The influence of lattice disorder produced by Mn and Fe substitution on the dielectric properties of the incipient ferroelectric KTaO3 were investigated. Both substituents produce dipolar centers that exhibit relaxational behavior in the audio frequency range. At a concentration of 0.01at%, i.e., in the very dilute limits, the Mn center was reflected in a dielectric loss peak, but not to a measurable degree in the real part of the dielectric function, but a concentration of 0.3at%Mn produced measurable anomalies. In the case of Fe, a concentration of 0.3at% produced anomalies in the dielectric loss. Hydrostatic pressure had a considerable influence on the static and dynamic properties of these materials. The results were explained in terms of microscopic models for these dipolar centers, and it was shown that all of the properties could be understood in terms of the temperature and pressure dependences of the correlation length for dipolar interactions in the highly polarizable KTaO3 host lattice. A model theory was used to describe the influence of random dipolar fields on the reorientation dynamics. The calculations were found to be in good agreement with the experimental data on the 0.3%Mn, where there were weak dipolar correlations.
Dipolar Centers in Incipient Ferroelectrics - Mn and Fe in KTaO3. E.L.Venturini, G.A.Samara, V.V.Laguta, M.D.Glinchuk, I.V.Kondova: Physical Review B, 2005, 71, 094111 (8pp)