PbTiO3 Ferroelectric Single Crystals Research Articles

Impact of Thickness and Poling Condition on Dielectric and Piezoelectric Properties of Pb(In0.5Nb0.5)O3–PbTiO3 Ferroelectric Crystals

The alternating current poling (ACP) method has received many attentions for the improvement of the piezoelectricity of ferroelectric crystals through domain engineering with low cost and high efficiency. However, the effects of ACP and sample thickness have never been reported in ferroelectric crystals with high coercive field. Herein, the piezoelectric and dielectric properties of [001]c‐oriented Pb(In0.5Nb0.5)O3–PbTiO3 ferroelectric single crystals with different thicknesses are investigated using ACP. The highest piezoelectric coefficient d 33 (1720 pC N−1) and free permittivity ε T 33/ε 0 (3690) are obtained for ACP samples with the thickness of 2 mm. The domain structure is significantly affected by the thickness and poling method. The 2 mm ACP samples have the more regular domain structure and smaller domain width compared with others. In addition, the decrease in coercive field is beneficial to the enhancement of the piezoelectric performance.

An I-integral method for crack-tip intensity factor variation due to domain switching in ferroelectric single-crystals

In the present study, an I-integral method is established for solving the crack-tip intensity factors of ferroelectric single-crystals. The I-integral combined with the phase field model is successfully used to investigate crack-tip intensity factor variations due to domain switching in ferroelectricity subjected to electromechanical loadings, which exhibits several advantages over previous methods based on small-scale switching. First, the shape of the switching zone around a crack tip is predicted by the time-dependent Ginzburg–Landau equation, which does not require preset energy-based switching criterion. Second, the I-integral can directly solve the crack-tip intensity factors and decouple the crack-tip intensity factors of different modes based on superimposing an auxiliary state onto an actual state. Third, the I-integral is area-independent, namely, the I-integral is not affected by the integral area size, the polarization distributions, or domain walls. This makes the I-integral applicable to large-scale domain switching. To this end, the electro-elastic field intensity factors of an impermeable crack in PbTiO3 ferroelectric single crystals are evaluated under electrical, mechanical, and combined loading. The intensity factors obtained by the I-integral agree well with those obtained by the extrapolation technique. From numerical results, the following conclusions can be drawn with respect to fracture behavior of ferroelectrics under large-scale switching. Under displacement controlled mechanical loading, the stress intensity factors (SIFs) decrease monotonically due to the domain switching process, which means a crack tip shielding or effective switching-induced toughening occurs. If an external electric field is applied, the electric displacement intensity factor (EDIF) increases in all cases, i.e., the formed domain patterns enhance the electric crack tip loading. The energy release rate, expressed by the crack-tip J-integral, is reduced by the domain switching in all examples, which underlines the switching-induced-toughening effect. In contrast, under stress controlled load, the SIF evolves due to large-scale switching to a stable value, which is higher than the non-switching initial value, i.e., fracture is promoted in this case.

Large acoustic thermal hysteresis in relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-PbTiO3

The diffuse phase transition in relaxor-based 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 ferroelectric single crystals is studied by observing the large thermal hysteresis over 100 K of the longitudinal acoustic (LA) phonon. By observing this hysteresis in the LA phonon frequency with different temperature-cycles, it is concluded that nonequilibrium states are induced by supercooling. Relaxor ferroelectrics easily go supercooling, because they demonstrate structural hierarchy like glass-forming materials. The inhomogeneous structure disrupts sharp phase transitions, revealing diffuse phase transition on cooling. However, annealing at low temperatures reduces the inhomogeneity markedly. These interpretations are consistent with LA phonon behavior under electric fields, which reduce the inhomogeneity.

Mechanical Confinement: An Effective Way of Tuning Properties of Piezoelectric Crystals

AbstractUsing <001>‐oriented Pb(Mg1/3Nb2/3)O3–PbTiO3 ferroelectric single crystals as a model material, the impact of mechanical confinements on polarization hysteresis, coercive field, and remanent polarization of relaxor‐based piezocrystals is investigated. Comparative studies are made among rhombohedral and tetragonal single crystals, as well as a polycrystalline ceramic, under uniaxial and radial compressive pre‐stresses. The dramatic changes observed are interpreted in terms of the piezoelectric effect and possible phase transitions for rhombohedral crystals, and ferroelastic domain switching and the piezoelectric effect for tetragonal crystals. Under radial compressive stresses, the coercive field for the rhombohedral crystal is observed to increase to 0.67 kV/mm and that for the tetragonal crystal is increased to 0.78 kV/mm. This is a 200% increase relative to the unstressed condition. The results demonstrate a general and effective approach to overcome the drawback of low coercive fields in these relaxor‐based ferroelectric crystals, which could help facilitate widespread implementation of these piezocrystals in engineering devices.

Propagation and Deflection of Electric-Field-Induced Microcracks in 0.69Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-0.31PbTiO<sub>3</sub> Ferroelectric Single Crystals

Propagation and deflection of microcracks driven by electric loading in <001>-oriented 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 ferroelectric single crystals were investigated using an in-situ transmission electron microcopy (TEM) technique. The static observation of the domain pattern revealed the coexistence of sub-micrometer and nano-meter domains. Electric field induced deviation from the main microcrack path and subsequent propagation along the direction almost perpendicular to the electric field were observed directly. A qualitative analyses is given based on the maximum energy release rate criterion.