Sharp Ferroelectric Phase Transition Research Articles

X-ray diffraction study revealing phase coexistence in barium titanate stannate

In this paper, the results of a temperature dependent x-ray diffraction (XRD) study on BaTi0.95Sn0.05O3 (BTS-5) ceramics are compared with dielectric measurements. The orthorhombic-tetragonal phase transition at T2 = 306 K is found to proceed in a considerably wider temperature range than expected from the dielectric anomaly. Although the macroscopic properties of BTS-5 indicate a rather sharp ferroelectric phase transition at Tc = 358K, we observe anomalous XRD-patterns in a 25 K wide temperature range. This is interpreted in terms of mechanically clamped tetragonal and cubic phase, coexisting in the vicinity of Tc in grains with inhomogeneous Sn-distribution.

Structural and Electrical Properties of Magnesium Tellurite Ceramics

Polycrystalline samples of MgTeO 3 were prepared by a conventional solid-state reaction technique at 750°C. An X-ray powder diffraction (XRD) technique was used to check the formation of a single phase MgTeO 3 compound with cell parameters a = 4.421(1) Å, b = 14.916(1) Å and c = 12.289(1) Å in an orthorhombic crystal system. Detailed studies of dielectric and electrical properties show that the compound has a sharp ferroelectric phase transition of first order.

Field-induced sharp ferroelectric phase transition in Sr0.66Ba0.34Nb2O6 relaxor ferroelectric

Field-induced sharp ferroelectric phase transition was observed in Sr0.66Ba0.34Nb2O6 single crystals. The peaks of the real and imaginary parts of dielectric permittivity arise upon cooling under weak dc bias electric fields and subsequently heating under zero fields or upon cooling under zero fields and subsequently heating under weak electric fields. The applied electric field cancels the random fields that destroy the phase transition and give rise to low temperature domain state if E=0. These results strongly suggest that the SBN system belongs to the random field Ising universality class, a rare case among structural phase transitions.

Hypersonic frequency softening and relaxation in relaxor ferroelectric 0.8Pb(Zn 1/3Nb 2/3)O 3–0.2PbTiO 3

Brillouin scattering from relaxor ferroelectric 0.8Pb(Zn 1/3Nb 2/3)O 3–0.2PbTiO 3 has been measured in the 300–723 K temperature range. A sharp ferroelectric phase transition from cubic to tetragonal symmetry, associated with a phonon frequency dip and a Landau–Khalatnikov-like damping maximum, has been observed near 528 K. Evidence for a relaxation mode in the form of a broad Rayleigh wing, whose frequency is strongly temperature dependent above 528 K, is found. The relaxation time and frequency are evaluated based on the tunneling model and a modified-superparaelectric model, respectively.

Dieletric and relaxation behaviors of (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 single crystal

Dielectric permittivity along the [111] direction has been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 (PMN-33%PT). A sharp ferroelectric phase transition was observed near 425 K and 429 K for cooling and heating processes, respectively. As temperature decreases, a diffuse phase transition (which begins near 330 K upon cooling) was detected. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 330 and 425 K upon cooling) are diffuse first-order and first-order, respectively. The frequency-dependent dielectric data ε′111 (ƒ, T) prove the existence of an electric dipolar relaxation process between 350 and 400 K. The activation energy, the Vogel-Fulcher temperature and attempt frequency corresponding to this relaxation process are also calculated.

Hypersonic and dielectric properties of (PbZn1/3Nb2/3O3)0.915–(PbTiO3)0.085 single crystal

Both the longitudinal Brillouin backscattering spectra and dielectric permittivities along the [001] direction have been measured as a function of temperature for a relaxor ferroelectric single crystal (PbZn1/3Nb2/3O3)0.915–(PbTiO3)0.085 (PZN–8.5%PT). A sharp ferroelectric phase transition (which is associated with a Landau–Khalatnikov-type phonon damping maximum) was observed near 450 K. As temperature deceases, a diffuse phase transition (which is associated with a broad acoustic phonon damping maximum) was detected near 355 K. This broad damping evolution is attributed to dynamic order-parameter fluctuations. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 355 and 450 K) are diffuse first order and first order, respectively. The frequency-dependent dielectric data εc″(f,T) prove the existence of an electric dipolar relaxation process below 360 K. The activation energy, the Vogel–Fulcher temperature, and attempt frequency corresponding to this relaxation process are also calculated.

Hypersonic and dielectric anomalies of(Pb(Zn1/3Nb2/3)O3)0.905(PbTiO3)0.095single crystal

Both the longitudinal (LA) Brillouin backscattering spectra and dielectric permittivities along the [001] direction have been measured as a function of temperature for relaxor-ferroelectric single-crystal ${(\mathrm{P}\mathrm{b}(\mathrm{Z}\mathrm{n}}_{1/3}{\mathrm{Nb}}_{2/3}{)\mathrm{O}}_{3}{)}_{0.905}{(\mathrm{P}\mathrm{b}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}{)}_{0.095}$ (PZN-9.5%PT). A sharp ferroelectric phase transition (which is associated with a sharp Landau-Khalatnikov-like phonon damping maximum) was observed near 460 K. As the temperature decreases, a diffuse phase transition (which is associated with a broad acoustic phonon damping maximum) was detected near 340 K. This broad damping evolution is attributed to dynamic order-parameter fluctuations. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 340 and 460 K) are diffuse first order and first order, respectively. The frequency-dependent dielectric data ${\ensuremath{\varepsilon}}_{c}^{\ensuremath{''}}(f,T)$ prove the existence of an electric dipolar relaxation process below 360 K. The activation energy, the Vogel-Fulcher temperature, and attempt frequency corresponding to this relaxation process are also calculated.

Hypersonic and Dielectric Studies of Relaxor Ferroelectric Single Crystal

AbstractBoth the longitudinal (LA) Brillouin back-scattering spectra and dielectric permittivity along the [001] direction have been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg1/3Nb2/3O3)0.68(PbTiO3)0.32 (PMN-32%PT). A sharp ferroelectric phase transition (which is associated with a Landau-Khalatnikov-like phonon damping maximum) was observed near 445 K. As temperature increases, a diffuse phase transition was detected near 280 K. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 280 and 445 K for heating procedure) are diffuse first-order and first-order, It respectively. The dielectric data prove the existence of an electric dipolar relaxation process below 300 K.

Relaxorferroelectrics: An overview

Abstract The paper will trace the evolution of understanding related to the modification of sharp ferroelectric phase transition behavior that occurs in composition systems which exhibit diffuse and relaxor ferroelectric properties. The focus will be primarily upon the perovskite structure families where cations of different valence occupying similar crystallographic sites in the structure appear to play an important role. Limited ordering in the Pb(B1B2)O3 systems will be discussed and possible mechanisms for self limiting to nanometer scales in some systems explored. New studies of the break up of the simple ferroelectric behavior in lanthanum modified lead zirconate titanate (PLZT) and in lead titanate (PLT) systems will be discussed and the relevance to the general problem of relaxor behavior examined. Evidence for enhanced polarization fluctuations and super paraelectric behavior at high temperatures will be discussed and random field and spin glass models for the lower temperature state considered. ...

Phenomena at transformation from sharp to diffuse ferroelectric phase transition

Abstract Transformation of the sharp ferroelectric phase transition into diffused one observed in some solid solutions at the change of the component concentration is followed and caused by decrease of size of the polar regions formed at the local phase transitions. Most important changes of the state seem to have taken place when the size of polar regions is near to the domain width.