Density Functional Theory Driven Analysis of the Interplay among Structure, Composition, and Oxidation State of Titanium in Hibonite, Spinel, and Perovskite,ACS Earth and Space Chemistry

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Density Functional Theory Driven Analysis of the Interplay among Structure, Composition, and Oxidation State of Titanium in Hibonite, Spinel, and Perovskite
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2021-02-18 , DOI: 10.1021/acsearthspacechem.0c00309
Abu Asaduzzaman ₁ , Krishna Muralidharan _{2,

3} , Thomas J. Zega _{2,

3}

Affiliation

Hibonite (CaAl₁₂O₁₉), spinel (MgAl₂O₄), and perovskite (CaTiO₃) represent oxides that occur in primitive meteorites and are among some of the first phases to have condensed from the early solar nebula. Hibonite and spinel can contain 3d transition metals such as titanium that substitute at cation sites. The substituted titanium can occur in multiple oxidation states, which are in turn linked to the redox conditions under which the material formed or last equilibrated. Similarly, in perovskite, the oxidation state of titanium can also vary but depends on the extent of nonstoichiometry that can arise because of the presence of oxygen vacancies. Here we present density functional theory-based calculations that provide a fundamental understanding on the interplay among changes in composition, structure, and the oxidation state of titanium in spinel, perovskite, and hibonite, with an added emphasis on characterizing the underlying role of oxygen vacancies. Single-site substitution by titanium for aluminum and coupled substitution in conjunction with divalent cations such as magnesium were examined for hibonite and spinel. In addition, the crystal-chemical effects of a single oxygen vacancy were examined in all three systems. Our results show that in hibonite, the M2 cation site is preferred for single titanium substitution, where the titanium oxidation state corresponds to 3+. For the coupled substitution system, the M4 and M3 sites are energetically favorable for titanium and magnesium, respectively, with the oxidation state of titanium corresponding to 4+. In the case of spinel, the substitution of titanium in any of the octahedral aluminum sites are equivalent, and interestingly, substituted titanium is more reduced in spinel as compared with hibonite for both single as well as coupled substitution cases. Further, the oxidation state and Ti–O bonding of couple-substituted titanium in spinel is similar to the titanium cations in the phase-pure perovskite structure. For hibonite and spinel with an oxygen vacancy, we restricted our examination to mono- and di-coupled substitution with the choice motivated by available experimental data. Our results suggest that the oxidation state and the chemical bonding of the substituted titanium cations is directly influenced by their spatial location with respect to the oxygen vacancy.

中文翻译：

密度泛函理论驱动的钛在钛矿，尖晶石和钙钛矿中钛的结构，组成和氧化态之间相互作用的分析

菱铁矿（CaAl ₁₂ O ₁₉），尖晶石（MgAl ₂ O ₄）和钙钛矿（CaTiO ₃）代表了发生在原始陨石中的氧化物，并且属于早期太阳星云中凝结的第一个阶段。菱铁矿和尖晶石可以包含3 d过渡金属，例如钛，可在阳离子位置取代。取代的钛可以多种氧化态出现，这些氧化态又与形成或最后平衡材料的氧化还原条件有关。类似地，在钙钛矿中，钛的氧化态也可以变化，但是取决于由于氧空位的存在而引起的非化学计量的程度。在这里，我们介绍了基于密度泛函理论的计算方法，这些计算方法提供了有关尖晶石，钙钛矿和钙钛矿中钛的成分，结构变化和氧化态之间相互作用的基本理解，并着重强调了氧空位的潜在作用。对钛进行单点取代以取代铝，并结合二价阳离子（如镁）进行偶合取代，以鉴定其是否为菱沸石和尖晶石。另外，在所有三个系统中检查了单个氧空位的晶体化学作用。我们的结果表明，在菱铁矿中，M2阳离子位点是单个钛取代的首选，其中钛的氧化态对应于3+。对于偶合取代系统，M4和M3位分别对钛和镁在能量上有利，而钛的氧化态对应于4+。就尖晶石而言，在任何八面体铝位点中钛的取代都是等效的，有趣的是，在单晶和偶合替代情况下，尖晶石的取代钛都比hibonite减少更多。此外，尖晶石中偶合取代的钛的氧化态和Ti–O键类似于纯相钙钛矿结构中的钛阳离子。对于具有氧空位的菱锰矿和尖晶石，我们根据现有实验数据的选择将检查范围限制为单偶联和双偶联取代。我们的结果表明，取代态钛阳离子的氧化态和化学键直接受其相对于氧空位的空间位置的影响。对于具有氧空位的菱锰矿和尖晶石，我们根据现有实验数据的选择将检查范围限制为单偶联和双偶联取代。我们的结果表明，取代态钛阳离子的氧化态和化学键直接受其相对于氧空位的空间位置的影响。对于具有氧空位的菱锰矿和尖晶石，我们根据现有实验数据的选择将检查范围限制为单偶联和双偶联取代。我们的结果表明，取代态钛阳离子的氧化态和化学键直接受其相对于氧空位的空间位置的影响。

更新日期：2021-03-18

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