Transparent ferroelectric ceramics PbMg1/3Nb2/3O3-xPbZr0.53Ti0.47O3: Dielectric and electro-optical properties

Lanthanum-free high-transparency ferroelectric ceramics PbMg_1/3Nb_2/3O₃?xPbZr_0.53Ti_0.47O₃ (PMN-xPZT) have been prepared for the first time by a two-stage sintering method. The dielectric and electro-optical properties of the PMN-xPZT ceramics of different compositions, with the values of x both far from the morphotropic phase boundary (x = 10, 16, 23%) and close to it (x = 33%), have been studied. It has been shown that, in compositions lying closer to the morphotropic phase boundary (x = 23 and 33%), one observes, with no electric field applied, a first-order phase transition to a macrodomain ferroelectric phase, whereas the compositions far from the boundary (x = 10, 16%) persist in the relaxor cubic phase down to the low-temperature domain. It has been found that, in the ceramic with x = 33%, the quadratic electro-optical coefficients have at high temperatures (T > 340 K) the largest value among the relaxor systems, which expands the temperature interval of applicability of these solid solutions in industry.     

Evolution of phase transitions in SrTiO3-BiFeO3 solid solutions

The dielectric and acoustic properties of (1 ? x)SrTiO₃?xBiFeO₃ solid solutions (0 ≤ x ≤ 1) have been studied in the temperature range from 4.2 to 850 K. Evolution of the antiferrodistortive transition and its suppression in the concentration range 0.1 < x < 0.2 have been revealed. X-ray diffraction data obtained at room temperature, as well as the observed acoustic anomalies combined with dielectric measurements, have been used to estimate the concentration range of the existence of the relaxor state, as well as of the formation and coexistence of the antiferromagnetic and ferroelectric phases at high BiFeO₃ concentrations.     

Phase formation and dielectric phase transition in Ba1−xCaxTi0.6Zr0.4O3 solid solutions

Perovskite types Ba_1−xCa_xTi_0.6Zr_0.4O₃ (with x=0.0-0.5) ceramics have been prepared through solid state reaction route. The room temperature XRD study suggests the compositions with x=0.0 and x=0.1 have single phase cubic symmetry. With further increase in Ca content, solid solution breaks and an orthorhombic CaTiO₃ like phase is developed. The dielectric study on single phase compositions (x=0.0 and 0.1) reveals that the materials are of relaxor type and undergo a diffuse type ferroelectric phase transition. In the Ca containing composition higher transition temperature is observed than the pure BaTi_0.6Zr_0.4O₃ materials. In the paraelectric region (above T_c) lower diffusivity is observed in the Ca containing composition. The strength of relaxation is calculated and found to be more in Ca containing material than that of pure BaTi_0.6Zr_0.4O₃ composition.     

Low-frequency dielectric relaxation (1/<Emphasis Type="Italic">f</Emphasis> noise) in relaxors of the (1 − <Emphasis Type="Italic">x</Emphasis>)PMN-(<Emphasis Type="Italic">x</Emphasis>)PZT system

The dielectric properties of relaxor ferroelectric ceramics (1 ? x)PbMg_1/3Nb_2/3O₃-(x)PbZr_0.53Ti_0.47O₃ (PMN-PZT) have been studied at frequencies from 40 Hz to 1 MHz in the temperature range of the diffuse phase transition. It is established that the dielectric relaxation generates 1/f noise, whose spectral density depends on the relaxor composition and temperature.     

Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.     

Spontaneous phase transition from relaxor to macrodomain ferroelectric state in single-crystal PbSc0.5Nb0.5O3-BaSc0.5Nb0.5O3 solid solutions

The cooling of Pb_1?x Ba_xSc_0.5Nb_0.5O₃ solid solutions with x≤0.04 leads to a spontaneous transition from a relaxor to a macrodomain ferroelectric state, accompanied by anomalous variation of the dielectric and optical properties of the material. As the barium content in the system increases, the relaxor state becomes more stable and eventually “freezes” at x≈0.05. The crystals with x=0.06 exhibited the appearance of a macrodomain ferroelectric phase induced both by an external electric field with a strength of 1.5 kV/cm and by an internal electric field formed in the course of dielectric aging.     

Dielectric characteristics of the relaxor state of the perovskite ceramics 0.9(Na1 − x K x Bi)1/2TiO3-0.1Bi(ZnTi)1/2O3 near the morphotropic phase boundary

X-ray diffraction investigations have revealed that, in the system of solid solutions 0.9(Na_{1 ? x} K _x Bi)_1/2TiO₃-0.1Bi(ZnTi)_1/2O₃, there is a morphotropic phase boundary in the potassium concentration range of x ≈ 0.25, which separates the regions of compositions with rhombohedral (R3c) and tetragonal (P4mm) structures. It has been shown that, in the vicinity of this boundary, ceramic samples of the studied system exhibit properties of relaxor ferroelectrics. The results of the investigation into the dielectric properties of relaxor ceramics of the composition x = 0.3 with the use of the impedance spectra measured in the frequency range from 25 to 10⁶ Hz at temperatures from 100 to 900 K have been presented. It has been found that, in the temperature region of the existence of the relaxor state lying below the temperature corresponding to the maximum of the real part of the permittivity (T′ _m = 550 K), the dielectric polarization is determined by the sum of the contributions from the matrix and dipole clusters. The temperature dependence of the contribution from the clusters, which is determined by the kinetics of their formation and freezing, is characterized by a curve with the maximum at approximately 400 K. The process of freezing of dipole clusters occurs over an extended temperature range of more than 200 K.     

Phase transitions in xPbZr0.53Ti0.47O3-(1 − x)Mn0.4Zn0.6Fe2O4 magnetoelectric composites

The elastic, inelastic, and dielectric properties of the magnetoelectric composite xPbZr_0.53Ti_0.47O₃-(1 ? x)Mn_0.4Zn_0.6Fe₂O₄ (PZT-MZF) are studied in the temperature range from room temperature to 673 K. The influence of the ferroelectric PZT phase on the magnetic phase transition and the magnetic MZF phase on the ferroelectric phase transition is revealed. It is established that, as the PZT content increases, the degree of diffuseness of the phase transition decreases and a gradual crossover from a pronounced relaxor behavior to a more ordered ferroelectric behavior occurs.     

Diffuse phase transition in Ba5NdTi3−xZrxNb7O30 ferroelectric ceramics

Polycrystalline samples of Ba₅NdTi_3−xZr_xNb₇O₃₀ (x=0, 1, 2, 3) compounds of the tungsten-bronze (TB) structural family were prepared by a high-temperature solid-state reaction technique. X-ray study of the compounds shows the formation of single phase compounds in the orthorhombic crystal system at room temperature. Detailed studies of the dielectric properties (dielectric constant and loss tangent) as a function of temperature (−50 to 350°C) at four different frequencies, 1, 10, 100 and 1000 kHz show relaxor behavior and diffuse phase transition of the compounds. Study of temperature dependence of resistivity shows that these compounds have negative temperature coefficients of resistance (NTCR).     

Ferroelectric phase transition of Ba1− x Sr x Ti0.6Zr0.4O3 ceramics

Perovskite type Ba_{1? x} Sr _x Ti_0.6Zr_0.4O₃ (with x = 0.0, 0.1, 0.2, 0.4 and 0.5) ceramics have been synthesized through solid oxide reaction route. The room temperature XRD study suggests the compositions have single phase cubic symmetry. Microstructural studies have shown a step decrease in grain size. The dielectric study reveals that the materials are of relaxor type and undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in Sr contents in the studied composition range. The transition temperature decreases with increase in Sr contents due to the decrease in grain size.     

Temperature and composition dependence of vibrational modes in Sm1−xLaxAlO3

At room temperature and for x₀ ～ 0.43, the system Sm_1?xLa_xAlO₃ undergoes a first order phase transition in which an orthorhombic structure transforms into a rhomboedral structure as x increases. This phase transition was investigated by Raman scattering experiments on polycrystalline compounds in the range 0 ? x ? 1. The dependence of low frequency modes on x is reported and compared with their well known temperature dependence. Soft modes have been observed in the orthorhombic (D_2h¹⁶) and rhomboedral (D_3d⁶) phases. It was found that the first order phase transition is probably driven by a double degenerate mode whose two components in the low symmetry phase display a linear composition dependence of their squared frequencies. The source of anomalous behaviour of Raman bands near the phase transition is discussed.     

Structural phase transitions in the Bi1−x La x FeO3 system

The crystal structure and phase composition of the Bi_1?x La _x FeO₃ system have been studied by the methods of neutron and x-ray diffractions and electron microscopy. It has been revealed that a unit cell of the solid solutions at room temperature is described by the R3c, Imma, and Pnma space groups in the concentration ranges 0 < x < 0.19, 0.4 < x < 0.5, and x > 0.5, respectively. For 0.2 < x < 0.4, the solid solutions are not formed.     

Dielectric properties and specific heat of the (1 ? x)PbNi1/3Nb2/3O3-xPbTiO3 ferroelectric ceramics

The temperature dependences of the permittivity and specific heat of a mixed (1 ? x)PbNi_1/3Nb_2/3O₃-xPbTiO₃ system (where x = 0.3, 0.4, 0.5) have been studied over a wide temperature range 290?C700 K. It has been shown that the composition with x = 0.3 undergoes a diffuse phase transition at T _m ?? 315 K. A specific heat anomaly that is characteristic of the phase transition has been revealed at T ?? 315 K in all the compositions under study.     

Investigation on optical transmission spectra of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

The optical transmission spectra from 0.3 to 11 μm of relaxor ferroelectric single crystals (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) were systematically studied at room temperature in this paper. The crystal is transparent between 0.45 and 5.5 μm and becomes completely absorbing around 0.4 μm in near UV region and 10 μm in infrared region. But the wavelength cutoff in near UV is much sharper than the long wavelength cutoff. As compared with other configurations, tetragonal single crystals possess the optimal transmission properties. The optical transmittance in the wavelength region from 0.45 to 5.5 μm is about 70%. The results show that tetragonal PMN-xPT single crystals are promising for a wide range of optical applications. Some discussions about the oxygen-octahedra structure that determines the basic energy level of the crystals are also presented on the optical properties of PMN-xPT single crystals.     

The structural and magnetic properties of Ni2Mn1−xBxGa Heusler alloys

The influence of the substitution of manganese by boron on the crystal structure and magnetic properties of Ni₂Mn_1−xB_xGa Heusler alloys with 0?x?0.5 has been investigated using X-ray diffraction, thermal expansion, resistivity, and magnetization measurements. The samples with concentrations x<0.25 were found to be of single phase and belonged to the cubic L2₁ crystal structure at room temperature. Crystal cell parameters of the alloys decreased from 5.830 to 5.825 Å with increasing boron concentration (x) from 0 to 0.25. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization decreased with increasing boron concentration. The ferromagnetic ordering and structural transition temperatures for 0?x?0.3 have been observed and the phase (x−T) diagram of the Ni₂Mn_1−xB_xGa system was constructed. The phase (x−T) diagram indicates that the ground state of Ni₂Mn_1−xB_xGa alloys belongs to ferromagnetic martensitic, premartensitic, and austenitic phases in x?0.12, 0.12<x?0.18, and 0.18<x?0.3, respectively. The relative influence of cell parameters and electron concentrations on the phase diagram is discussed.     

Raman scattering from electronic excitations of samarium in semiconducting and metallic Sm1−xYxS

The Raman spectra of Sm_1?xY_xS for $\text{x?0.4}$ have been measured. Electronic scattering between the J = 0 ground state and the J = 1 and 2 excited states of Sm²⁺ is observed. The singlet-triplet transition is observed on both sides of the black to gold phase transition in Sm_1?xY_xS.     

Lattice dynamics and low‐temperature Raman spectroscopy studies of PMN–PT relaxors

In this work we present a Raman scattering study of a specific region of the morphotropic phase boundary (MPB) of the [Pb(Mg_1/3Nb_2/3)O₃]_1−x (PbTiO₃)_x relaxor system. We performed low‐temperature measurement for the x = 0.4 composition in the 20–300 K temperature range, and a detailed analysis of Raman spectra of x = 0.4 and x = 0.37 compositions at 180 K. The analysis of Raman spectra indicates a structural phase transition at around 170 K for x = 0.4. The comparison of Raman data from x = 0.4 and x = 0.37 compositions suggests different phases for these samples at 180 K. These results are in accordance with the tetragonal to monoclinic structural phase transition observed in the PMN–PT MPB and contribute to improve the knowledge of the MPB of this solid solution. Additionally, we have performed the lattice dynamics phonon calculation of the (1 − x) PMN–xPT relaxor in order to best understand its complex Raman spectral properties. The normal mode analyses (at q ∼ 0) were performed by considering tetragonal symmetry for the (1 − x) PMN–xPT system and using the rigid ion model and mean field approximation. Our calculated wavenumber values are in good agreement with experimental and calculated results reported for PbTiO₃ thus providing a reliable assignment of the various Raman modes. The low wavenumber modes are interpreted as arising from a lifting of the degeneracy of the vibrational modes related to Mg, Nb and Ti sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Relaxor behavior of SrTiO3-LiNbO3 solid solutions

Ceramic samples of (1 ? x)SrTiO₃-xLiNbO₃ (0 ≤ x ≤ 0.05) solid solutions are synthesized. The dielectric and acoustic properties of the solid solutions are studied in the temperature range from 15 to 300 K. It is revealed that the polar state characterized by the dispersion of the permittivity and the dielectric hysteresis occurs at low temperatures. The results obtained are discussed within the concept of relaxor ferroelectrics.     

VO2-WO3 nanocomposite thin films synthesized by pulsed laser deposition technique

Pure VO₂ and VO₂-WO₃ composite thin films were grown on quartz substrate by pulsed laser deposition (PLD) technique. The influence of varying WO₃ molar concentration in the range from x = 0.0 to x = 0.4 on structural, electrical and optical properties of VO₂-WO₃ nanocomposite thin films has been systematically investigated. X-ray diffraction studies reveal the single crystalline monoclinic VO₂ phase (m-VO₂) up to 10% of WO₃ content whereas both m-VO₂ as well as h-WO₃ (hexagonal WO₃) phases were present at higher WO₃ content (0.2 ≤ x ≤ 0.4). Optical transmittance spectra of the films showed blue shift in the absorption edge with increase in WO₃ content. Temperature dependence of resistivity (R-T) measurements indicates significant variation in metal-insulator transition temperature, width of the hysteresis, and shape of the hysteresis curve. Cyclic Voltammetry measurements were performed on VO₂-WO₃ thin films. A direct correlation between V/W ratio and structure-property relationship was established. The present investigations reveal that doping of WO₃ in VO₂ is effective to increase the optical transmittance and to reduce the semiconductor to metal phase transition temperature close to room temperature.     

Phase diagram of (1−x%)(0.89Bi0.5Na0.5TiO3–0.06BaTiO3–0.05K0.5Na0.5NbO3)–x%MnO2 lead-free anti-ferroelectric ceramics

A phase diagram for the lead-free ceramics in the (1?x%)(0.89Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.05K_0.5Na_0.5NbO₃)–x%MnO₂ (BNBKN-x%Mn) binary system is constructed for the first time based on the ferroelectric and dielectric measurements. The ferroelectric behaviors under different temperatures suggest that the ceramics are basically of relaxor anti-ferroelectric nature near room temperature. The temperature dependent dielectric properties show that when the addition of MnO₂ increases, the relaxor anti-ferroelectric phase can be stabilized to be close to the Curie point, which corresponds to a relaxor anti-ferroelectric to paraelectric phase transition.