Crystal chemistry of hibonite as indicator for oxygen fugacities during solar nebula condensation

富钙铝包裹体(CAI)提供了太阳系固体中最古老的测量年龄，因此可以提供关于早期太阳系星云的温度和氧逸度条件的基本信息。存在于几个CaI中的矿物Hibonite是太阳星云的主要凝聚物之一，含有大量处于不同氧化还原状态的钛。因此，它是洞察早期太阳系氧逸度的理想候选者。到目前为止进行的实验表明，钛的氧化状态不仅取决于形成辉石时的氧逸度，而且还取决于它的晶体化学。因此，需要在不同的温度和氧逸度下进一步合成不同钛、镁、钒含量的辉石，以获得辉石的氧气压计。阳离子在辉石中的分布将通过单晶结构的细化来获得，而合成辉石的EELS谱将被仔细地分析，以获得关于钛的氧化态及其阳离子分布的信息。我们预计，我们的研究对于限制来自不同类型球粒陨石的陨石硫化物的冷凝和改变的复杂历史是必不可少的，这些历史也将使用相同的技术进行分析。

Calcium-aluminium-rich inclusions (CAIs) yield the oldest measured ages of any solar system solid and as such can give essential information on the temperature and oxygen fugacity conditions of the early solar nebula. The mineral hibonite, present in several CAIs, is one of the primary condensates from the solar nebula and contains significant amounts of Ti in different redox states. It is therefore an ideal candidate for providing insight into the oxygen fugacity of the early solar system. Experiments conducted so far reveal that the oxidation state of Ti does not depend solely on the oxygen fugacity at which hibonite is forming, but also on its crystal-chemistry. Further syntheses of hibonites with different Ti, Mg and V contents at different temperatures and oxygen fugacities are therefore necessary to obtain an oxygen barometer for hibonite. Cation distribution in hibonite will be obtained by single-crystal structural refinements, whereas EELS spectra of synthetic hibonites will be carefully analysed in order to obtain information both on the Ti oxidation state and on its cation distribution. We expect that our study will be essential for constraining the complex history of condensation and alteration of meteoritic hibonites from different types of chondrites which will be also analysed using the same techniques.