Role of Defects in the Ferroelectric Relaxer Lead Scandium Tantalate

Unlike Pb(Mg1/3Nb2/3)O-3 and similar ferroelectric relaxors which never truly become ferroelectric at zero-field, disordered Pb(Sc1/2Ta1/2)O-3 (PST) is a relaxer that spontaneously transforms into a ferroelectric phase. The control of the degree of order of the B-site cations in PST by appropriate heat treatment has been often used to demonstrate the influence of chemical disorder on the dielectric properties of ferroelectrics. Here it is shown that, in PST, disorder itself is not sufficient to prevent a macroscopic ferroelectric transition, and that disordered stoichiometric PST exhibits a strong dielectric relaxation, but upon cooling it spontaneously becomes a macroscopic ferroelectric. Lead deficiency in disordered Pb(Sc1/2Ta1/2)O-3 prevents this spontaneous ferroelectric transformation, and the material shows more usual relaxer properties.