Nonpolar Axis Research Articles

Domain-engineered Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals: Enhanced piezoelectricity and optimal domain configurations

In this letter, we report a mesoscopic theory of ferroelectrics to explain the dramatically enhanced piezoelectricity in relaxor ferroelectric single crystals poled along a nonpolar axis, where the coexistence of several variants leads to complicated domain configurations. The engineered domain configuration is constructed first using energy minimization approach, and the effective moduli of single crystals with engineered domain configuration are then determined using the lamination theory. Using this approach, we calculate the effective electromechanical moduli of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) crystals poled along [001] and [011] directions, which agree well with experimental observations. In addition, we demonstrate that PMN-PT crystals electromechanically poled by an electric field along [001] direction and an additional positive shear stress σ12 possess superior electromechanical coupling factors k31 and k33 simultaneously, while crystals with other domain configurations demonstrate much lower k31. The analysis reveals that greatly enhanced electromechanical coupling can be obtained in domain-engineered ferroelectric crystals, and offers insight on the design and optimization of ferroelectrics for enhanced functional properties.

Design and ferroelectric properties of polar-axis-oriented polycrystalline Bi4−xPrxTi3O12 thick films on Ir/Si substrates

A route for polar-axis-oriented films with Bi4Ti3O12 (BIT)-type structure was presented. Bi4−xPrxTi3O12 (x=0.0, 0.3, 0.5, 0.7) films were grown on Ir/Si substrates from chemical solutions and formation of IrO2 from Ir layers fostered the nucleation of grains with a and b axes mixed orientation by lattice matching and pseudo-orthogonal c axes was aligned in-plane. Furthermore, by setting the heat treatment temperature for grain growth above the Curie temperature TC, the residual strain between the film and Si introduced lateral stress on cooling and aligned the ferroelectric polar axis separately along the film normal leaving the nonpolar axis in-plane. The polar-axis-oriented film exhibited superb ferroelectric properties with remanent and saturation polarizations of 2Pr=92 and Psat=50 μC/cm2 (x=0.3).

The enhanced and optimal piezoelectric coefficients in single crystalline barium titanate with engineered domain configurations

In this letter, we report a micromechanical analysis to explain the enhanced piezoelectric coefficients in ferroelectric single crystals poled along a nonpolar axis, where the coexistence of several variants leads to a complicated domain configuration. The engineered domain configuration in the crystal is constructed first using energy minimization approach, and the effective moduli of single crystal with engineered domain configuration is then determined using homogenization theory. Following this procedure, we calculate the effective electromechanical moduli of tetragonal barium titanate poled along [111] direction, where the piezoelectric coefficient d33 is found to be 70% higher than those poled along [001], consistent with experimental observation. Piezoelectric coefficient d32 is also found to be 114% higher. In addition, we notice that poling along [111] direction does not lead to the optimal domain configuration, since barium titanate poled along [110] direction has much higher d32 and d33. The analysis reveals that much higher electromechanical coupling can be obtained in ferroelectric crystals with engineered domain configurations, and offers insight on the design and optimization of ferroelectrics for enhanced functional properties.

On the Polar Structural Fragments in Glasses from Dielectric Spectroscopic Data

The dielectric spectra of vitreous, glass-ceramic, and single-crystal Pb5Ge3O11 are measured in the frequency ranges 3–33 and ∼ 30–1000 cm–1. The inference is made that the Pb5Ge3O11 glass can represent a polar medium in which the origin of dipoles is associated with the spatial inhomogeneity and the possible existence of crystal-like structural nanofragments that had time to form during cooling of the melt and are responsible for the medium-range order in the glass. This assumption is confirmed by the fact that low-frequency (at 30 cm–1) values of e"" for the glass and the crystal along the polar axis are equal to each other and that the permittivity e""s of the glass (20.7) at submillimeter frequencies is intermediate between the permittivities e" of the crystal along the polar (34.3) and nonpolar (19.5) axes. Such a ratio between the permittivities e"s of a crystal and a glass of the same composition is revealed for the first time owing to the high accuracy in measurements of the spectrum in the submillimeter region and strong anisotropy of the Pb5Ge3O11 crystal. At the same time, the close values of the permittivities e"s for the glass and the crystal along the nonpolar axis indicate that polar atomic groupings in the glass are disordered and their structure on the nanoscale only resembles the structural motif of the crystal. The presence of microcrystals in the Pb5Ge3O11 glass-ceramics leads to a noticeable increase in the permittivity e" (∼ 25). The similarity between the IR spectra of all the Pb5Ge3O11 crystalline modifications studied and the spectrum of a glass of the same composition (with due regard for the diffuseness of the spectrum of the glass) suggests that the glass and its crystalline analog have similar short- and medium-range order structures.

Transverse electric field effect in ferroelectrics with hydrogen bonds

The results of measurements of the hysteresis loop and the depolarization electric current density along the non-polar axes directions in uniaxial ferroelectrics with hydrogen bonds have been discussed. It has been concluded that the prolonged transverse electric field permanently changes dielectric properties of the triglycine sulfate and the Rochelle Salt crystals. No analogous effects have been observed in KDP, however.