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Rutile structure superlattice first principles calculations

Author: HanJingMei
Tutor: XieWenHui
School: East China Normal University
Course: Condensed Matter Physics
Keywords: first-principle calculation rutile superlattice half-metal
CLC: O469
Type: Master's thesis
Year: 2011
Downloads: 85
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Abstract

In recent years, based on first-principles density functional theory (Frist-principle or ab initio) calculation method has become an important means of scientific research. Especially in the past half-century development and application of high-speed computers, has become a first-principles calculation method of research and development of new materials is an important way. Transition metal oxides its special physical properties, in many areas have important application value. The last century, scientists were on the rutile structure with a transition metal oxide chromium dioxide (CrO2), titanium dioxide (TiO2), vanadium dioxide (VO2), rubidium dioxide (RuO2), iridium dioxide (IrO2 ), zirconia (ZrO2), tin oxide (SnO2), manganese dioxide (MnO2) theoretically and experimentally in depth and meticulous research, and there are many related research reports [1-5]. Such oxides have been widely used in industry. In recent years, as technology continues to improve, Atomic Layer Controlled Growth in the experiment has been achieved by epitaxy. Have the same structure as CrO2, TiO2 and VO2 lattice mismatch of 4%, which means that can be obtained under certain conditions and CrO2/VO2 CrO2/TiO2 heterogeneous superlattice structure. Taking into account the complexity of nanosystems, using first-principles calculation method and explore its nature, is of great significance. In this paper, first-principles calculation method systematically studied the following four conditions: 1, CrO2 lattice constant as the original cell basis vectors along the (001) direction to build the superlattice, the Cr layer superlattices and Ti layer a certain percentage of edge (001) ordered with (CrO2) m / (TiO2) n represents. 2 to CrO2 lattice constant as the original cell basis vectors along the (001) direction to build the superlattice, the Cr layer superlattice layers in a certain proportion and V along (001) direction ordered with (CrO2) m / (VO2) n represents. 3, using TiO2 lattice constant as the original cell basis vectors along the (001) direction to build the superlattice, the Ti layer superlattices and Cr layer along a certain proportion of (001) orientation ordered with (TiO2) m / (CrO2) n represents. 4 to VO2 lattice constant as the original cell basis vectors along the (001) direction of the superlattice build the superlattice layer V and Cr layer along a certain proportion of (001) orientation ordered with (VO2) m / (CrO2) n expressed in this paper we study the m, n = 1,2,3 situation. The calculated results show (CrO2) m / (TiO2) n and (TiO2) m / (CrO2) n After optimization, Ti-O bond length becomes longer, and Cr-O bond length becomes shorter. (CrO2) m / (VO2) n and (VrO2) m / (CrO2) n bond lengths and angles before and after optimization also have change, but change is random. We superlattice (TiO2) m / (CrO2) n and (VO2) m / (CrO2) n do volume optimization, fixed a, b-axis values, changing the size of the c-axis values, found that most superlattice c-axis is no obvious shrinkage and stretching. In addition to (VO2) 2 / (CrO2) 2 superlattices, which have four superlattice ferromagnetic half-metallic nature. Each superlattice 2μB Cr atomic magnetic moment contribution, the magnetic moment of each of Ti atom 0μB, 1μB contribution of each V atomic magnetic moment, this value is not as Cr, Ti, V layer changes the proportion of changed. For (CrO2) m / (TiO2) n and (TiO2) m / (CrO2) n superlattice, the spin-down electron states bandgap bandgap with CrO2 little difference spin down, and when the Ti atomic layer fixed, with the increase of Cr atomic layer, the band gap becomes gradually smaller. For (CrO2) m / (VO2) n and (VO2) m / (CrO2) n superlattice, the spin-down electron states bandgap CrO2 spin down to less than the bandgap. CrO2 comparison unit cell of Cr t2g state role of Ti atom, the superlattice (CrO2) m / (TiO2) n, and (TiO2) m / (CrO2) n t2g Cr in high energy state to the direction of movement, and (CrO2) m / (VO2) n and (VO2) m / (CrO2) n V atoms due to the role of Cr t2g move to the lower energy state.

Rutile structure superlattice first principles calculations

Abstract

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