The influence of BaGeO3 on the properties of Ba(Ti1?xSnx)O3 ceramics on the basis of sol-gel powders

Ba(Ti_1−x−y Sn _x Ge _y )O₃ (BTSG-x-y; x = 0, 0.05; y = 0–0.05) powders were synthesized by a sol-gel (SG) method and for comparative purposes also by a mixed-oxide (MO) method. In this system, BaGeO₃ functions as sintering additive. Due to smaller particle sizes of the SG powders a higher sintering activity was found, which resulted in reduced grain growth and in a more homogenous grain size distribution for the corresponding ceramics. The dependence on the paraelectric ⇆ ferroelectric phase transition, i.e. the phase transition temperature, the width of the transition region and completeness were examined by dielectric measurements, DTA as well as by SEM, EDX and XRD investigations with respect to the BaGeO₃ content, synthesis method and sintering temperature. The phase transition temperatures of the SG ceramics are remarkably higher than those of the MO ceramics with the same nominal compositions. The reason is a lower tin concentration within the grains of SG ceramics as confirmed by EDX and XRD investigations. The presence of BaGeO₃ in barium titanate–stannate system on the basis of a SG method caused an improved incorporation of tin in the BaTiO₃ lattice.     

Stabilization of the anatase phase of Ti1?xSnxO2 (x < 0.5) nanofibers

We experimentally investigate the stabilization of the anatase phase of Ti_1−x Sn _x O₂ (x < 0.5) nanofibers when synthesized by an electrospinning method. The as-spun nanofibers became nano-grained, polycrystalline nanofibers after calcination and the diameters of the nanofibers depend on Sn content. Stabilization of the anatase phase in Ti-rich compositions and incorporation of Sn ions were confirmed by X-ray diffraction, Raman, X-ray absorption near-edge structure, and photoluminescence (PL) spectroscopies. Results from the PL study also demonstrated the tunable nature of the optical properties, with the emission maximum shifting towards higher wavelength with increasing Sn concentration.      

Effect of nonstoichiometry on the structure and microwave dielectric properties of Ba1 ? x(Zn1/2W1/2)O3 ? x and Ba(Zn1/2 ? yW1/2)O3 ? y/2

We have synthesized Ba_{1 − x} (Zn_1/2W_1/2)O_{3 − x} and Ba(Zn_{1/2 − y} W_1/2)O_{3 − y/2} barium tungstates with different deviations from cation stoichiometry (x = 0.01–0.05, y = 0.01–0.05), determined the phase composition of ceramics fabricated from the tungstates, and investigated their electrical properties. Even slight deviations from cation stoichiometry in Ba(Zn_1/2W_1/2)O₃ lead to the formation of the scheelite phase BaWO₄, and its content increases with heat-treatment temperature. Barium or zinc deficiency in the systems studied improves the sintering behavior of Ba(Zn_1/2W_1/2)O₃ and increases the degree of 1: 1 B-site cation ordering, which in turn ensures an increase in microwave quality factor, Q.     

Normal state and superconductivity of ErBa2(Cu1?xCrx)O7?δ(x=0–0.1)

The effects of Cr in ErBa₂(Cu_1–x Cr _x )O_7– (x=0–0.1) superconductor have been investigated. The critical temperature, which was determined by DC electrical resistance measurements, showed no suppression of the onset temperature (T _{c onset}) within the substitution range. The transition width (T _c ) broadened as the Cr content is increased. The normal state changes from the metal-like to semimetal/semiconductor-like for x0.03. Micrographs from the scanning electron microscope, X-ray diffraction pattern, and energy dispersive X-ray analysis results are used to describe the superconducting properties of these materials. The orthorhombic structure was preserved throughout the substitution range. Some possible roles of Cr in the system are discussed.     

Structural and dielectric properties of Na1?xBaxNb1?x(Sn0.5Ti0.5)xO3 ceramics

Lead-free (1 − x)NaNbO₃/xBa(Ti_0.5Sn_0.5)O₃ (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature. As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show that the materials have a classical ferroelectric behavior for compositions in the range 0.10 ≤ x ≤ 0.15 and relaxor one for compositions in the range 0.15 < x ≤ 0.30. Temperatures T _C or T _m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d ₃₁ of 42.146 pC N⁻¹ was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.     

The morphotropic phase boundary and electrical properties of (1?? x )Pb(Zn1/2W1/2)O3– x Pb(Zr0.5Ti0.5)O3 ceramics

Ceramics in the solid solution of (1 − x)Pb(Zn_1/2W_1/2)O₃–xPb(Zr_0.5Ti_0.5)O₃ system, with x = 0.80, 0.85, 0.90, and 0.95, were synthesized with the solid-state reaction technique. The perovskite phase formation in the sintered ceramics was analyzed with X-ray diffraction. It shows that the rhombohedral and the tetragonal phases coexist in the ceramic with x = 0.90, indicating the morphotropic phase boundary (MPB) within this pseudo-binary system. Dielectric and ferroelectric properties measurements indicate that the transition temperature decreases while the remanent polarization increases with the addition of Pb(Zn_1/2W_1/2)O₃. In the composition of x = 0.85 which is close to the MPB in the rhombohedral side, a high piezoelectric property with d ₃₃ = 222 pC/N was observed.     

Structural, spectroscopic and microwave characterizations of (Sm0.5Y0.5)Ti(Nb1?xTax)O6 ceramics

Microwave dielectric ceramics of the type (Sm_0.5Y_0.5)Ti(Nb_1−x Ta _x )O₆ were prepared for x = 0, 0.2, 0.4, 0.6, 0.8 and 1 through the conventional solid state ceramic route. The ball-milled compositions were calcined at 1,250 °C. The cylindrical pellets were sintered at temperatures between 1,385 and 1,450 °C. The densities were determined by Archimedes method. The structure was analyzed using X-ray diffraction method. The microwave dielectric properties of the polished pellets were measured using cavity resonator method. The morphological studies were done using Scanning Electron Microscopy and Transmission Electron Microscopy. The Raman spectra were recorded and analyzed to confirm the structural change. The photoluminescence spectra were also taken and the emission lines were identified. A correlation study was done among the measured properties and parameters. Most of the samples have high dielectric constant, high quality factor and low temperature coefficient of resonant frequency and hence suitable for microwave applications.     

Electrical conductivity of LaCoxFe1 ? xO3 ? δ and LaLi0.1CoxFe0.9 ? xO3 ? δ (0 ≤ x ≤ 0.4) oxides

We have studied the effect of Co and Li concentrations on the phase composition and electrical conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} and LaLi_0.1Co _x Fe_{0.9 − x} O_{3 − δ} perovskite-like oxides synthesized in air at 1470 K. Single-phase materials with an orthorhombic crystal structure were obtained in the range 0 ≤ x ≤ 0.3. The composition dependences of conductivity have a minimum at x _c = 0.1 and 0.2, respectively. In the range x > 0.1, the conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} increases with increasing Co concentration for T > 700 K and decreases for T < 600 K. The conductivity of La(Li_0.1Co _x Fe_{0.9 − x} )O_{3 − δ} in the range 0 ≤ x ≤ 0.1 and for x ≥ 0.2 increases with Co concentration throughout the temperature range studied.     

Construction of new morphotropic phase boundary in 0.94(K0.4?xNa0.6BaxNb1?xZrx)O3–0.06LiSbO3 lead-free piezoelectric ceramics

0.94(K_0.4−x Na_0.6Ba _x Nb_1−x Zr _x )O₃–0.06LiSbO₃ ceramics were prepared by conventional technique, and the effect of BaZrO₃ on the phase transitions, dielectric, ferroelectric, and piezoelectric properties of the ceramics were investigated. The phase transitions for the ceramics were determined by the temperature dependence of dielectric properties and X-ray diffraction patterns. BaZrO₃ changes the symmetry of the ceramics from tetragonal dominant phase with x = 0–0.06 to rhombohedral phase with x = 0.07–0.09. The phase transition near room temperature for the composition with x ~ 0.06 is different from previously reported phase transition between orthorhombic and tetragonal phases. It is suggested that a new morphotropic phase boundary (MPB) is constructed with both rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions near room temperature, and the enhanced piezoelectric properties (d ₃₃ = 344 pC/N and k _P = 32.4% with x = 0.06) are obtained. The results indicate that the construction of new MPB is of significance for further development of KNN-based ceramics.     

X-ray photoelectron study on Ba0.5Sr0.5CoxFe1?xO3?δ (BSCF: x?=?0.2 and 0.8) ceramics annealed at different temperature and pO2

X-ray diffraction (XRD) and the X-ray photoelectron spectroscopy (XPS) were measured for the sintered BSCF ceramics (Ba_0.5Sr_0.5Co _x Fe_1−x O_3−δ, x = 0.2 and 0.8: BSCF5528 and BSCF5582, respectively), which were annealed at different temperatures (700 and 950 °C) and gases (O₂ and Ar). The unit cell of the annealed BSCF5528 at 950 °C under Ar expanded by 0.8%, while contracting by 0.45% under O₂. The cubic and rhombohedral phases coexist in the BSCF5582 annealed at 700 °C under O₂. The XPS peak areas of lattice oxygen (O²⁻) in O_1s , ~528 eV, and the shoulder peak of Co_2p /Ba_3d in BSCF5582 (~778 eV) increased significantly after being annealed in O₂. The areas of the peaks for BaCO₃ (87.9/90.2 eV) in Ba_4d preferentially were shown to decrease in Ar and increase in O₂.     

Dielectric and piezoelectric properties of (1 ? 2x)BiScO3 · xPbTiO3 · xPbMg1/3Nb2/3O3 (0.30 ≤ x ≤0.46) solid solutions

We have synthesized ceramic samples of (1 − 2x)BiScO₃ · xPbTiO₃ · xPbMg_1/3Nb_2/3O₃ perovskite solid solutions with 0.30 ≤ x ≤ 0.46 and studied their structural, dielectric, and piezoelectric properties. At x = 0.40, the system has a morphotropic phase boundary between tetragonal (x > 0.40) and rhombohedral (x < 0.40) solid solutions. The dielectric permittivity and loss tangent of the solid solutions have been measured at temperatures from 100 to 800 K and frequencies from 0.1 to 200 kHz. The maximum in the permittivity of the solid solutions lies in the range 390–440 K. With increasing BiScO₃ content, features characteristic of fer-roelectric relaxors emerge and become more pronounced. Near the morphotropic phase boundary, the piezoelectric charge coefficients d ₃₃ and d ₃₁ of the solid solutions reach 410 and 150 pC/N, respectively, and their radial-mode mechanical Q drops to 22, which makes these materials potential candidates for a number of applications.     

Dielectric Characteristics and Orientation of Piezoelectric (PbZrxTi1?xO3, PZT) Films Fabricated by Sol-Gel Spray and?Spin Techniques

The paper presents PbZr _x Ti_1−x O₃ (PZT) thick/thin films fabricated by spray and spin coating technologies. The PZT sol-gel is prepared by mixing PZT powder and PZT solution, and fabricated on the aluminum and nickel substrates for several layers. After drying, firing and annealing, the films were polarized by the corona poling technique. The average thicknesses of fabricated films were 3 and 10 μm for spin and spray coating techniques, respectively. The dielectric characteristics and orientation of films had been measured by LCR meter, XRD for comparison. The crystallization of the PZT structure fabricated by a spin coating technique was denser than that by a spray coating technique, especially for thicker layers. The dielectric constant increased with coating layers, and the dissipation factor decreased with coating layers. The films fabricated by a spray coating technique had better performance on these two parameters than those by the spin coating one.     

Production and dielectric properties of lead-free ceramics with the formula [(Na0.5K0.5)1 ? xLix](Nb1 ? y ? zTaySbz)O3

The influence of past history on the possibility of obtaining high-density ferroelectric ceramics of solid solutions [(Na_0.5K_0.5)_{1 − x} Li _x ](Nb_{1 − y − z} Ta _y Sb _z )O at x = 0–0.14, y = 0, 0.1, 0.2, and z = 0–0.1 is identified. The dynamics of behavior of materials under a field in the process of polarization is evaluated. The relative dielectric permeability of samples in a wide range of temperatures (20–700°C) and frequencies (25 Hz-1 MHz) of a variable electric field is studied. On the basis of study of dielectric, piezoelectric, and elastic properties of solid solutions, prospective objects for further technological elaboration and modification of chemical composition with the goal of improving the electrophysical parameters are selected. Original Russian Text ? I.A. Verbenko, O.N. Razumovskaya, L.A. Shilkina, L.A. Reznichenko, K.P. Andryushin, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 6, pp. 762–768.     

Structure of Sr1 ? xPbxFeO3 ? δ (0 < x < 0.5) perovskite-like materials

We have synthesized Sr_{1 − x} Pb _x FeO_{3 − δ} (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5) perovskite-like materials and studied their structure by X-ray diffraction, M?ssbauer spectroscopy, and electron microscopy. According to the X-ray diffraction data, the Pb solubility limit in the perovskite structure is x ≈ 0.15. The materials with x = 0.05 and 0.1 contained Pb_1.33Sr_0.67Fe₂O₅ inclusions 10–30 nm in size. Using chronopotentiometry and temperature-programmed desorption, we have estimated oxygen mobility in the materials with x = 0.05 and 0.1. The results demonstrate that Pb doping increases oxygen mobility in the strontium-ferrite-based materials.     

Microwave properties of the systems Ba1?xSrx(Zn1/3Ta2/3)0.94T{i}0.06 O3 and Ba(Zn1/3Nb2/3)1?xZrxO3

By means of a solid-phase synthesis two types of microwave dielectric materials are obtained as follows: Ba_1–xSr_x(Zn_1/3Ta_2/3)_0.94Ti_0.06O₃, where x = 0.20, 0.25, 0.30, 0.35 and 0.40 at sintering temperature T_S = 1350, 1400 and 1450 C; Ba(Zn_1/3Nb_2/3)_1–xZr_xO₃, where x = 0.04, 0.06, 0.08 and 0.10 at T_S = 1300, 1350, and 1400 C. The microwave characteristics of the materials are investigated at f = 10 GHz. The composition Ba(Zn_1/3Nb_2/3)_1–xZr_xO₃ demonstrates _r = 38, Q = 6100 and _f = +15 ppm C^–1 and the composition Ba_0.80Sr_0.20- (Zn_1/3Ta_2/3)_0.94Ti_0.06O₃ has _r = 42, Q = 8200 and _f = –13 ppm C^–1. The composition Ba_0.75Sr_0.25(Zn_1/3Ta_2/3)_0.94Ti_0.06O₃ has _r = 40, Q = 6500 and low _f = –13 C^–1 ppm. This composition could be used successfully for realisation of dielectric microwave resonators for the satellite television.     

Synthesis and magnetic properties of nanocrystalline Y1 ? xCdxFeO3 ? δ (0 ≤ x ≤ 0.2)

We report the synthesis of Y_{1 − x} Cd _x FeO_{3 − δ} nanocrystals in the range x = 0–0.2. The Y_{1 − x} Cd _x FeO_{3 − δ} materials were shown to be single-phase by X-ray diffraction, with an average crystallite size from 23 to 34 nm, depending on composition. With increasing cadmium oxide content, the size of the Y_{1 − x} Cd _x FeO_{3 − δ} nanocrystals decreases and their magnetization rises.     

Superconducting Properties of Carbon and Zn Double-doped Mg1?xZnx(B1?xCx)2

A series of polycrystalline samples of Mg_1−x Zn _x (B_1−x C _x )₂ (x=0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) were synthesized by a conventional solid-state reaction method under a background pressure about 10⁻³ Pa. Phase identification, crystal structure and superconducting transition temperature (T _c) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicated that the lattice parameters a and c show no clear trend in their changes with increasing doping level, and it turned out that the dopants had a marked effect on the crystal-lattice parameters and changed the crystal structure of the samples. The T _c for Mg_1−x Zn _x (B_1−x C _x )₂ decreased with C and Zn doping, but the rate of decrease was slower than single C-doped. We propose that the suppression of T _c by doping originates largely from the structural change.     

Synthesis and characterization of Al2?xScx(WO4)3 ceramics for low-expansion infrared-transmitting windows

A low thermal-expansion material was synthesized with potential application in thermal-shock-resistant infrared-transmitting windows. The material is derived from a solid solution of Al₂(WO₄)₃, which has positive thermal expansion, and Sc₂(WO₄)₃ with a negative thermal expansion. An optimum composition of Al_0.5Sc_1.5(WO₄)₃ was identified by synthesizing solid solutions, Al_2−x Sc _x (WO₄)₃, by a solid-state route with compositions ranging from x = 0 to 2.0. A single orthorhombic phase was obtained at all compositions. A composition corresponding to x = 1.5 had a low coefficient of thermal expansion of −0.15 × 10⁻⁶/°C in the temperature range 25–700 °C. A low temperature solution combustion process was developed for this optimum composition, resulting in a single-phase powder with a surface area of ~14 m²/g and average particle size (as determined from surface area) of 92 nm. The powder was consolidated by slip-casting, sintering, and hot-isostatic pressing into visibly translucent disks with a peak in-line transmittance of 73 % at 2300 cm⁻¹. Significant infrared absorption in a 1-mm-thick disk of this material begins near 2200 cm⁻¹ and features three absorptions arising from 2-phonon transitions at 2002, 1847, and 1676 cm⁻¹. The infrared and Raman spectra are interpreted in terms of 1-, 2-, and 3-phonon vibrational transitions.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.