Intrinsic defects in silicate crystals: numerical calculations in the case of diopside

• Grant number: 07/08008-0
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: June 01, 2008
• End date: May 31, 2011
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Shigueo Watanabe
• Grantee: Nilo Francisco Cano Mamani
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

In our laboratory, an extended Project is in progress, with a purpose to investigate physical properties of available natural Brazilian minerals of silicate. Such properties are strongly dependent on points defects in the crystal, both intrinsic and extrinsics. The principal and basic molecule in any silicate crystal structure is the tetrahedron SiO4, with oxygen ions occupying vertices and the silicon ion the center of tetrahedron. Obviously, the quartz has also SiO4 and only SiO4 in its crystal structure.The best know intrinsic defects is the oxygen vacancy, from which several others are originated, such as E1, E2, E4, etc., centers. The stability of neutral oxygen vacancy, of E1 center which is an oxygen vacancy that captured one electron has been investigated theoretically by Rudra & Fowler (1987), quite extensively. They used theory of molecular orbital in a program called MINDO/3. Today, it is superseded by another one called CRYSTAL06. In more than 12 natural mineral of silicates investigated in our laboratory. The EPR measurements have always revealed the E1 center. This means that, oxygen vacancy are present inside these minerals. On the other hand, any silicate mineral has in its structure, one or more oxide of cations, other than Si4+, and that means oxygen vacancy and E1, E2, E4 centers should present the effects of other oxides.In the presents work, a theoretical analysis of the effect of the presence of one or more oxide of cations other than SiO4 will carried out using CRYSTAL06. There is one other important defect center. This due to a foreign atom (called impurity), namely aluminum with charge 3+. It is known the fact that the aluminum ion usually substitute silicon ion with charge 4+. The detail of the formation mechanism will not be described in this abstract, but the replacement of Si4+ by Al3+ result in a well known aluminum center. This will also be analysed with CRYSTAL06. There are others defects that, eventually will be investigated. (AU)

Scientific publications

(7)

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

CANO, NILO F.; AYTA, WALTER E. F.; WATANABE, SHIGUEO. Electronic and optical properties of grossular garnet (Ca3Al2Si3O12): An ab initio study. Optical Materials, v. 32, n. 5, p. 566-569, MAR 2010. (07/08008-0)

CANO, NILO F.; AYTA, WALTER E. F.; WATANABE, SHIGUEO. The electronic and optical properties of sodalite (Na8Al6Si6O24Cl2) from first principles. Solid State Communications, v. 150, n. 3-4, p. 195-197, JAN 2010. (07/08008-0)

CANO, NILO F.; WATANABE, SHIGUEO. Ab initio study of the electronic and optical properties of sillimanite (Al2SiO5) crystal. Optical Materials, v. 33, n. 11, p. 1813-1816, SEP 2011. (07/08008-0)

CANO, NILO F.; BLAK, ANA R.; WATANABE, SHIGUEO. Electron paramagnetic resonance and the thermoluminescence emission mechanism of the 280 degrees C peak in natural andalusite crystal. Journal of Luminescence, v. 131, n. 7, p. 1545-1549, JUL 2011. (07/08008-0)

CANO, NILO F.; BLAK, ANA R.; AYALA-ARENAS, JORGE S.; WATANABE, SHIGUEO. Mechanisms of TL for production of the 230 degrees C peak in natural sodalite. Journal of Luminescence, v. 131, n. 2, p. 165-168, FEB 2011. (07/08008-0)

CANO, NILO F.; WATANABE, SHIGUEO. Theoretical investigation of electronic and optical properties of andalusite within density functional theory. Solid State Communications, v. 150, n. 43-44, p. 2154-2157, NOV 2010. (07/08008-0)

CANO, N. F.; BLAK, A. R.; WATANABE, S.. Correlation between electron paramagnetic resonance and thermoluminescence in natural sodalite. PHYSICS AND CHEMISTRY OF MINERALS, v. 37, n. 1, p. 57-64, JAN 2010. (07/08008-0)