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Phase Transformations of Baddeleyite induced by Compression

压缩诱导斜锆石的相变

基本信息

批准号：
61460057
负责人：
KUME Shoichi
金额：
$ 2.75万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

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

斜锆石（Baddeleyite），其成分记为ZrO_2，产于辉石岩或正长岩中，晶体对称性属单斜晶系，自然界中未见其它同素异形体。该物质有两种高温和两种高压多晶型。四氧化锆和立方氧化锆，以及邻位氧化锆（Ⅰ）和（Ⅱ）。这种物质，以氧化锆的名称为人所知，具有实际有用的性质，如高强度和断裂韧性。这些性质在很大程度上取决于上述相之间的相互关系。为了促进这些特性，杂质-掺杂物质的高温稳定性是目前技术应用中的一个热点，在本项目中，本文研究了压缩相和压缩相变的机理.对于邻位（Ⅰ）相，由于其结构在1个大气压下难以保持，其存在一直不清楚.本实验成功地淬灭了该相 ...更多信息在制备ZrO_2细粉的过程中，掺2mol%Y_2O_3的ZrO_2原粉中的邻（I）相也是可淬的，但原粉中共存的四方相却始终存在于产物中，这是由于邻（I）相的稳定性受到了影响。四元相对压缩的抵抗力几乎相同，并且由于这两相之间的密度差很小，四元相在压力去除后仍然存在。在1000 ℃以上和10 GPa的条件下，合成了ZrO_2和2mo1%Y_2O_3的邻位（Ⅱ）相。产物的Rietveld分析表明，它与钴钨石是同构的。在Y_2O_3-ZrO_2的情况下，发现了一种特殊的现象。掺杂样品在压力略低于10 GPa时降压，产物仅由单斜相组成，但没有观察到邻位（I）和四位（I）。这可能是由于四位（I）相在压力接近10 GPa时变得不稳定并转变为邻位（I）的机制所致。相在减压下不稳定，在处理过的样品中发现唯一的单斜相。少