Structural study of Pb(Fe2/3W1/3)O3–PbTiO3 system (original) (raw)
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Polymorphic and morphotropic phase transitions in Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solutions
Ceramics International
Study of evolution of ferroelectric correlations in a system which intrinsically exhibits short range polar order in the form of polar-nano regions (PNRs), is the goal of the present work. For this purpose, well-known Relaxor ferroelectric i.e. PbMg Nb O 1/3 2/3 3 (PMN) and its solid solutions with PbTiO 3 (PT) has been systemically synthesized by varying composition, precursors and synthesis parameters. Dynamics associated with the PNRs and structural phase transitions of various polymorphs have been traced through temperature and frequency dependent dielectric permittivity profile. Formation of solid solutions with PT generates ferroelectric correlations associated with the tetragonal polymorphs, suppresses thermal fluctuations, overcomes diffused character of phase transition, effects polarization switching, stabilizes ferroelectric hysteresis characteristics and shifts dielectric permittivity maxima toward higher temperatures. Addition of PT led to relaxation dynamics associated with the multiple polymorphic phase transitions for T < 500 K, where system exhibits intrinsic character. Polymorphs with low symmetries lies below freezing temperature, where structural phase transition generates polar order. Diffusivity and activation energy of phase transitions, and freezing temperatures of polar regions of various processes have been quantified and compared as a function of PT. Excellent ferroelectric response of the compositions lying in the vicinity of the Morphotropic phase boundary composition has been observed. 1/3 2/3 3-PbTiO 3 (PMN-PT) solid solutions possesses peculiar structural and dipolar relaxation dynamics [12,13]. PMN-PT compositions lying in morphotropic phase boundary (MPB) range have been of a great interest due to the usage in various applications [14,15]. The microstructure of polycrystalline ceramics is direct function of the powder processing. Several factors, such as size and morphology of powder particles, chemical and structural homogeneities and grain growth are intimately related to
Phase diagram of the relaxor ferroelectric(1−x)Pb(Zn1/3Nb2/3)O3−xPbTiO3
Physical Review B, 2002
Recently, a new orthorhombic phase has been discovered in the ferroelectric system (1 − x)Pb(Zn 1/3 Nb 2/3)O3-xPbTiO3 (PZN-xPT) for x= 9%, and for x= 8% after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations, 10% ≤ x ≤15%. The orthorhombic phase was observed for x= 10%, but, surprisingly, for x ≥11% only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near vertical phase boundaries on both sides. This orthorhombic symmetry (MC-type) is in contrast to the monoclinic MA-type symmetry recently identified at low temperatures in the Pb(Zr1−xTix)O3 (PZT) system over a triangle-shaped region of the phase diagram in the range x= 0.46-0.52. To further characterize this relaxor-type system neutron inelastic scattering measurements have also been performed on a crystal of PZN-xPT with x= 15%. The anomalous soft-phonon behaviour ("waterfall" effect) previously observed for x= 0% and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.
2003
The microstructure and phase transition in relaxor ferroelectric Pb(Mg 1/3 Nb 2/3)O 3 (PMN) and its solid solution with PbTiO 3 (PT), PMN-xPT, remain to be one of the most puzzling issues of solid state science. In the present work we have investigated the evolution of the phase symmetry in PMN-xPT ceramics as a function of temperature (20 K < T < 500 K) and composition (0 ≤ x ≤ 0.15) by means of high-resolution synchrotron x-ray diffraction. Structural analysis based on the experimental data reveals that the substitution of Ti 4+ for the complex B-site (Mg 1/3 Nb 2/3) 4+ ions results in the development of a clean rhombohedral phase at a PT-concentration as low as 5%. The results provide some new insight into the development of the ferroelectric order in PMN-PT, which has been discussed in light of the kinetics of polar nanoregions and the physical models of the relaxor ferroelectrics to illustrate the structural evolution from a relaxor to a ferroelectric state.
Journal of Physics: Condensed Matter, 2001
The structure of (1 − x)[Pb(Mg 1/3 Nb 2/3 )O 3 ]-xPbTiO 3 is tetragonal and rhombohedral for x 0.35 and x 0.30, respectively. The intrinsic width of the morphotropic phase boundary region (0.30 < x < 0.35) is an order of magnitude smaller than hitherto believed. The structure of the morphotropic phase for x = 0.34 is shown to be monoclinic with space group P m and not a mixture of rhombohedral and tetragonal phases.
Phase Transitions
We revisit the phase diagram of the relaxor ferroelectric PMN-xPT using neutron powder diffraction to test suggestions that residual oxygen vacancies and/or strain affect the ground state crystal structure. Powdered samples of PMN-xPT were prepared with nominal compositions of x = 0.10, 0.20, 0.30, and 0.40 and divided into two identical sets, one of which was annealed in air to relieve grinding-induced strain and to promote an ideal oxygen stoichiometry. For a given composition and temperature the same structural phase is observed for each specimen. However, the distortions in all of the annealed samples are smaller than those in the as-prepared samples. Further, the diffraction patterns for x = 0.10, 0.20, and 0.30 are best refined using the monoclinic Cm space group. By comparing our neutron diffraction results to those obtained on single crystals having similar compositions, we conclude that the relaxor skin effect in PMN-xPT vanishes on the Ti-rich side of the morphotropic phase boundary.
Physical Review B, 2006
Dielectric, piezoelectric resonance frequency, and powder neutron diffraction studies as a function of temperature have been performed on several compositions of ͑1−x͓͒Pb͑Mg 1/3 Nb 2/3 ͒O 3 ͔-xPbTiO 3 ͑PMN-xPT͒ ceramics in and outside the morphotropic phase boundary ͑MPB͒ region to investigate the phase transitions and phase stabilities in this mixed system. Anomalies in the temperature dependence of piezoelectric resonance frequency and dielectric constant are correlated with structural changes using Rietveld analysis of powder neutron diffraction data. The frequency dependent dielectric studies reveal relaxor ferroelectric behavior for x Ͻ 0.35 and a normal ferroelectric behavior for x ജ 0.35. The dielectric peak temperature and the Vogel-Fulcher freezing temperature are found to increase linearly with "x" while their difference, after decreasing linearly with x, vanishes at x = 0.35 suggesting a crossover form relaxor ferroelectric to normal ferroelectric behavior at this composition. A phase diagram of the PMN-xPT system showing the stability fields of ergodic relaxor, monoclinic M B , monoclinic M C , tetragonal and cubic phases is presented. Our results suggest the presence of a succession of three phase transitions, not reported earlier, corresponding to structural changes from the monoclinic M B to the monoclinic M C to the tetragonal to the cubic phases for 0.27ഛ x ഛ 0.30 on heating above room temperature. In addition, our studies confirm the earlier findings on transitions from the monoclinic M C to the tetragonal to the cubic phases for 0.31ഛ x ഛ 0.34 on heating above room temperature and tetragonal to monoclinic M C phase on cooling below room temperature for x = 0.36. All these transitions are found to be accompanied with anomalies either in the temperature dependence of dielectric constant or the piezoelectric resonance frequency or both. Rietveld analyses of the powder neutron diffraction data at various temperatures on a pseudorhombohedral composition with x = 0.25 suggest that the short range M B type monoclinic order present at room temperature grows to long range monoclinic order on lowering the temperature. The temperature variations of the unit cell parameters and atomic shifts are also presented to throw light on the nature of the various phase transitions in this mixed system.