中，Ortho （I）阶段剂量为2mol%Y_2O_3的ZrO_2也是可靠的，但在四个阶段中也是原始的，在启动粉末中始终一致存在的，总是在产品中找到。这是由考虑到Ortho稳定性的事实解释的。而四个相位相对于压缩几乎是相同的，并且在压力释放后，在这两个相位之间的密度差异较小的情况下，这两个相位之间的晶体结构（I）相位是由Rietveld分析确定的。确认在压力下是相同的。Ortho（II）两个ZrO_2和2mo1%Y_2O_3在1000 C和10 GPa以上条件下合成的。产品的Rietveld分析显示，它是与cotunnite相同的结构。在Y_2O_3-情况下发现了一种特殊现象。从压力中被抑制的样品略微低于10 GPa。产品只包含单线性相位，但不是四角相位（I）被观察的。这可能是四角相位变为压缩接近10 GPa而转向Ortho（I）的机制。也已经看到了。Ortho（I）在减压压力下，相位是不稳定的，只有单色相位可以在治疗样本中找到。Less（低）

Baddeleyite.whose composition is denoted as ZrO_2.is found in rocks of pyroxenite or syenite.Its crystal symmetry is classified as monoclinic.No other allotropy has been known in nature.This material has two high temperature and two high pressure polymorphs. tetragonal and cubic.and Ortho(I)and(II)respectively.This substance.known under the name zirconia.possesses practically useful properties such as high strength and fracture toughness.These are strongly depend on the interrelations among the phases mentioned above.To promote these peculiarities.impurity-doped substances.which are stabilized to be one of high temperature forms.are now popular in technological applications.In this project.the stability fields of high pressure phases and a mechanism of phase transformation generated by compression have been investigated.As for Ortho(I)phase.its existence had not been clear since its structure was difficult to be maintained at 1 atm.The present experiment succeeded to quench this phase … More when fine starting powder of ZrO_2 was prepared.In the similar processing.Ortho (I)phase of 2 mol%Y_2O_3 doped ZrO_2 was also quencheable but the tetragonal phase.which had originally coexisted in the starting powder.was always found in the product.This is explained by considering a fact that the stability of Ortho(I)and the tetragonal phases against compression is almost same and the latter survives after the removal of pressure since the difference in density between these two phases is small.The crystal structure of quenched Ortho(I)phase was refined by the Rietveld analysis.being confirmed to be the same as that determined under pressure.Ortho(II)phases of both ZrO_2and 2 mo1%Y_2O_3were synthesized under conditions above 1000゜C and 10GPa.The Rietveld analysis of the product showed that it is isostructural with cotunnite.A peculiar phenomena were found in the case of Y_2O_3-doped sample depressed from pressures slightly below 10GPa.The product only consisted of the monoclinic phase but neither Ortho(I)nor the tetragonal was observed.This is probably due to a mechanism in which the tetragonal phase becomes unstable by compression close to 10GPa and turns to Ortho(I).As is already seen.Ortho(I)phase is unstable on decreasing pressure and the only monoclinic phase is found in the treated samples. Less