Constriction of the polarization by incoherent oxygen octahedral tilting in rhombohedral-structured lead zirconate titanate

Abstract

Double hysteresis loops have been observed in ferroelectric lead zirconate titanate ceramics with a Zr/Ti ratio of 65/35 (PZT 65/35). In addition, dielectric dispersion was found near 50 °C, corresponding to the high-temperature to low-temperature rhombohedral ferroelectric [FER(HT)-FER(LT)] transformation. Structurally this transformation is an oxygen octahedra tilting along the 〈111〉. It is proposed that an inability of the oxygen octahedra to coherently rotate within a rigid lattice generates random internal stresses which constrain the polarization. Small amounts of impurities on either the A site (La) or B site (Nb) were found to result in normal square-loop hysteresis behavior. It is believed that aliovalent impurities relax the lattice, resulting in increased coherent of the 〈111〉 oxygen rotations. Electron diffraction studies revealed a strong increase of the reflection intensity of 1/2〈111〉 superlattice spots after doping, supporting this possibility. In addition, thermal expansion measurements revealed a lattice contraction after La-modification, possibly reflecting enhanced octahedral tilting.

Double hysteresis loop induced by defect dipoles in ferroelectric Pb(Zr0.8Ti0.2)O3 thin films

“…3 It is well known that the presence of defect dipoles (DDs), for instance, formed by the association of oxygen vacancies with metal impurities (such as Fe, Mn, Ni, and Cu), strongly influences the properties of ferroelectric materials such as polarization, aging, conductivity, and fatigue. [4][5][6][7][8][9][10][11] For instance, the effect of aliovalent dopants on PbTiO 3 , such as Fe 3þ , leads to the creation of oxygen vacancies (V O ) for charge compensation ðFe 0 Ti À V O Þ that are expected to have a major impact on properties and performance of ferroelectric compounds. 12 Lambeck and Jonker further suggested that defect-dipole alignment can occur along the direction of the spontaneous polarization in reduced BaTiO 3 single crystals, thus proposing that the aging phenomenon is due to a gradual alignment of a doubly positively charged oxygen vacancy associated defect dipoles in the perovskite lattice.…”

Raman scattering study on ferroelectric (Ba0.32Sr0.68)2Nb2O7 ceramics

“…When A-site doped with ions, which has smaller ionic radii than A-site ions, firstly, the lattice would shrink and the octahedra will tilt upon further increasing the doping ratio [17,18]. It is a common concept that the changes of Ba ions in BaTiO 3 to the Sr ions cause octahedra tilting in the ferroelectric phase.…”

Pressure‐driven phase transition and energy conversion in ferroelectrics: Principles, materials, and applications

“…This phenomenon has also been observed in other PZT‐based materials, and it is generally believed that this transformation is driven by the softening of the Γ 25 optical mode at the first Brillouin zone boundary, which results in the rotation of the oxygen octahedra along the 〈1 1 1〉 direction in the FE LTR . At high temperatures, the thermal energy disturbs the uniform rotation of the oxygen octahedra, thus resulting in random internal stress, and this decoupling causes a drop in the polarization 58,59 . Oh et al.…”

“…At high temperatures, the thermal energy disturbs the uniform rotation of the oxygen octahedra, thus resulting in random internal stress, and this decoupling causes a drop in the polarization. 58,59 Oh et al reported that the FE LTR-HTR phase-transition temperature decreases on increasing the tensile hydrostatic pressure, which is attributed to the suppressed oxygen rotation. 52 In contrast to the case of tensile stress, the opposite tendencies occur under compressive stress, wherein compressive hydrostatic pressure can improve the FE LTR-HTR transition temperature.…”