Mechanical Polishing Effects Toward Surface Domain Evolution in Pb(Zn_(1/3)Nb_(2/3))O_3-PbTiO_3 Single Crystals

摘要

This paper presents the mechanical polishing effects on the surface domains and crystal structures of relaxor-based Pb(Zn_(1/3) Nb_(2/3))O_3-PbTiO_3 (PZN-PT) single crystals. In normal sample preparation processes, a "surface deformed layer" composed of distorted crystal structures is produced due to intense compression caused by several polishing steps using a series of lapping films down to 1 urn in particle size. This "surface deformed layer" may contribute to dissimilar properties compared with those of the interior, and also result in pop-in events in the load-displacement curve (P-h curve) during nanoindentation. An anomaly in the X-ray diffraction (XRD) profiles is also found, demonstrating a broad minor peak besides the major peak in the intensity. In addition, Piezoresponse Force Microscopy reveals that the domain structures on the crystal surface appear to be distorted and aligned along the polishing direction. Therefore, a controlled fine polishing procedure using AI_2O, slurry of 0.3 μm particle size is adopted to remove this "surface deformed layer." After polishing to mirror finish, the macroscopic orientations of the domain walls agree well with the permissible domain wall directions. The topography is also altered analogous with the polarization direction. More specifically, the upward domains constitute a depression of ～ 10 nm compared with the downward domains, suggesting a different hardness for the head and tail domain sections. Furthermore, the minor peak in the XRD and the pop-in event in the nanoindentation P-h curve are successfully eliminated after this fine polishing procedure. The removal of the surface layer may also lower the coercive field of the crystals, thus enabling ferroelectric control with a smaller voltage.