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首页> 外文期刊>Philosophical magazine, B. Physics of condensed matter, electronic, optical, and magnetic properties >Metastable magnesium titanate phases synthesized in nanometric systems
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Metastable magnesium titanate phases synthesized in nanometric systems

机译：在纳米系统中合成的亚稳态钛酸镁相

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When heating mixtures of conventional magnesia and titania powders, geikielite (MgO.TiO2) appears first at about 600 degrees C; only above 1200-1300 degrees C is either qandilite (2MgO.TiO2) or karrooite (MgO.2TiO(2)) formed, depending on whether MgO or TiO2 is in excess. A different behaviour pattern is observed when starting from nanometre precursors, consisting of hydroxides of magnesium and titanium, which lose water on heating to about 400 degrees C, yielding nanocrystalline oxides. Coprecipitated nanometre precursors yield at 600 degrees C qandilite, geikielite or karrooite, depending on the relative stoichiometries of magnesia and titania in the precursor powder. At higher temperatures, up to 1200 degrees C geikielite is the only titanate formed, and only above 1300 degrees C does qandilite or karrooite reappear, depending on the stoichiometry of the original mixture. Only karrooite is formed when independently prepared nanometre precursors of magnesia and titania are mixed together and heated to temperatures as low as 400 degrees C and up to 600 degrees C, the stoichiometric ratio of the mixture notwithstanding. Estimation of surface area changes taking place when nanometre particles coalesce with each other to form magnesium titanates show that substantial reductions in surface energy take place, even if the products remain of nanometre size. Such reductions depend on the absolute and relative particle sizes of the reacting oxides and the stoichiometry of the final product. The contribution of diffusion processes, surface energy and misfit volume to the formation of the various magnesium titanates from the oxides is discussed. All three magnesium titanates synthesized from nanometre precursors show a stable dielectric constant epsilon over a wide range of frequencies, in contrast with an equivalent commerical powder used in the manufacture of microcondensers. Furthermore, the quality factor Q of magnesium orthotitanate (geikielite) synthesised from nanometre precursors is higher by about one order of magnitude than that of the commercial product.
机译：当加热传统的氧化镁和二氧化钛粉末的混合物时，首先在约600摄氏度时出现辉石（MgO.TiO2）;然后在约600摄氏度时出现。仅在高于1200-1300摄氏度的温度下，才会形成黄铁矿（2MgO.TiO2）或钾铁矿（MgO.2TiO（2）），具体取决于MgO或TiO2是否过量。当从由镁和钛的氢氧化物组成的纳米前体开始时，观察到不同的行为模式，所述纳米前体在加热至约400℃时会失水，从而产生纳米晶体氧化物。共沉淀的纳米前驱体在600摄氏度下生成轻质锂铁矿，方铁矿或钾铁矿，具体取决于前驱体粉末中氧化镁和二氧化钛的相对化学计量。在更高的温度下，唯一形成的钛酸盐是高达1200℃的硅铝石，而根据原始混合物的化学计量，仅在1300℃以上才会再出现黄铁矿或钾铁矿。当将独立制备的氧化镁和二氧化钛的纳米前体混合在一起并加热到低至400摄氏度至高至600摄氏度的温度时，尽管混合物的化学计量比，仅形成了钾铝石。当纳米颗粒彼此聚结形成钛酸镁时，会发生表面积变化的估算，这表明即使产品保持纳米尺寸，表面能也会发生显着降低。这种减少取决于反应氧化物的绝对和相对粒度以及最终产物的化学计量。讨论了扩散过程，表面能和失配体积对由氧化物形成各种钛酸镁的贡献。由纳米前驱体合成的所有三种钛酸镁在很宽的频率范围内均显示出稳定的介电常数ε，这与用于制造微冷凝器的同等商业粉末相反。此外，由纳米前体合成的原钛酸镁（geikielite）的品质因数Q比市售产品的品质因数Q高约一个数量级。

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