A neutron powder investigation of the high-temperature phase transition in NiTiO3
A neutron powder investigation of the high-temperature phase transition in NiTiO3
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NiTiO3 高温相变的中子粉研究
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
T. Vogt
中科院分区：
文献类型：
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作者：
H. Boysen;F. Frey;M. Lerch;T. Vogt
用中子粉末衍射法跟踪了NiTiO3在1650K温度下的相变结构变化。在Tc 1560 K时，它从（有序的）钛铁矿结构（R3）转变为具有随机分布的阳离子的无序的类钛铁矿结构（R3c）。详细的Rietveld细化，包括非谐和分裂原子模型表明，过渡过程是不是一个简单的直接交换两个相邻的阳离子。每种阳离子物质在其实际氧八面体中占据其自己的特定位置。一些间隙阳离子密度是圆的，但仅在有限的温度区域内。这被分配到温度依赖的迁移率或阳离子。进一步考虑温度的变化或各种界面窗口和四面体和八面体空腔的大小，推导出了一个基元交换过程。概述了在存在（非谐）原子密度分布时，确定原子占据数和位置（跃迁序参量）的困难
The structural changes at the phase transition in NiTiO 3 have been followed by neutron powder diffraction up to 1650 K. At T c 1560 K it transforms from an (ordered) ilmenite structure (R3) to a disordered corundum like structure (R3c) with a random distribution of the cations. Detailed Rietveld refinements including anharmonic and split-atom models revealed that the transition process is not a simple direct interchange of two neighboring cations. Each cation species occupies its own specific position in its actual oxygen octahedron. Some interstitial cation densities are round, but only in a limited temperature region. This is assigned to temperature dependent mobilities or the cations. Taking into account further the temperature variation or the sizes or various interfacial windows and tetrahedral and octahedral cavities an elementary exchange process is deduced. The difficulties in defining atomic occupancies and positions (the order parameters of the transition), when (anharmonic) atomic density distributions are present, are outlined