Инд. авторы:	Pan Y., Mashkovtsev R.I., Huang D., Mao M., Shatskiy A.
Заглавие:	Mechanisms of Cr and H incorporation in stishovite determined by single-crystal EPR spectroscopy and DFT calculations
Библ. ссылка:	Pan Y., Mashkovtsev R.I., Huang D., Mao M., Shatskiy A. Mechanisms of Cr and H incorporation in stishovite determined by single-crystal EPR spectroscopy and DFT calculations // American Mineralogist. - 2011. - Vol.96. - Iss. 8-9. - P.1331-1342. - ISSN 0003-004X. - EISSN 1945-3027.
Внешние системы:	DOI: 10.2138/am.2011.3762; SCOPUS: 2-s2.0-80053278036;
Реферат:	eng: Synthetic stishovite before and after electron- and γ-ray irradiation has been investigated by single-crystal electron paramagnetic resonance (EPR) spectroscopy for the first time. Room-temperature single-crystal EPR spectra of as-is stishovite reveal two high-spin (S = 3/2) Cr3+ centers: one with D2h symmetry and another of triclinic symmetry. Quantitatively determined spin Hamiltonian parameters, including matrices g, D, and A( 53Cr) and high-spin Zeeman term BS3, suggest that the D2h center represents a substitutional Cr3+ ion at the Si site without an immediate charge compensator. The triclinic center, which is characterized by a well-resolved 1H superhyperfine structure, also arises from a substitutional Cr3+ ion at the Si site but has an H+ charge compensator bonded to one of the four equatorial oxygen atoms. The magnitude and orientation of the 1H superhyperfine structure yield the location of the H atom at (0.46, 0.12, 0). These structural models for Cr and H in stishovite also have been corroborated by periodic density functional theory (DFT) calculations using the Vienna ab initio simulation package (VASP), with 2 × 2 × 4 supercells, plane-wave basis sets and the projector augmented wave (PAW) potentials. In addition, 85 K EPR spectra of irradiated stishovite show that the two Cr3+ centers are both converted to an S = 1/2 Cr5+ center characterized by two 29Si superhyperfine structures arising from interactions with two nearest and eight second-nearest Si atoms, respectively. The spin Hamiltonian parameters of this Cr5+ center provide further support for the location of the two Cr3+ centers at the Si site.
Ключевые слова:	53Cr hyperfine; Local structure; temperature; stishovite; quantitative analysis; numerical model; irradiation; hydrogen; electron spin resonance; chromium; Substitution mechanism; Stishovite; Site occupancy; Single-crystal EPR; 29Si and 1H superhyperfine; Periodic DFT calculations;
Издано:	2011
Физ. характеристика:	с.1331-1342