On the relationship between ionic displacement and the curie temperature and spontaneous polarization in displacive ferroelectrics

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Abstract
It is suggested that measurements of the pressure dependence of the Curie temperature (Tc) and of the spontaneous polarization (Ps) are very useful in examining the relationships suggested by Abrahams, et al., for displacive ferroelectrics. These are relationships between Tc or Ps and the relative displacement (Az) developed by the homopolar metal ion (e.g. Ti in BaTiO3) along the polar axis. The necessary experimental data are available on BaTiO3, PbTiO3 and SbSI. The results show that the coefficient x appearing in the Tc(Δz) expression is not a true constant but increases substantially with increasing pressure. This increase is to be expected if x is qualitatively interpreted as an average force constant between the homopolar ion and the surrounding ions. The lattice dynamical implications of the results are discussed briefly.