Anomalous temperature effect on the Fe3+cubic crystalline field splitting in KTaO3(EPR study)

Electron paramagnetic resonance measurements of the cubic crystalline field splitting parameter of Fe3+ at the Ta site in KTaO3 are reported as a function of temperature, pressure, and Nb doping concentration. The relative dependence of the splitting parameter a on the unit-cell volume was found to be similar in the two incipient ferroelectrics KTaO3 and SrTiO3. The explicit temperature effect, i.e. the derivative delta a/ delta T at constant volume and concentration is negative in KTaO3 (and SrTiO3) whereas it is positive in MgO, a typical inert dielectric oxide. This distinction appears to be related to the driving mechanism of ferroelectricity.