Piezoelectric anisotropy–phase transition relations in perovskite single crystals

Abstract

Articles you may be interested inStructure, piezoelectric, and ferroelectric properties of BaZrO3 substituted Bi(Mg1/2Ti1/2)O3-PbTiO3 perovskite The orientation dependence of the longitudinal piezoelectric coefficient, d 33 * , is investigated as a function of temperature in BaTiO 3 and PbTiO 3 crystals using the Landau-Ginsburg-Devonshire theory. We show that a presence of the ferroelectric-ferroelectric phase transitions in BaTiO 3 leads to enhanced d 33 * along nonpolar directions. The reason for this is that in the vicinity of a phase transition temperature at which a polarization vector changes its direction ͑tetragonalorthorhombic/monoclinic, orthorhombic/monoclinic-rhombohedral͒, the shear piezoelectric coefficients become high. It is shown for all ferroelectric phases of BaTiO 3 that the shear stress deforms the crystal cell and changes the polarization direction in a similar way as the corresponding temperature-induced phase transition. The influence of the piezoelectric shear effect on the anisotropy of d 33 * is particularly pronounced in the orthorhombic/monoclinic phase where the piezoelectric shear coefficients are determined by the presence of both the high-temperature tetragonal and the low-temperature rhombohedral phases. In PbTiO 3 , which does not exhibit ferroelectric-ferroelectric phase transitions, the shear piezoelectric effect is weak and d 33 * has its maximum along the polar axis at all temperatures. These results can be generalized to include phase transitions induced by electric-field and composition variations and are valid for all perovskite materials, including complex relaxor-ferroelectric perovskites that have recently attracted attention for their exceptionally large piezoelectric properties.

Effects of tricritical points and morphotropic phase boundaries on the piezoelectric properties of ferroelectrics

“…7,8,12 This is done at each point of the c − τ parameter space in the We start with a set of parameters which gives rise to a single tricritical point located at the triple point and a vertical MPB. For the parameter a ′ 6 we choose the value given in Eq.…”

“…[7][8][9][10][11] While polarization extension is usually the dominant mechanism in phase transitions from a nonpolar to a polar phase, such as the paraelectric cubic to ferroelectric tetragonal in BaTiO 3 , the polarization rotation mechanism is dominant in phase transitions between two polar phases with different crystal symmetry and different orientation directions of the polarization vector, such as the composition driven rhombohedral to tetragonal phase transition in PZT. 12,13 These ideas have led to the suggestion of a phase diagram which takes advantage of both mechanisms simultaneously by introducing a polar phase between another polar phase of a different symmetry and a nonpolar phase in a narrow region of the temperature-composition parameter space. 13 The large piezoelectric response in the lead-free solid solution Ba(Ti 0.8 Zr 0.2 )O 3 -(Ba 0.7 Ca 0.3 )TiO 3 (BZT-BCT) recently reported by Liu and Ren 14 has also been analyzed in terms of characteristic features of the phase diagram.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…This implies that the divergence of shear components of the elastic compliance 44 = 55 at the O to T phase boundary is much steeper than the divergence of 55 = 66 at the O to R phase boundary. 415,416 This result can be qualitatively explained by enhanced elastic shear occurring in the yz or xz planes due to the transition from the T to the O phase rather than in the transition from the O to the R phase. In other words, as reorients between [100] and [110] directions, higher shear components are encountered than when reorients between [110] and [111] directions.…”

“…For the case of PbTiO 3 , for instance, which exhibits only a T ferroelectric phase below , the shear effect described is absent. 416 In this case, other competing instabilities such as the FD longitudinal instability of or an AFD rotational instability of octahedra may be the source of strain mechanism enhancement. Although these implications are mostly relevant for intrinsic contributions, extrinsic contributions are in close relation to these instabilities since switching can in fact be considered as a collective instability of , although it also depends on extrinsic factors.…”

“…This reasoning leads to a possible generalization: the different responses of the shear components of elastic compliance across differing types of phase boundaries involving a transverse instability of are important considerations in attaining a maximized electromechanical response. 187,416 If a change in composition and/or temperature leads to a transition from a T phase to a lower symmetry phase (such as O or M), an increase of shear constants is expected that is much more pronounced that it would be at a transition from a R phase to one of these lower symmetry phases. Maximization of intrinsic piezoelectric properties will be attained at phase boundaries that feature reduced free energy anisotropy, high softening, and high ( ).…”