Stannic rutile tetragonal tin oxide ground state and optical properties studied by local spin density approximation, the greens function and bethe salpeter equation.

Abstract

Tin occurs in two main oxides; stannic oxide (SnO 2) and stannous oxide (SnO). The two oxides depicts the dual valence of tin, with oxidation states of 2+ and 4+. Stannous oxide is less well characterized than SnO2. Its electronic band gap is not accurately known but has been estimated to be somewhere in the range of 2.5–3 eV. Thus stannous oxide exhibits a smaller band gap than stannic oxide, which is largely quoted to be 3.6 eV. There are no single crystals available that would facilitate more detailed studies of stannous oxide. As such not much has been done about this oxide. Stannic oxide is the most abundant form of tin oxide [10] and it has more technological significance in gas sensing applications, photo electronic applications and oxidation catalysts. Furthermore besides its common rutile tetragonal structured SnO2 phase there also exists a slightly more dense orthorhombic high pressure phase. Suito et al. showed that in a pressure–temperature diagram the regions of tetragonal and orthorhombic phases can be separated by a straight line of the equation p (kbar) = 140.0 + 0.022T (°C). Owing to the vast applications of stannic Tin Oxide in the field of transparent conducting metal oxides, this project seeks to establish the structural properties, electronic and optical properties of stannic rutile tetragonal tin oxide using purely theoretical predictions. In this project, the ground properties of SnO2 have been studied using Quantum-ESPRESSO code, while the optical properties have been probed using yambo code. The ground state properties are studying using the Local Spin Density Approximation (LSDA). The band gap of SnO2 is found to be 3.6eV a value that agrees with the theoretical value. The Greens Function and the dynamically screened interaction (GW) and the Bethe Salpeter Equation (BSE) have been used to study the absorption energy and the electron energy loss spectra. By the BSE, the value of the band gap is found to be 3.5eV which is close to the available experimental values showing a variance of -2.78% from the experimental value. The absorption spectra obtained from the BSE calculations show that the maximum light absorbed by SnO2 is in the UV wavelength near 10nm which posses that SnO2 is a good absorber of UV of the electromagnetic spectrum. The following SnO2 parameters were used in this work: a=b= 4.1485A° and c=2.6620A°[1,3,6] . This was done by computational methods on SnO2 under its normal manifestation.