Domain Processes in Lead Titanate Zirconate and Barium Titanate Ceramics

Abstract

The amount of 90° reorientation during poling was determined from mechanical strains measured during the poling process. With tetragonal lead titanate zirconate 53% of the possible 90° reorientation occurred during poling, but this figure dropped to 44% upon removal of the poling field. With barium titanate the figures are only 17% and 12%, respectively. Comparison of the polarization of poled polycrystalline barium titanate with that for single crystals indicates that 180° reorientation is virtually perfect. Application of very high compressive stress parallel to the polar axis causes 90° switching of nearly all aligned domains, and, therefore, removes virtually all polarization. Curves of released charge as function of mechanical strain are nearly linear, but curves of released charge as function of stress are strongly nonlinear. Application of high compressive stress perpendicular to the polar axis also causes 90° domain reorientation and a reduction in the total polarization of the ceramic. This domain reorientation may be interpreted as a shift of the polar axes of some domains into a position more closely corresponding to the plane of cross expansion, and typically the total electric moment is reduced by less than 10%. High electric stress causes 180° as well as 90° domain reorientation. With prepoled specimens dc fields in the same direction as the poling field cause 90° switching, while reverse dc fields cause both 90° and 180° reorientation, with the latter predominating.

Thermal activation of ferroelectric switching

“…͑A reflection stacking fault for head to head, or tail to tail, non-180°domains and a rotation stacking fault for head to tail and 180°domains.͒ The width of domain walls have been reported as being in the range of 1-10 nm. [1][2][3][4][5][6]9,10 The atomic offsets and misalignments that generate the diffuse and distorted structure of these domain boundaries have been confirmed both by transmission electron microscopy investigations [20][21][22] and ab initio calculations. 23 It has been suggested that this structure makes the domain walls highly mobile and, by implication, favorable sites for the formation of steps and domain nucleation.…”

“…Although for the formulation of the problem there is no need to specify a priori the nature and configuration of the nuclei nor their nucleation sites, we shall justify the view, shared by other researchers, that domain walls are the preferred sites for their nucleation. [1][2][3][4][5][6][7][8][9][10][11][12][13] To support this view, we note that domain boundaries in ferroelectrics, which have noncentrosymmetric crystal structure, cannot be coherent planes. Instead they have to be a region of finite thickness, where the atomic displacements, adding up to a crystallographic twin stacking fault, are spread over several parallel atomic planes.…”

“…The sites where the nucleation of the new domains occurs has been a matter of some speculation, but there is a general consensus that imperfections of some kind, probably domain walls, are the preferred sites. [1][2][3][4][5][6][7][8][9][10] Earlier calculations indicated that the formation of spike shaped nuclei with reverse polarization would require an implausibly large activation energy ͑of the order of 10 8 kT͒, 6 so that even if these nuclei were able to expand with the help of thermal fluctuations, the critical field or stress needed to produce switching would be extremely high; much higher than is experimentally observed in many ferroelectric materials. In order to overcome this difficulty and help to explain how nuclei of reversed polarization can come into existence, some effects that could decrease the nucleation energy have been invoked by other researchers, among these: crystal inhomogeneities, weak spots, lattice defects, surface layer, and small residual nuclei.…”

Strain on ferroelectric thin films

“…Uniaxial pressure has been applied to zirconate-rich compounds [49,50] and morphotropic compositions in order to study the reorientation of the domains [51]. Corresponding calculations have been carried out on monodomain lead titanate, phenomenologically [52] as well as by first-principles [53], pointing out the resulting enhancement of the piezoelectric coefficient along the polar axis.…”

Nonlinearity and Scaling Behavior in a Ferroelectric Materials

“…Increasing the levels of electric field or stress leads to a depoling that results in the degradation of the dielectric and piezoelectric performances. This latter phenomenon is usually considered to be due to the irreversible motion of the domain walls [4][5][6][7][8][9][10][11]. The resulting nonlinear and hysteretic nature of piezoelectric materials induces a power limitation for heavy duty transducers or a lack of controllability for positioners.…”