The phase transitions of Pb1−xSrx(Al1/3Nb2/3)0.1(Zr0.52Ti0.48)0.9O3 (Sr-modified PAN-PZT) ceramics with Sr compositions of x = 2%, 5%, 10% and 15% have been investigated using X-ray diffraction (XRD), temperature dependent dielectric permittivity and Raman scattering. The XRD analysis show that the phase transition occurs between Sr composition of 5% and 10%. Based on the broad dielectric peaks at 100 Hz, the diffused phase transition from tetragonal (T) to cubic (C) structure shifts to lower temperature with increasing Sr composition. The dramatic changes of wavenumber and full width at half-maximum (FWHM) for E(TO4)′ softing mode can be observed at morphotropic phase boundary (MPB). Moreover, the MPB characteristic shows a wider and lower trend of temperature region with increasing Sr composition. It could be ascribed to the diminishment of the energy barrier and increment of A-cation entropy. Therefore, the Sr-modified PAN-PZT ceramics unambiguously undergo two successive structural transitions (rhombohedral-tetragonal-cubic phase) with temperature from 80 to 750 K. Correspondingly, the phase diagram of Sr-modified PAN-PZT ceramics can be well depicted.
An electric-field induced giant strain response and doping level dependent domain structural variations have been studied in the dysprosium (Dy3+)-modified 0.935(Na1/2Bi1/2)TiO3-0.065BaTiO3(xDy : NBBT) ceramics with the doping levels of 0%, 0.5%, 1%, and 2%. X-ray diffraction and Raman spectroscopy analyses not only demonstrates the change in ionic configurations induced by Dy3+ doping, but also shows the local crystal symmetry for x ≥ 0.5% doping levels to deviate from the idealized cubic structure. Piezoresponse force microscopy measurement exhibits the presence of an intermediate phase with orthorhombic symmetry at the critical Dy3+ doping level of 2%. Moreover, at this doping level, a giant recoverable nonlinear strain of ∼0.44% can be observed with high normalized strain (Smax/Emax) of 728 pm/V. At the same applied field, the strain exhibits a 175% increase than that of NBBT ceramic. Such a large strain stems from the varying coherence lengths of polar nanoregions (PNRs) and an unusual reversible 90° domain switching caused by the symmetry conforming property of point defects, where the restoring force is provided by unswitchable defects. The mechanism reveals a new possibility to achieve large electric-field strain effect for a wide range of ferroelectric systems, which can lead to applications in novel “on-off” actuators.
Highly (222)-oriented 90%Pb(Zn 1/3 Nb 2/3 )O 3 -10%PbTiO 3 (abbreviated PZN-PT) thin films, about 550nm in thickness, have been successfully grown on (111)Pt/Ti/SiO 2 /Si substrate by pulsed laser deposition method. Pure pyrochlore phase with highly (222)-preferred orientation, determined by X-ray diffraction, was formed in the PZN-PT thin films when the temperature of substrates is 550 °C. FE-SEM investigation shows that the surface appearance and the cross section of the films are smooth and crack-free with some dispersive spherical protrusions. The dielectric constant and loss of the thin films were measured using an impedance analyzer (HP4194A). The dielectric constant ( r ε ) and the dissipation factor ( tanδ ) at 1 kHz are 205 and 0.03, respectively.
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