Krasnov Aleksei G, Koroleva Mariia S, Vlasov Maxim I, Shein Igor R, Piir Irina V, Kellerman Dina G
Institute of Chemistry, Komi Science Center , Ural Branch, Russian Academy of Science , Syktyvkar , Russia.
NANOTECH Center , Ural Federal University , Ekaterinburg , Russia.
Inorg Chem. 2019 Aug 5;58(15):9904-9915. doi: 10.1021/acs.inorgchem.9b01057. Epub 2019 Jul 11.
Combined ab initio and experimental study of Cr doping into bismuth titanate pyrochlore was carried out for the first time. Accurate first-principles density functional theory calculations were performed considering a Hubbard correction (DFT+U) to account for on-site Coulomb interactions of the Cr 3d states. The possibility to synthesize a novel pyrochlore-type compound with a high dopant content BiCrTiO (Bi site doping) in a fine powder state was shown via coprecipitation method, while the single-phase BiTiCrO (Ti site doping) could not be obtained. Detailed descriptions of thermostability, structural, optoelectronic, and magnetic properties of Cr-doped pyrochlores in the fine (particles size 100-300 nm) and "bulk" (1-50 μm) powder states are presented based on the well-matched results of theoretical and experimental investigations. According to the Rietveld refinement of the X-ray diffraction data, BiCrTiO compound is an A-site deficient pyrochlore (BiCr)(TiCr)O with chromium distribution between both cationic sites. Metastability of fine powder Cr-containing pyrochlore phase was revealed during long-thermal annealing, while the bulk powder sample was stable up to its melting point 1230 °C. According to the study of electronic structure and optical properties, Cr-doped pyrochlores are wide-band semiconductors with light absorption in the range of 300-500 nm and perspective as photocatalytic active materials under visible light irradiation. Paramagnetic behavior with effective magnetic moment 3.92 μB (BiCrTiO) and 3.01 μB (BiCrTiO) was experimentally observed. All chromium in magnetically diluted pyrochlore BiCrTiO exists in the form of Cr monomers, whereas in the more concentrated magnetic BiCrTiO composition Cr-O-Cr dimers may also be present, with a fraction equal to 0.39. This investigation constitutes the first approach to the electronic, structural, optical, and magnetic properties of d-elements doped bismuth titanate pyrochlores from experimental and theoretical viewpoints, emphasizing the power of DFT+U to provide insights and to complement the experimental characterization of these new compounds.
首次对铬掺杂钛酸铋烧绿石进行了从头算和实验相结合的研究。考虑到哈伯德修正（DFT+U）以解释Cr 3d态的局域库仑相互作用，进行了精确的第一性原理密度泛函理论计算。通过共沉淀法展示了在细粉状态下合成具有高掺杂含量BiCrTiO（Bi位掺杂）的新型烧绿石型化合物的可能性，而单相BiTiCrO（Ti位掺杂）无法获得。基于理论和实验研究的良好匹配结果，详细描述了细粉（粒径100 - 300 nm）和“块状”（1 - 50 μm）粉末状态下Cr掺杂烧绿石的热稳定性、结构、光电和磁性特性。根据X射线衍射数据的Rietveld精修，BiCrTiO化合物是一种A位缺陷的烧绿石（BiCr）（TiCr）O，铬分布在两个阳离子位点之间。在长时间热退火过程中揭示了含铬细粉烧绿石相的亚稳定性，而块状粉末样品在高达其熔点1230°C时是稳定的。根据电子结构和光学性质的研究，Cr掺杂烧绿石是宽带半导体，在300 - 500 nm范围内有光吸收，有望成为可见光照射下的光催化活性材料。实验观察到有效磁矩为3.92 μB（BiCrTiO）和3.01 μB（BiCrTiO）的顺磁行为。在磁性稀释的烧绿石BiCrTiO中，所有铬都以Cr单体的形式存在，而在浓度更高的磁性BiCrTiO组合物中，也可能存在Cr - O - Cr二聚体，其比例等于0.39。本研究从实验和理论角度首次探讨了d元素掺杂钛酸铋烧绿石的电子、结构、光学和磁性特性，强调了DFT+U在提供见解和补充这些新化合物实验表征方面的作用。
