Crystal structure and dielectric properties of (Pb1−x Ca x )(Zr1−y Sn y )O3 ceramics

There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO₃ ceramics have a dielectric constant (_r), high quality factor (Q) and a small temperature coefficient of resonant frequency (_f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb_1–x Ca _x )(Zn₁– _y Sn _y )O₃ ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data.     

Effect of silver addition on superconductivity in the Bi1.6Pb0.4Sr1.6Ca2Cu3O10−y system

Silver/superconductor composites containing 0 to 80 vol% silver have been prepared and their properties determined. Optimum heat treatment at sintering temperatures ( 800° C) under low oxygen pressures produces material with high critical current density and improves physical properties. Magnetic susceptibility measurements have been found to be consistent with resistivity results. In order to retain a single high-T _c phase with increasing silver content, decreased oxygen partial pressures are required. Using the normal-state resistivity of these composites, a percolation threshold at a silver volume fraction of 43% was observed, while zero resistivity measurements show that a continuous superconducting network can be obtained with up to 80 vol% silver. The critical current density of 21 vol% silver-doped samples was found to be 1520 A cm^–2 at 77.3 K, compared to 260 A cm^–2 for an undoped sample.     

High dielectric tunability of ferroelectric (Ba1−x,Srx)(Zr0.1,Ti0.9)O3 ceramics

(Ba_1?x,Sr_x)(Zr_0.1,Ti_0.9)O₃ (BSZT) ceramics with x = 0, 0.05, 0.15, 0.25, 0.35 and 0.45 were prepared by conventional solid state reaction method. The structural characterization with X-ray diffraction and scanning electron microscopy indicate a monotonical drop in lattice constants and grain size with the increase of Sr concentration. Consequently, the Curie temperature and remnant polarization of the ceramics exhibit a strong compositional dependence. A linear relationship between the Curie temperature and Sr concentration is revealed. At x = 0.45, the BSZT ceramics show substantially high tunability of over 55 % under 20 kV/cm dc electric field with very low dielectric loss value of 0.0025 at room temperature, suggesting the BSZT ceramics could be a promising alternative to traditional (Ba,Sr) TiO₃ ferroelectrics for developing high frequency tunable dielectric devices.     

Microwave dielectric properties of (Ca0.8Sr0.2)(SnxTi1−x)O3 ceramics

In this paper, we study the behavior of the B-site behavior with the incorporation of Sn⁴⁺ ion in (Ca_0.8Sr_0.2)TiO₃ ceramics. An excess of Sn⁴⁺ resulted in the formation of a secondary phase of CaSnO₃ and SrSnO₃ affecting the microwave dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics. The dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics were improved because of the solid solution of Sn⁴⁺ substitution in the B-site. The temperature coefficient of resonant frequency (τ_f) of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics also improved with increasing Sn content.     

Crystalline structure and dielectric properties of Ba(Ti1−y Ce y )O3

Crystalline structure, microstructure and dielectric properties for Ba(Ti_1–y Ce _y )O₃ (0 y 0.5) ceramics have been studied. Dense ceramics with the relative density higher than 95% and grain size of 0.7–1.5 m have been obtained. The limit of the solid solubility is determined as y = 0.3 by the X-ray diffraction, SEM, and dielectric properties measurements. The crystalline symmetry is tetragonal for the sample with y = 0.02 and cubic for y 0.06 at room temperature, and the unit cell increases with increasing Ce content in the solid solution range. Correspondingly, the dielectric response exhibits three dielectric peaks for y = 0.02, and one pinched dielectric peak with ferroelectric relaxor behavior for y 0.06.     

Electric-field effect on phase transitions in Pb0.995La0.005[Zr0.9 − y Sn0.1Ti y ]0.99875O3 and Pb0.9975[Zr0.895 − y Sn0.1Ti y Nb0.005]O3 solid solutions

The phase diagrams of PbZrO₃-PbTiO₃-PbSnO₃ solid solutions doped with $ La_{Pb^{2 + } }^{3 + } The phase diagrams of PbZrO₃-PbTiO₃-PbSnO₃ solid solutions doped with and have been constructed using the temperature dependences of their linear dimensions and relative dielectric permittivity measured during zero-field cooling and field cooling. Doping to a level as low as 0.5 at % has a significant effect on the temperature and electric field at which the tetragonal antiferroelectric phase forms. Field cooling of the antiferroelectric solid solutions close in composition to the morphotropic phase boundary consecutively stabilizes two ferroelectric phases. The ferroelectric state produced by field cooling is often inhomogeneously poled and has an asymmetric dielectric hysteresis loop. Original Russian Text ? E.A. Bikyashev, E.A. Reshetnikova, I.V. Lisnevskaya, T.G. Lupeiko, M.I. Tolstunov, 2009, published in Neorganicheskie Materialy, 2009, vol. 45, No. 5, pp. 606–611.     

Effect of microstructure on oxygen permeation in SrCo0.8Fe0.2O3−δ

The effect of microstructure on oxygen permeation in SrCo0.8Fe0.2O3– membranes was investigated using disc samples fabricated under different processing conditions of applied pressure and sintering temperature. The average grain size of the samples was found to remain unchanged as a function of applied pressure, but increased considerably when the sintering temperature was increased from 950 to 1200°C. This change in grain size has a strong effect on the oxygen permeation flux, which increased considerably as the grain size was decreased. The density as well as the microhardness of these samples were also measured and found to change slightly as the processing conditions were changed.     

Synthesis,structural and dielectric properties of 0.8PMN–0.2PT relaxor ferroelectric ceramic

A 0.8PMN–0.2PT solid-solution ceramic was synthesized by columbite processing technique. The effects of sintering temperature on the density, structure and microstructure and in turn on the dielectric properties were investigated. The ceramics sintered at and above 1050\(^{\circ }\hbox {C}\) resulted in single-phase perovskite formation. However, high density >90% is achieved only after 1170\(^{\circ }\hbox {C}\). Microstructural analysis revealed that grain size increases with increase in sintering temperature. A significant increase in the peak of dielectric permittivity only after 1150\(^{\circ }\hbox {C}\) owing to increase in density is noted in this study. The quadratic law applied to this ceramic demonstrates that the transition is diffused. The broadness in phase transition and lower dielectric relaxation obtained for the composition demonstrate that the ceramic exhibits characteristics of both relaxor and normal ferroelectrics. The ceramic of composition 0.8PMN–0.2PT exhibits excellent dielectric properties \(\varepsilon _{\mathrm{r}\text {-}\mathrm{max}} =\) 20294?27338 at 100 Hz with \(T_{\mathrm{c}} = 100\)–\(96^{\circ }\hbox {C}\) at low sintering temperature 1170–1180\(^{\circ }\hbox {C}\), respectively.     

Preparation,structure and dielectric properties of the system Sr1−xLaxTi1−xNixO3

Attempts have been made to synthesize the solid solution Sr_1–x La _x Ti_1–x Ni _x O₃ for x0.50 and its electrical behaviour has been studied. It was found that a solid solution forms for compositions up to x=0.10. The structure remained cubic. These compositions exhibited dielectric relaxator behaviour. The average grain size in these materials was very small.     

Nonstoichiometry and physical properties of the perovskite BaxLa1−xFeO3−y system

A series of samples in the Ba _x La_1–x FeO_3–y system (x=0.00, 0.25, 0.50, 0.75, and 1.00) have been prepared at 1200°C under an atmospheric air pressure. The solid solutions of the system were analysed from the X-ray diffraction spectra and thermal analyses. X-ray diffraction studies assigned the compositions of the x=0.00 and 1.00 to the orthorhombic system and the compositions of the x=0.25, 0.50, and 0.75 to the cubic system. The reduced lattice volume increased with the x value in the system. The mole ratios of the Fe⁴⁺ ion in the solid solutions, or values, were determined by Mohr salt analyses and the non-stoichiometric chemical formulae of the system were formulated from the x, , and y values. From the results of the Mössbauer spectroscopy, the coordination and the magnetic property of the iron ion have been discussed. The electrical conductivities were measured as a function of temperature under atmospheric air pressure. The activation energy was minimum at the composition of x=0.50. The conduction mechanism can be explained by the hopping model between the mixed valences of the Fe³⁺ and Fe⁴⁺ ions.     

The nonstoichiometry and physical properties of the Nd1−x Ca1+x FeO4−y system

The solid solutions of the Nd_1–x Ca_1+x FeO_4–y system for compositions ofx=0.000,0.125, 0.250,0.375, and 0.500 are prepared by drip pyrolysis. XRD analysis shows all the solid solutions are tetragonal I_4/mmm. The Fe⁴⁺ ratio to the total Fe ions or value has a maximum for the compositionx=0.375. From the X-ray powder diffraction analysis and the Mössbauer spectroscopy, the distortion and symmetry change of oxygen octahedra of Fe ions are observed. The structural change of oxygen octahedra of Fe ions strongly affects the physical properties. The solid solution whenx=0.000 shows a weak ferromagnetic behaviour due to the spin canting of the distorted octahedra. The other solid solutions withx=0.125, 0.250, 0.375, and 0.500 show a paramagnetic behaviour over room temperature. The decrease of the magnetic transition temperature is due to the distortion of oxygen octahedra of Fe ions and the existence of the Fe⁴⁺ ion. The formation site of oxygen vacancies plays an important role in the conductivity of the Nd_1–x Ca_1+x FeO_4–y system. Although the oxygen vacancies in [Nd, Ca]-O layer have little effect on conductivity, the oxygen vacancies in the FeO₂ plane of the perovskite layer act as electron trapping sites and thus increase the activation energy.     

High temperature thermoelectric properties of the Ca3−xBxCo4O9 system

The Ca_3?xB_xCo₄O₉ system (x = 0.0, 0.05, 0.75 and 1.0) has been prepared using the solid-state reaction technique. Structural, microstructural, transport properties (temperature dependence of resistivity, thermoelectric power) of the samples fabricated were investigated in details. The structural/microstructural investigations showed that complex and multiphase crystallographic structure was formed with the B-substitution. A decrease in the grain size was observed in the B-substituted samples. The resistivity increased with the substitution due to decrease in the grain size and weak-link among the grains. It is found that that the thermoelectric power is insensitive to the B-substitution. The highest power factor value was obtained in the x = 0.0 sample, however, it decreased in the B-substituted samples.     

Dielectric and magnetoelectric properties of (Ni,Cu)Fe2O4 + [(Ba,Pb)(Ti,Zr)]O3 composites

The observation of magnetoelectric coupling is reported in (x) Ni_0.8Cu_0.2Fe₂O₄ + (1 − x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ composites synthesized by normal solid state reaction method. The phase formation was confirmed by X-ray diffraction technique and no intermediate or impurity phase is present in all the composites. The dielectric constant (ε′) and dielectric loss (tan δ) were measured as a function of frequency and temperature. The dielectric constant was found to be enhanced with increase in ferrite content in the composite. It was also revealed that magnetoelectric output decreases with increase in ferrite content in the composite due to leakage current. The maximum voltage coefficient of 0.411 mV/cm/Oe was observed in 15% Ni_0.8Cu_0.2Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ composite.     

Effect of mechanical pressure and sintering temperature on the electrical properties of the rare earth ferrite Li0.6Co0.1Dy x Fe2.3−x O4; 0.0 ≤ x ≤ 0.2

Polycrystalline samples of mixed ferrite Li_0.6Co_0.1Dy _x Fe_2.3–x O₄; 0.0 x 0.2 were prepared by the standard ceramic technique. X-ray diffraction analysis was carried out to assure the formation of the samples. The resistance was measured at different temperatures (300–800 K) as a function of frequency (200 kHz–5 MHz) for the investigated samples prepared at different sintering temperatures (1100°C T _s 1250°C). It is found that this type of rare earth ferrite gives a distinguishable behavior at T _s = 1200°C where the resistance of the samples at room temperature reduced to 90% of their values of the others sintering temperatures. The data showed also that the resistance of these samples sintered at 1100°C is changed at 100 kHz from 12 M without applying pressure to 19 k with 0.8 MPa. This change occurs in a reversible manner (i.e., after removing the mechanical pressure effect the resistance of the samples well return to their initial values again immediately). Thus this type of rare earth ferrite could be more applicable in several advanced electronic devices can be used as a sensor for the mechanical pressure.