Powder neutron diffraction study of phase transitions in and a phase diagram of (1-x)[Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}]-xPbTiO{sub 3}

Journal Article · Sat Jul 01 00:00:00 EDT 2006 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.74.024101· OSTI ID:20853323

Singh, Akhilesh Kumar; Pandey, Dhananjai; Zaharko, Oksana ^[1]

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1. School of Materials Science and Technology, Institute of Technology, Banaras Hindu University, Varanasi-221 005 (India)

Dielectric, piezoelectric resonance frequency, and powder neutron diffraction studies as a function of temperature have been performed on several compositions of (1-x)[Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}]-xPbTiO{sub 3} (PMN-xPT) ceramics in and outside the morphotropic phase boundary (MPB) 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<0.35 and a normal ferroelectric behavior for x{>=}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{sub B}, monoclinic M{sub 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{sub B} to the monoclinic M{sub C} to the tetragonal to the cubic phases for 0.27{<=}x{<=}0.30 on heating above room temperature. In addition, our studies confirm the earlier findings on transitions from the monoclinic M{sub C} to the tetragonal to the cubic phases for 0.31{<=}x{<=}0.34 on heating above room temperature and tetragonal to monoclinic M{sub 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{sub 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.

• OSTI ID: 20853323
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 74, Issue 2; Other Information: DOI: 10.1103/PhysRevB.74.024101; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
CERAMICS
CONCENTRATION RATIO
COOLING
FERROELECTRIC MATERIALS
FREQUENCY DEPENDENCE
HEATING
LEAD COMPOUNDS
MAGNESIUM COMPOUNDS
MONOCLINIC LATTICES
NEUTRON DIFFRACTION
NIOBATES
PERMITTIVITY
PHASE DIAGRAMS
PHASE STABILITY
PIEZOELECTRICITY
POWDERS
RESONANCE
TEMPERATURE DEPENDENCE
TITANATES