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.     

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.     

Lattice parameters and dielectric properties of (1 ? x)Bi(Mg1/2Ti1/2)O3 · xBiCoO3 perovskite solid solutions

(1 − x)Bi(Mg_1/2Ti_1/2)O₃ · xBiCoO ceramics have been prepared at high pressures (6 GPa) and temperatures (1370–1570 K). Perovskite solid solutions have been obtained in the composition ranges 0 < x < 0.6 and 0.8 < x < 1. The Bi(Mg_1/2Ti_1/2)O₃-based perovskite phase (x < 0.6) has an orthorhombic structure (sp. gr. Pnnm), which persists up to the decomposition temperature of the material. The BiCoO₃-based phase (x > 0.8) has a tetragonal structure (sp. gr. P4mn). In the range 0.6 < x < 0.8, the ceramics consisted of the two perovskite phases. The lattice parameters of the solid solutions with x < 0.6 are linear functions of composition. The dielectric properties of the orthorhombic solid solutions have been studied using impedance spectroscopy. The temperature dependences of dielectric permittivity ɛ′ and dielectric loss tanδ exhibit different behaviors at low and high temperatures. With increasing x, the boundary between these regions shifts from about 450 to 300 K. At high temperatures, both ɛ′ and tanδ rise steeply. The dc conductivity of the solid solutions with x < 0.6 exhibits Arrhenius behavior. The activation energies for charge transport in the ceramics studies are presented.     

Magnetic and dielectric properties of Mg1+x Mnx, Fe2?2x, O4 ferrite system

Ferrites with the general formula Mg_1+xMn_xFe_2–2xO₄(where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared by the standard ceramic technique and studied by means of X-ray diffraction, magnetization, a.c. susceptibility and dielectric constant measurements. The X-ray analysis confirmed the single-phase formation of the samples. The lattice parameter is found to increase up to x = 0.3 and thereafter it decreases as x increases. The cation distribution has been studied by X-ray analysis and magnetization. Magnetization results exhibit collinear ferrimagnetic structure for x 0.3 and thereafter structure changes into non-collinear for x > 0.3. Curie temperature (T_C) obtained from a.c. susceptibility data decreases with increasing x. The dielectric constant (), loss tangent (tan ) show strong frequency dependence.     

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.     

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.     

Frequency effect on the electrical and dielectric properties of (TlGaS2) 1 ? x(TlInSe2)x (x = 0.005, 0.02) single crystals

The electrical properties (loss tangent (tanδ), real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity, and ac conductivity across the layers (σ_ac)) of (TlGaS₂)_{1 − x} (TlInSe₂) _x (x = 0.005, 0.02) layered single crystals have been studied in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. Almost throughout the frequency range studied, their ac conductivity follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states (N _F ), the spread of their energies, the mean hop time τ and distance R, and the concentration of deep traps determining the ac conductivity of the crystals (N _t ) have been estimated. With increasing x in (TlGaS₂)_{1 − x} (TlInSe₂) _x , N _F and N _t increase, while τ and R decrease.     

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.     

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.     

Dielectric Ba(Ti1?xSnx)O3 (x?=?0.13) ceramics, sintered by spark plasma and conventional methods

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti_0.87Sn_0.13)O₃ ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti_0.87Sn_0.13)O₃ ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were ~92% of the theoretical value of Ba(Ti_0.87Sn_0.13)O₃. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature of 63 °C and 10 Hz.     

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.     

Electrical properties of Zn2(TiaSnb)1 ? xZrxO4 solid solutions

The electrical conductivity, band gap, dielectric permittivity, and molar polarizability of Zn₂(Ti _a Sn _b )_{1 − x} Zr _x O₄ solid solutions have been determined. All of the synthesized samples are dielectrics with semiconducting behavior of conductivity. The phase diagram of the Zn₂TiO₄-Zn₂SnO₄-Zn₂ZrO₄ system is presented.     

Self-propagating combustion synthesis of Pb1?xSrxZrO3 (0 ≤ x ≤ 0·20) ceramics and their dielectric properties

Lead strontium zirconate, Pb_1−x Sr _x ZrO₃ (0 ≤ x ≤ 0·20) ceramics, were prepared by novel glycinenitrate self-propagating combustion technique. The crystal structure of the ceramics was investigated as a function of composition via X-ray diffraction (XRD). The XRD patterns obtained on these powders showed the formation of pure orthorhombic phase of lead strontium zirconate without impurities and all the compounds retained the orthorhombic structure. The samples were sintered at 900–1100°C for 2 h. It has been observed that the dielectric constant decreases with increase in strontium content (100 kHz). In all compositions, dielectric constant showed a peak at transition temperature and the magnitude of the peak was found to decrease with strontium doping level.     

Electrical properties and microstructure of CdxHg1 ? x ? yCrySe crystals

Crystals of the Cd _x Hg_{1 − x − y} Cr _y Se (x = 0.4, y = 0.1) quaternary solid solution have been grown by the Bridgman method, and their microstructure and electrical properties have been studied. The crystals are shown to contain various types of inclusions in the form of filaments and triangles.     

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.     

Magnetic susceptibility of (Bi2 ? xSbx)Te3 (0 < x < 1) crystals from 2 to 400 K

The magnetic susceptibility (χ) of crystals of (Bi_{2 − x} Sb _x )Te₃ (0 < x < 1) solid solutions has been measured at temperatures from 2 to 400 K. The χ of the crystals containing 10 and 25 mol % Sb₂Te₃ increases with temperature in the range 50 to 220 K, where the Hall coefficient of Bi₂Te₃ increases anomalously. The increase in diamagnetic susceptibility and Hall coefficient with temperature is shown to be caused by a reduction in light-hole concentration, accompanied by a decrease in light-hole effective mass. With increasing Sb₂Te₃ content, the shape of the χ(T) curve changes as a consequence of changes in band structure, which increase the influence of heavy, paramagnetic holes.     

X-ray diffraction study of multicomponent oxides in the Zn2 ? x(TiaZrb)1 ? xFe2xO4 system

The multicomponent refractory oxide system Zn_{2 − x} (Ti _a Zr _b )_{1 − x} Fe_2x O₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1, 4: 1; x = 0–1.0; Δx = 0.05) has been studied by X-ray diffraction, using samples prepared by melting appropriate metal oxide mixtures in a low-temperature hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse spinel structure, and β-phase, with a tetragonal inverse spinel structure. The phase boundaries in the system have been determined. Structural data are presented for about 100 solid solutions.     

Synthesis and abrasive properties of nanoparticulate MoO2-modified Al2 ? xFexO3 and Fe2 ? yAlyO3 solid solutions

X-ray diffraction, IR spectroscopy, particle-size analysis, and chemical analysis are used to elucidate the general mechanisms of the formation of nanoparticulate molybdenum-dioxide-modified Al_{2 − x} Fe _x O₃ and Fe_{2 − y} Al _y O₃ solid solutions prepared via heat treatment of ammonium hydroxycarbonate complexes, (NH₄)₂Al₂Fe(OH)₅(CO₃) · nH₂O. The addition of molybdenum dioxide (within 0.005 mol %) is shown to enhance the polishing performance of the oxides for final polishing of nonferrous metals and alloys (copper and brass) by a factor of 6–7 relative to unmodified aluminum iron oxides, which is attributable to the increased chemical activity of the abrasive material. The surface roughness value R _a achieved is below 0.005 μm.     

Temperature dependence of dielectric and piezoelectric properties of (1?x)(BiScO3–0.64PbTiO3)–xLiNbO3 high-temperature relaxor ferroelectric ceramics

(1−x)(0.36BiScO₃–0.64PbTiO₃)–xLiNbO₃ (BSPT64–xLN) high-temperature relaxor ferroelectric ceramics near the morphotropic phase boundary (MPB) composition were investigated. X-ray diffraction showed a change in symmetry from MPB phase to rhombohedral phase with LiNbO₃ content increasing. A change from normal ferroelectric features to relaxor ferroelectric features was observed with LiNbO₃ substitution up to x = 0.06, while high-temperature dielectric relaxation was exhibited at T _max ~230 to 383°C for 0.02 ≤ x ≤ 0.06. The BSPT64–xLN ceramics with x = 0.02 LiNbO₃ exhibited good piezoelectric properties compared with BS–0.64PT ceramics: piezoelectric coefficients d ₃₃ = 505pC/N, planar electromechanical coupling factors k _p = 0.47, and remnant polarization P _r = 40 μC/cm², respectively. The annealing temperature dependence of piezoelectric response for BSPT64–xLN ceramics was measured and it was found that the piezoelectric properties decreased slightly before 210°C for x = 0.02 and 0.04, showing excellent thermal stability, which indicated that BSPT64–xLN relaxor ferroelectric ceramics can be used in the range of high temperature compared to Pb-based relaxor ferroelectrics.     

Electrical conductivity and thermal stability of (1 ? x )CsH2PO4/ x SiP y O z ( x = 0.2–0.7) composites

The physicochemical properties of (1 − x)CsH₂PO₄/xSiP _y O _z (x = 0.2–0.7) composites containing fine-particle silicon phosphates as heterogeneous additives have been studied at different humidities. The introduction of silicon phosphates suppresses the superionic phase transition of CsH₂PO₄ and increases the low-temperature conductivity of the materials, which depends significantly on humidity. The CsH₂PO₄-SiP _y O _z materials offer high conductivity (∼3 × 10⁻³ to 10⁻² S/cm at ∼110–230°C) at low water vapor pressures (3 mol % H₂O). Amorphization of the CsH₂PO₄ in the composites markedly changes its thermodynamic properties. The effect of long-term isothermal holding (210°C, 3 mol % H₂O) on the conductivity of the composites has been studied. Original Russian Text ? V.G. Ponomareva, E.S. Shutova, G.V. Lavrova, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 9, pp. 1131–1136.