Nanoscale domains and preferred cracking planes in Pb(Zn1/3Nb2/3)O3–(6–7)% PbTiO3 single crystals studied by piezoresponse force microscopy and fractography

Abstract

This paper presents recent studies on surface and cross-sectional domain structures of Pb(Zn1/3Nb2/3)O3–(6–7)% PbTiO3 (PZN–PT) single crystals using piezoresponse force microscopy and three-point bending technique. The surface domain structures for the rhombohedral-based single crystals in (001) orientation are found to be influenced by polishing process, whereas the surface domains on the (011)-oriented single crystals are aligned along [011¯] direction, unaffected by the polishing process. On the other hand, the domain structures on the cross-sectional fracture surface show preferential alignment which agrees reasonably with the rhombohedral dipoles on the {100} and {110} planes. The differences between the surface and cross-sectional domain structures could be attributed to stress compensation between the surface strain effect and the minimization of elastic energy. In addition, both surface and cross-sectional surface demonstrate nanoscale domains, about 100–200 nm in size. Further fractography observation suggests that the preferred cracking planes for the PZN–PT single crystals are {110} and {100} planes. The {110} planes may be the slip planes along which material pile up is observed upon indentation loading. The pile up results in tensile hoop stress, producing radial cracks along the {100} cleavage planes. To accommodate the localized stress change, new ferroelastic domains by mechanical stress are then formed without interrupting the out-of-plane piezoelectric response. Since the material pile up is thought to cause enhanced toughness along {110} planes, the PZN–PT single crystal in [011]-poled orientation exhibits more superior piezoelectric properties compared to that of the [001]-poled counterpart.

Persistence of ferroelectricity above the Curie temperature at the surface ofPb(Zn1/3Nb2/<

“…This is therefore the thickness of the skin layer in our crystals. Second, the skin is considerably "tortured" in comparison with the bulk: simple visual inspection shows the density of dislocations to be bigger, and electron diffraction (inset) confirms the existence of considerable mosaicity; both observations are consistent with stress-induced changes due to sample polishing, as proposed by Wong and Zeng [14,15]. We parenthetically note that polishing stress has been shown to induce the appearance of polar modes in otherwise centrosymmetric materials such as CaWO 4 and CaMoO 4 [32].…”

“…While initial evidence suggested that the skin had different symmetry from the bulk [19], later studies by Kisi and Forrester [20] detected no difference in symmetry, prompting the authors to suggest that the difference between bulk and surface may just be in the domain state. The surface domains have themselves been variously linked to polishing stress [14] and to the symmetry-breaking effect of the surface on the ordering of * gustau.catalan@cin2.es relaxor polar nanoregions [14][15][16][17][18]. There is no consensus about the thickness of the surface layer, nor about whether its phase transitions coincide with those of the bulk.…”

“…Subsequent investigations by piezoresponse force microscopy have shown that the surface possesses a mesoscopic (submicron) labyrinthine domain structure [14][15][16][17][18]. Questions and controversies surround this surface layer.…”

Unusual domain configurations and local piezoresponse in the [720]‐cut BaTiO3 single crystal

“…Such a high elastic strain energy along this special plane undoubtedly develop the unusual, regular domain walls features for stress compensation along the permissible preferred ferroelectric orientation on the [720]‐cut BT surface, while for the (001)‐oriented BT crystal in the present study, the surface stress effect due to the polish‐ ing process could prevail over the usual elastic energy effect from its tetragonality, thus gives no evidence of regular domains walls on its topography image, although appearing on its corresponding piezoresponse image. Similar behaviors were also seen in the difference between the surface domains on the top crystal surface and the internal domains on the fracture surface of the Pb(Zn 1/3 Nb 2/3 )O 3 –PbTiO 3 single‐crystal system studied by Wong and Zeng 19.…”

Origin of sawtooth domain walls in ferroelectrics

“…In bulk ferroelectrics, the domain structure, closely related to phase structure, was thoroughly discussed along with domain size and morphology. On an even smaller scale, polar nanoregions as a special type of domains have also been discussed [18][19][20][21][22][23].…”