Recently, it has been shown that, upon cooling, disordered Pb(Sc1/2Ta1/2)O3 ceramics transform spontaneously from a relaxor state to a ferroelectric state when processed in a manner that suppresses lead vacancies. If lead vacancies are present, the spontaneous ferroelectric transition is suppressed and the ceramics exhibit the usual relaxor behavior in a wide temperature range. It is shown that disordered Pb(Sc1/2Nb1/2)O3 ceramics have a similar nature: When produced in a manner that does not eliminate lead vacancies, they exhibit normal relaxor behavior. However, if stoichiometry is tightly controlled, disordered Pb(Sc1/2Nb1/2)O3 transforms spontaneously (under zero-bias field) from a relaxor into a normal ferroelectric upon cooling.

A zero-field spontaneous relaxor-ferroelectric transition is reported in Pb(Sc0.5Ta0.5)O3 (PST). This behavior is different from that of other relaxors, where such transitions occur only under the field. A highly disordered PST that has the wide relaxation spectrum typical of relaxors is shown to transform spontaneously into a macroscopic ferroelectric state. Introduction of defects (lead vacancies) into the material impedes the transition resulting in the usual relaxor behavior. Dielectric properties of PST, with and without defects, are analyzed. For the interpretation of the observed properties, a model invoking an additional nonpolar phase is proposed. This model does not imply a freezing in the system. At the low-frequency limit, it is possible to account for the Vögel–Fulcher (VF) law for the temperature of the maximum of the dielectric constant, using only the commonly accepted assumption of an exponentially wide relaxation time spectrum that shrinks on heating. The presented approach interprets the observed proximity between the ferroelectric phase transition temperature and that of the freezing temperature obtained from the VF relation.

The wafer flexure technique was used to characterize the d31 coefficient of a number of sol–gel and radio frequency (rf) sputtered lead zirconate titanate (PZT) thin films with thicknesses between 0.6 and 3 μm. Typical d31 values for well-poled 52/48 sol–gel films were found to be between −50 and −60 pC/N. The rf sputtered films possessed large as-deposited polarizations which produced d31 coefficients on the order of −70 pC/N in some unpoled films. The subsequent poling of the material, in a direction parallel to the preferred direction increased the d31 coefficient to values of about −85 pC/N. The aging behavior of the d31 coefficient was also investigated. For sol–gel films the aging rate was found to be independent of poling direction and to range from 4% per decade for a 2.5 μm film to 8% per decade for a 0.6 μm film. In contrast, the aging rate of sputtered films was strongly dependent on poling direction, with maximum and minimum rates of 26% and 2% per decade recorded. These aging rates are very high in light of the limited twin wall motion in PZT films, and are believed to result from the depolarizing effects of internal electric fields in the rf sputtered films and interfacial defects in the sol–gel films.

Complex perovskite A(B′B″)O3 ceramics with various degrees of B-site order have been structurally and spectroscopically characterized by means of x-ray diffraction, transmission electron microscopy, and infrared reflectivity. In Ba(Fe1/2Nb1/2)O3 and Pb(Fe1/2Nb1/2)O3, no order could be detected whereas Pb(In1/2Nb1/2)O3, Pb(Mg1/3Nb2/3)O3, and Pb(Sc1/2Ta1/2)O3 (unannealed) all exhibited weak reflections associated with small ordered regions Pb(Sc1/2Ta1/2)O3 was also prepared by appropriate heat treatment in the fully ordered form and exhibited strong maxima arising from the ordered superlattice in both electron and x-ray diffraction. The infrared reflectivity (30–4000 cm−1) revealed correlation between the degree of ordering and appearance of the extra mode in the 260–320 cm−1 range assigned to B′–B″ vibrations. Despite an apparently low volume fraction of ‘‘ordered material’’ in ‘‘partially ordered’’ samples of Pb(Sc1/2Ta1/2)O3, the extra mode was observable. It is suggested that infrared spectroscopy is sensitive to short-range ordering down to the nm range which is proposed to exist in between the small regions of order.

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