Enhancement of polar nature of domain boundaries in ferroelastic Pb₃(PO₄)₂ by doping divalent-metal ions

Abstract

The effect of doping metal ions in ferroelastic Pb 3 (PO 4 ) 2 (PPO) on the polar nature of domain boundaries (DBs) was investigated using a second harmonic generation (SHG) microscope. It has been already reported that (DBs) of non-doped PPO is SH active and polar. The present study reveals that DBs of Ca-doped and Mg-doped PPO show greatly enhanced SH activity. This indicates that doping by metal ions enhances the polar nature of the DBs of PPO. This is important for future applications of DB nanotechnology. The enhancement of SH intensity is explained by a larger displacement of Ca 2+ and Mg 2+ ions in DBs due to smaller ionic radii. Analyses of the SH anisotropy experiments reveal that the symmetry-adapted W-wall belongs to monoclinic m and the non-adapted W'-wall to monoclinic 2. Both point groups are classi ed as the polar classes, which coincides with the case of pure PPO.

Ferroelastic Twinning in Minerals: A Source of Trace Elements, Conductivity, and Unexpected Piezoelectricity

“…The energy exponent of the mobile twin walls ε increases from ~1.44 to 2.0 when the vacancy concentration increases. Such enrichments of cations and vacancies in twin walls have been widely reported in the literature (e.g., in perovskites [37], klinker [48], twinned alloys [49], pure metal twin walls [50], cassiterite (SnO2) [51], tellurized molydenite [52], tungsten dichalcogenites [53], and twin wall doping in palmierite [54]. Oxygen vacancy trapping in perovskite was simulated and the results are discussed in [55,56].…”

“…Another useful method is phonon spectroscopy [75,76]. Polar twin walls were also confirmed in other minerals, such as palmierite [31,54] and clinobisvanite BiVO 4 [77,78]. Very high densities of twin walls, such as in tweed structures, lead to an overall SHG background that proves that the mineral contains an extremely high density of walls that is hard to see using other techniques [79].…”

Domain-wall engineering and topological defects in ferroelectric and ferroelastic materials

“…So far, the point group symmetry has mainly been probed by SHG [71][72][73][74][75] , performing a polarisation analysis of the incident and emitted light fields. This approach has produced remarkable results, starting with the experimental confirmation of the non-centrosymmetric symmetry of strain-compatible ferroelastic walls [71][72][73][74][75] , but also observations that are at odds with the classical theoretical approaches. In calcium titanate (CaTiO3), domain walls were found that have, according to the SHG analysis, a polar axis deviating from the predicted possible directions (FIG.…”

“…Recent experimental works on polar domain walls have concentrated on demonstrating the loss of inversion symmetry 34,[71][72][73][74][75] , quantifying domain wall polarisation by structural studies 81 , and looking for evidence for characteristic electric or dielectric signatures of this domain wall polarisation 11,33,34,82,83 .…”