Paul F. Schofield, Andrew J. Berry, Patricia M. Doyle, Kevin S. Knight
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引用次数: 0
摘要
CaAl12O19 能以 Ti3+ 和 Ti4+ 的形式结合 Ti（与 Mg2+ 电荷耦合置换），是最早从太阳成分气体中凝结出来的矿物之一，可用作陶瓷。它有不同的名称，如希波石、六铝酸钙（CaO.6Al2O3）和 CA6。通过中子粉末衍射法测定了 CaAl11.8Ti3+0.2O19 和 CaAl9.8Ti3+0.54Mg0.83Ti4+0.83O19 式中 Ti 取代的希波石（P63/mmc）的晶格参数和单胞体积与 ~ 10 至 275 K 温度的函数关系。两种化合物的 a 变化大致相等，而 CaAl11.8Ti3+0.2O19 的 c 变化几乎大 50%。CaAl11.8Ti3+0.2O19 在 10 至 70 K 之间也表现出负热膨胀。两种成分的单位晶胞体积随温度的变化可以用爱因斯坦的两式表达式很好地描述。c 的巨大变化与 Ti 被置换到 R 块结构单元的 M2 和 M4 位点是一致的。
CaAl12O19, which can incorporate Ti as both Ti3+ and Ti4+ (charge coupled substitution with Mg2+), is one of the first minerals to condense from a gas of solar composition and is used as a ceramic. It is variously known as hibonite, calcium hexaluminate (CaO.6Al2O3), and CA6. The lattice parameters and unit cell volumes of Ti-substituted hibonite (P63/mmc) with the formulae CaAl11.8Ti3+0.2O19 and CaAl9.8Ti3+0.54Mg0.83Ti4+0.83O19 were determined as a function of temperature from ~ 10 to 275 K by neutron powder diffraction. The thermal expansion is highly anisotropic with the expansion in c a factor of ~ 5 greater than that in a. The change in a is approximately equal for the two compounds whereas the change in c is almost 50% larger for CaAl11.8Ti3+0.2O19. CaAl11.8Ti3+0.2O19 also exhibits negative thermal expansion between 10 and 70 K. The change in unit cell volume with temperature of both compositions is well described by a two term Einstein expression. The large change in c is consistent with substitution of Ti onto the M2 and M4 sites of the R-block structural unit.
期刊介绍：
Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are:
-Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.)
-General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.)
-Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.)
-Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.)
-Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems
-Electron microscopy in support of physical and chemical studies
-Computational methods in the study of the structure and properties of minerals
-Mineral surfaces (experimental methods, structure and properties)
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