Modelling of substitutional defects in the structure of Ti-bearing hibonite

• Published in: Journal of structural chemistry 2016-12, Vol.57 (7), p.1369-1376
• Main Authors: Pankin, I. A., Kravtsova, A. N., Polozhentsev, O. E., Soldatov, A. V.
• Format: Article
• Language: English
• Subjects: Absorption; Aluminum; Applications of Synchrotron Radiation in Structural Chemistry; Atomic; Atomic structure; Atomic/Molecular Structure and Spectra; Bearing; Chemistry; Chemistry and Materials Science; Defects; Inorganic Chemistry; Mathematical models; Molecular; Optical and Plasma Physics; Physical Chemistry; Solid State Physics; Spectra; Titanium; X-rays
• ISSN: 0022-4766; 1573-8779
• DOI: 10.1134/S0022476616070106

A local atomic structure around titanium positions in Ti-bearing hibonite (CaAl 12 O 19 ) has been studied. The structural models of substitution of different substitution defects Ti–Al in hibonite by titanium atoms have been considered. Optimization of structural models of hibonite has been done by means of density functional theory calculations using pseudopotential approximation as implemented in VASP 5.3 code. Gibbs free energies analysis has shown that models of substitution of M2 and M4 aluminum positions by titanium atoms are the most probable. For the most probable structural models of Ti-bearing hibonite theoretical X-ray absorption near-edge structure (XANES) spectra near the titanium K edge have been calculated. Significant differences in theoretical XANES spectra calculated for different structural models with non-optimized and optimized atomic structure have been demonstrated. Changes in the intensity of pre-edge structure of Ti K XANES spectra for different substitution models of aluminum by titanium have been observed which relate to different titanium coordination in structural models. Energy shift of spectral features towards lower energy for optimized models implies increase of interatomic distances in local surroundings of Ti absorbing atoms.