Abstract
We study the incipient ferroelectricity in strontium titanate (ST) by focusing on the Ti-sublattice, which is considered to carry the polar degrees of freedom. The O variables are eliminated to obtain an effective model for the Ti atoms, which are further subjected to an on-site double-well potential. The dielectric constant is calculated exactly on the mean-field level. Good agreement with experiment is achieved with only two parameters as inputs. Moreover, the inputs are tightly constrained by physical reasons. Our study sheds light on the transition-like behaviors that were observed in ST [K.A. Müller, H. Burkard, Phys. Rev. B 19 (1979) 3593]. According to the present analysis, such behaviors are argued to follow from the hopping between high energy intra-well states, and hence intrinsic to the double-well model.
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