Particle-size effect on the ferroelectric phase transition in PbSc1/2Ta1/2O3 ceramics

Abstract

The particle-size dependence on the ferroelectric phase transition in nanocrystalline PbSc1/2Ta1/2O3 ceramics has been investigated for particles in the 0.01–0.16 μm size range. The phase transition was monitored through measurement of the dielectric constant as a function of temperature, variable temperature x-ray diffraction, and differential scanning calorimetry. The c/a tetragonality ratio decreased monotonically with particle size, reducing to unity at 0 °C for particles ⩽0.053 μm in size. The ferroelectric transition temperature Tc decreased gradually and the phase transition became more diffuse in nature as the particle size decreased. Below a mean particle size of 0.02 μm there was no peak in either the dielectric constant or the differential scanning calorimetry curve as a function of temperature, even though variable temperature x-ray diffraction could detect tetragonality indicative of ferroelectric distortions at sufficiently low temperatures down to the smallest crystallite size of 0.01 μm.

Electrical Properties of Nb-Doped PZT 65/35 Ceramics: Influence of Nb and Excess PbO

“…From a microscopic level, this behavior should be accounted for by the fact of dealing with ferroelectric micro-regions embedded in a nonferroelectric (porous) medium, allowing to a defectassociated lost of the (i) overall material polar coupling and (ii) apparent local composition homogeneity. We should however point out that, as compared to strong or nearly-strong relaxor diffuse ferroelectric materials [6,22,25,28], these PZTN samples indeed show only a 'partial' rather than a properly or great diffuseness character of phase transition, with relatively poor dielectric peaks broadness (see e.g. Figs.…”

“…The value of the Curie-Weiss temperature resulted in T o = 372 • C, while that of the transition is T m = 354 • C. Deviation from the Curie-Weiss law is a typical characteristic of ferroelectric materials exhibiting a Diffuse Phase Transition (DPT), in the sense that their ε versus T spectra involve broad rather than sharp dielectric peaks. In the literature, the appearance of diffuseness has been normally argued in terms of variations in local composition giving rise to distinct microregions, each of which has a slightly different Curie point for its ferro-paraelectric phase transition [21,22,25,26]. A so-called Curie region over which develops a broad rather than sharp dielectric peak must be thus considered.…”

“…In such cases, the phase transition may be considered as "no purely" diffuse, in contrast to the "pure" DPT described by the Smolenskii-Isupov relation. The characteristics of DPT in ferroelectric materials have proved, in general, to correspond to variable exponents in the range 1 < γ ≤ 2 [22,25,26]. From the electrical data interpretation point of view, the characteristics of the phase transition of any ferroelectric material can be argued in terms of a generalized empirical equation of the type:…”

“…A so-called Curie region over which develops a broad rather than sharp dielectric peak must be thus considered. According to Smolenskii and Isupov, the DPT should be described by the quadratic relation [21,22,25]:…”

“…The above results indeed involve the effect of correction to the true material permittivity from contribution of porosity as well as segregation of free PbO phase as in the case of y = 25. Such an analysis procedure has been widely considered in the literature [18][19][20][21][22]. Porosity and lead oxide are two phases with lower permittivities than ferroelectric grains.…”