Superconductivity and Jahn-Teller Polarons in Titanates

The present work focuses on the superconductivity phenomenon in La-doped SrTiO3 crystal, and the Jahn-Teller (JT) polarons in BaTiO3 crystal. In the case of SrTiO3 crystal this study shows the occurrence of free electrons in the conduction band of the crystal and explains a number of the experimental results obtained for the superconducting La-doped SrTiO3 existing under 0.3K. Free electrons are found to be situated within the Ti-O planes similar as in the case of the high temperature superconducting (HTS) cuprates. Results obtained for the JT polarons in BaTiO3 crystal explain a number of experimental observations and coincide with the other results obtained independently by the polaron theory. A phenomenological model explaining a bipolaron formation in titanates is suggested and analysed in the present work.