Effects of quenched disorder on La-modified lead zirconate titanate: Long- and short-range ordered structurally incommensurate phases, and glassy polar clusters

Abstract

Structure–property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio by transmission electron microscopy, lattice imaging, and dielectric spectroscopy. Investigations were performed for 65/35⩽Zr/Ti⩽90/10. These investigations have demonstrated a general trend in domain structure and polar order with increasing quenched impurity concentration. For Zr/Ti ratios of 90/10 and 85/15, a structurally incommensurate antiferroelectric (AFEin) state was found to be stabilized with increasing La. Temperature dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (λ) was found to increase significantly with increasing Ti. When λ increased to ∼40 Å, polar clusters began to condense from the AFEin order. For Zr/Ti ratios of 80/20 and 65/35, increasing quenched disorder was found to result in the evolution of polar order through a common sequence of domainlike states including polar clusters, tweedlike structures, and normal micron-sized polydomain structures. These results, in conjunction with dielectric spectroscopy, demonstrate a crossover between a long-period incommensurately modulated state and a relaxor ferroelectric state with increasing quenched disorder. Clearly, both quenched disorder (i.e., random fields) and competing polar orderings (i.e., frustration) underlay the unique behaviors of PLZT.

In situ transmission electron microscopy study of the electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic

“…6,7 The hot-stage in situ TEM observations revealed that the modulation wavelength increases continuously with increasing temperature. Based on these studies, Viehland et al 8 suggested that the competing ferroelectric and antiferroelectric ordering in these perovskites are responsible for the presence of incommensurate modulations. However, unambiguous evidence has yet to be found.…”

“…In the PLZT system, the modulation wavelength was observed to increase with Ti molar fraction. 8 Utilizing temperature as the controlled variable in the study of such transformations allows in situ TEM studies, where the evolution of the satellite reflections can be directly observed. 6,7 The hot-stage in situ TEM observations revealed that the modulation wavelength increases continuously with increasing temperature.…”

“…20 It has been suggested that in PZT-based ferroelectric perovskites, the presence of incommensurate modulations in the antiferroelectric phase is a result of the competition between the ferroelectric and antiferroelectric ordering. 8 The continuous increase in the modulation wavelength with increasing temperature is interpreted that there exists a ferroelectric phase within a narrow temperature range just below the paraelectric transition temperature. When temperature is raised close to this temperature range the ferroelectric ordering is enhanced.…”

“…The wave vector is parallel to the ͗110͘ direction in most cases and the wavelength lies in the range of 5 ϳ 20a, where a is the lattice parameter for the parent paraelectric structure. 8 Transformation of the intermediate incommensurate phase to other phases can be triggered by external stimuli, such as chemical composition and temperature. [6][7][8][9][10] Sn-or Ti-content in the PZST system and La content in the PLZT system were utilized before as controlling variables for the phase transformation.…”

“…[6][7][8][9][10] Sn-or Ti-content in the PZST system and La content in the PLZT system were utilized before as controlling variables for the phase transformation. [8][9][10] In the PZST system, it has been shown that decrease in Sn content or increase in Ti content leads to the incommensurate antiferroelectric-to-ferroelectric phase transformation. In the PLZT system, the modulation wavelength was observed to increase with Ti molar fraction.…”