Band Structure Of SrTiO3 Research Articles

Defect-induced Sr1−xPrxTiO3 crystallites by burial sintering and its optoelectronic applications

The band structure of SrTiO3 was altered by introducing Pr3+ in the Sr2+ site and subsequent graphite burial sintering. The asymmetric nature of the (310) peak in XRD and the emergence of Eg and B1g modes in the Raman spectrum suggest the transformation from cubic to tetragonal phase for the Sr1-xPrxTiO3 system with x ≥ 0.1. The development of the forbidden first-order Raman peaks and novel spectral properties are attributed to the local vibrational modes linked to oxygen vacancies. Structural variations in terms of lattice strain were investigated using a W–H plot, and morphological changes were analyzed by high-resolution FE-SEM. High infrared absorption in UV–Vis–NIR spectra and a significant reduction in band gap from 2.8 eV to 1.8 eV were accomplished through increased disorder in the lattice and the reduction of Ti4+. The blue shift in absorption spectra with Pr concentration can be used to tune the absorption range for sensing purposes. The formation of new electronic states observed here offers a novel approach for band gap modification in perovskites for photocatalytic and photovoltaic applications.

The electronic structure of transition-metal impurities in SrTiO3

The electronic structure of transition-metal impurities is studied using a semi-empirical tight-binding parametrisation of the band structure of SrTiO3, together with the Green function method. The energy levels, with spin polarisation, are calculated for isolated chromium, manganese and cobalt, following previous work on iron and vanadium, together with their associated complex with an oxygen vacancy VO. For charge-transfer processes from valence band, the optical transition spectral shape is deduced and compared with experiments.

A tight-binding model of energy levels of vanadium and iron in SrTiO3

Using a tight-binding parametrisation of the band structure of SrTiO3 together with the Green function method, the authors have calculated the energy levels of vanadium and iron, including spin polarisation. The shape of the optical V5+ and Fe5+ spectra is deduced for charge-transfer processes. The results are compared with experiments. Comparison with recent EPR results for V2+ is also given.

A tight-binding study of energy levels of substitutional transition-metal atoms in SrTiO3

Using a tight-binding parametrisation of the band structure of SrTiO3 together with the Green function method, the authors calculate the energy levels of Cr, Mn, Co and Ni, as was done for iron in a recent paper, with spin polarisation. The shape of optical transition-metal spectra is deduced for charge-transfer processes, and energy values calculated for some observed forbidden d-d transitions. These results are compared with experimental results. A comparison is also given with a previous Xalpha calculation on Co. They discuss the localisation of the occupied impurity levels.

A tight-binding model of the oxygen-vacancy in SrTiO3

Using a tight-binding parameterisation of the band structure of SrTiO3 together with the Green functions method, the authors calculate the energy levels of the oxygen vacancy. They show the ionic character of this defect and compare their results with previous calculation and experiments. They suggest an instability of the neutral and singly ionised vacancy with respect to polaron formation.

Vacuum ultraviolet reflectivity and band structure of SrTiO3 and BaTiO3

The room temperature near-normal incidence reflectance spectra for SrTiO3 and BaTiO3 have been measured in the energy region 10 to 32 eV. The optical constants for the region 0 to 32eV have been derived from a Kramers-Kronig analysis by including earlier measurements for the low energy region. For SrTiO3 five peaks in the Ti3d derived conduction band density of states have been found on the basis of experimental data only, neglecting excitonic effects. The energies of these peaks are in excellent agreement with peaks in the density of states calculated by Mattheiss. The results for BaTiO3 could not be interpreted as unambiguously in such a scheme. Alternatively, some of the transitions could be interpreted as being due to core level excitons.