Gurlo Aleksander, Kroll Peter, Riedel Ralf
Fachbereich Material- und Geowissenschaften, Technische Universitaet Darmstadt, Petersenstrasse 23, Darmstadt, Germany.
Chemistry. 2008;14(11):3306-10. doi: 10.1002/chem.200701830.
The description of structural relations between bixbyite- and corundum-type structures is of particular interest because of the common occurrence of both structures. One of the representative examples of the bixbyite to corundum transition is the high-pressure high-temperature synthesis of the corundum-type indium oxide. The wet chemistry synthesis and stabilisation of the corundum-type In(2)O(3) under ambient pressure conditions calls for a re-interpretation of the In--O phase diagram as well as for the clarification of the phase transitions in In(2)O(3). One of the questions to be clarified is the stability of the corundum-type In(2)O(3). In the present work we studied the stability of the corundum-type In(2)O(3) both theoretically (by density-functional calculations) and experimentally. The synthesis of the corundum-type In(2)O(3) was performed by the modified non-alkoxide sol-gel method based on the ammonia-induced hydrolysis of indium nitrate in methanol. The corundum-type In(2)O(3) was subjected to thermal analysis (STA) as well as to structural studies, that is, it was examined using X-ray powder diffraction (XRPD) including in situ XRPD characterisation upon thermal treatment. For the first time we have undoubtedly demonstrated, both theoretically and experimentally, the metastability of the corundum-type In(2)O(3) polymorph. The In(2)O(3) polymorph appears to be metastable throughout the entire enthalpy-pressure phase diagram. Upon heating, corundum-type In(2)O(3) transforms irreversibly into cubic bixbyite-type In(2)O(3) as shown by STA as well as in situ heating XRPD experiments. Computations indicate the existence of another high-pressure modification of In(2)O(3) with orthorhombic structure, iso-typic to Rh(2)O(3)-II. We predict this new phase to form at pressures exceeding 15 GPa from both the cubic bixbyite-type and the corundum-type modification of In(2)O(3).
由于方铁锰矿型结构和刚玉型结构都普遍存在，因此对它们之间结构关系的描述格外引人关注。方铁锰矿向刚玉转变的一个典型例子是高温高压合成刚玉型氧化铟。在常压条件下通过湿化学合成法制备并稳定刚玉型In₂O₃，这需要重新解释In - O相图，并阐明In₂O₃中的相变。需要阐明的问题之一是刚玉型In₂O₃的稳定性。在本工作中，我们通过理论计算（密度泛函计算）和实验研究了刚玉型In₂O₃的稳定性。刚玉型In₂O₃是通过改进的非醇盐溶胶 - 凝胶法合成的，该方法基于硝酸铟在甲醇中氨诱导水解。对刚玉型In₂O₃进行了热分析（STA）以及结构研究，即使用X射线粉末衍射（XRPD）进行检测，包括热处理过程中的原位XRPD表征。我们首次在理论和实验上确凿地证明了刚玉型In₂O₃多晶型的亚稳性。在整个焓 - 压相图中，In₂O₃多晶型似乎都是亚稳的。如STA以及原位加热XRPD实验所示，加热时，刚玉型In₂O₃不可逆地转变为立方方铁锰矿型In₂O₃。计算表明存在另一种具有正交结构的In₂O₃高压变体，它与Rh₂O₃ - II同型。我们预测，在压力超过15 GPa时，立方方铁锰矿型和刚玉型In₂O₃变体都会形成这种新相。
