Over Half a Century of Research in Oxides

An attempt will be made to recall some of the highlights of the research in oxides achieved by the author and various collaborators over a period of 58 years. These were the observation of the paramagnetic resonance of transition metal ions of high valency like Fe³⁺, Fe⁴⁺, Fe⁵⁺ and Co⁴⁺ and their photochromic behaviour; then the detection of Mn⁴⁺ in BaTiO₃ and the proof for the presence of order–disorder character in these ferroelectric transitions, and then the temperature dependence of the rotational order parameter of the structural phase transitions in LaAlO₃ and SrTiO₃. Near the transition, the observation of critical behaviour compatible with renormalisation group theory and the presence of a Potts transition line, a critical end point and a Lifshitz point under uniaxial stress in SrTiO₃ and CaGdF₃. This will be followed by the determination of the stabilisation energy of the Jahn–Teller effect with octahedral oxygen neighbours to various ions; leading over to the concept of Jahn–Teller polarons as quasi particles for the generation of superconductivity, and the experimental observation of Jahn–Teller bipolarons and their stabilisation energy determined in one of the HTS copper oxides.

A comprehensive collection of relevant papers appeared in the book “Properties of Perovskites and Other Oxides” by K.A. M¨uller and T.W. Kool (World Scientific, 2010).