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首页> 外文期刊>Acta Crystallographica, Section B. Structural science, crystal engineering and materials >High-temperature Fe oxidation coupled with redistribution of framework cations in lobanovite, K2Na(Fe~(2+)_4Mg_2Na)Ti_2(Si_4O_(12))_2O_2(OH)_4 - the first titanosilicate case
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High-temperature Fe oxidation coupled with redistribution of framework cations in lobanovite, K2Na(Fe~(2+)_4Mg_2Na)Ti_2(Si_4O_(12))_2O_2(OH)_4 - the first titanosilicate case

机译：高温Fe氧化与叶片岩中骨架阳离子的再分布，K2NA（Fe〜（2 +）_ 4mg_2NA）Ti_2（Si_4O_（12））_ 2O_2（OH）_4 - 第一个钛硅酸盐案例

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摘要

The high-temperature (HT) behaviour of lobanovite, K_2Na(Fe~(2+)_4Mg_2Na)Ti_2-(Si_4O_(12))_2O_2(OH)_4, was studied using in situ powder X-ray diffraction in the temperature range 25-1000°C and ex situ single-crystal X-ray diffraction of 17 crystals quenched from different temperatures. HT iron oxidation associated with dehydroxylation starts at 450°C, similar to other ferrous-hydroxy-rich heterophyllosilicates such as astrophyllite and bafertisite. A prominent feature of lobanovite HT crystal chemistry is the redistribution of Fe and Mg+Mn cations over the M(2), M(3), M(4) sites of the octahedral (O) layer that accompanies iron oxidation and dehydroxylation. This HT redistribution of cations has not been observed in titanosilicates until now, and seems to be triggered by the need to maintain bond strengths at the apical oxygen atom of the TiO_5 pyramid in the heteropolyhedral (H) layer during oxidation- dehydroxylation. Comparison of the HT behaviour of lobanovite with fivecoordinated Ti and astrophyllite with six-coordinated Ti shows that the geometry of the Ti polyhedron plays a key role in the HT behaviour of heterophyllosilicates. The thermal expansion, geometrical changes and redistribution of site occupancies which occur in lobanovite under increasing temperature are reported. A brief discussion is given of minerals in which the cation ordering (usually for Fe and Mg) occurs together with iron oxidation- dehydroxylation at elevated temperatures: micas, amphiboles and tourmalines. Now this list is expanded by the inclusion of titanosilicate minerals.
机译：使用在温度范围内的原位粉末X射线衍射研究，研究了洛尾岩，K_2NA（Fe〜（2 +）（Fe〜（2 +）_ 4Mg_2NA）Ti_2-（Si_4O_（OH））_ 2O_2（OH）_4的高温（HT）行为。 -1000°C和Ex原位单晶X射线衍射从不同的温度淬火。与脱羟基化相关的HT铁氧化在450℃下开始，类似于其他富含羟基的富含氟硅酸盐，例如天空管和Bafertisite。洛盆岩HT晶体化学的突出特征是伴随铁氧化和脱羟基化的八面体（O）层的M（2），M（3），M（4）位点上的Fe和Mg + Mn阳离子的再分布。迄今为止，该HT的阳离子尚未观察到阳离子的再分布，似乎是由于在氧化 - 脱羟基化期间在杂多亚葡萄球菌（H）层中的TiO_5金字塔的顶端氧原子处的粘合强度需要触发。六叶片与六协调Ti的叶片叶片HT行为的比较表明，Ti Polyhedron的几何形状在杂草碱的HT行为中起着关键作用。报道了在增加温度下，洛尾岩中出现的场地占用的热膨胀，几何变化和再分配。还给出了矿物质的矿物质，其中阳离子排序（通常用于Fe和Mg）与升高的温度下的铁氧化 - 脱羟基化一起发生：云母，两噬菌体和林林碱。现在该列表通过包含钛硅酸盐矿物而扩大。

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