Effect of oxygen pressure on the grain and domain structure of polycrystalline 0.85PbMg_1/3Nb_2/3O₃–0.15PbTiO₃ thin films studied by scanning probe microscopy

Abstract

0.85PbMg1/3Nb2/3O3–0.15PbTiO3 ferroelectric–relaxor thin films have been deposited on La0.5Sr0.5CoO3/(1 1 1) Pt/TiO2/SiO2/Si by pulsed laser ablation at various oxygen partial pressures in the range 0.05 to 0.4 Torr. All the films have a rhombohedral perovskite structure. The grain morphology and orientation are drastically affected by the oxygen pressure, studied by x-ray diffraction and scanning electron microscopy. The domain structure investigations by dynamic contact electrostatic force microscopy have revealed that the distribution of polar nanoregions and their dynamics is influenced by the grain morphology, orientation and more importantly, oxygen vacancies. The correlation length extracted from autocorrelation function images has shown that the polarization disorder decreases with oxygen pressure up to 0.3 Torr. The presence of polarized domains and their electric field induced switching is discussed in terms of internal bias field and domain wall pinning. Film deposited at 0.4 Torr presents a curious case with unique triangular grain morphology and large polarization disorder.

Mesoscale Domains and Nature of the Relaxor State by Piezoresponse Force Microscopy

“…Piezoresponse force microscopy (PFM) (22)(23)(24) has been especially successful because of its intrinsically high resolution and the ability to follow the polarization statics and dynamics via a local piezoresponse. Researchers have studied several classes of relaxor materials, including single crystals [e.g., SBN (25)(26)(27)(28), PbMg 1/3 Nb 2/3 O 3 -PbTiO 3 (PMN-PT) (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40), and PbZn 1/3 Nb 2/3 O 3 -PbTiO 3 (PZN-PT) (41,42)], ceramics [e.g., (Pb,La)(Zr,Ti)O 3 (PLZT) (43)(44)(45), PMN-PT (46), and some lead-free compositions (47)(48)(49)], and thin films (50)(51)(52)(53). This review is devoted to the recent advances in PFM studies of relaxors and to a further understanding of the mechanisms of polarization behavior in these emergent functional materials.…”