Formation of the La0.03Sr0.255Ba0.7Nb2–yTiyO6–y/2 ferroelectric ceramic system

The study of the formation of the Sr_0.255La_0.03Ba_0.7Nb_{2 – y} Ti _y O_{6 – y/2} ferroelectric ceramic system and the influence of the sintering conditions and titanium concentration on the densification process is reported. A single-phase compound is observed for low titanium content (y 0.1) in the XRD spectra, being isostructural with the tetragonal tungsten bronze SBN phase. For high titanium concentrations (y > 0.1) the XRD patterns show, besides the tetragonal phase reflections, several small peaks evidencing an additional phase in the compound. This second phase was identified as isostructural to hexagonal Ba₆Nb₉Ti₇O₄₂. The grain size shows a linear increase with titanium content in the region of monophasic compositions and a possible liquid phase aided sintering process is analyzed.     

Dielectric and pyroelectric properties of monovalent-lithium modified trivalent-samarium doped barium strontium sodium niobate tungsten bronze structured ceramics

The dielectric and pyroelectric properties of trivalent-samarium doped barium strontium sodium niobate tungsten bronze structured ceramics are further modified with monovalent-Lithium. Ba_1.6−(3/2)y Sr_2.4Sm _y Li _x Na_(2−x)Nb₁₀O₃₀ was studied for y = 0.1 and x in the range of 0 ≤ x ≤ 1. The BSSLNN ceramics can be indexed by typical orthorhombic structure and these orthorhombic (mm2) peaks are assigned to standard file No. C73-1214. Tolerance factor and average electronegativity difference has been determined for BSSLNN ceramics. Pyroelectric and DC resistivity properties of BSSLNN ceramics are reported. x = 1 composition was found to be optimum among the series for possible pyroelectric applications.     

Densification and phase formation in seeded, reactively sintered Sr0.53Ba0.47Nb2O6 ceramics

Sr_0.53Ba_0.47Nb₂O₆ (SBN53) ceramics were reactively sintered from SrNb₂O₆ and BaNb₂O₆ powders. The formation temperature decreased from 1260°C for unseeded samples to 1130°C for the samples with 15.4 wt% seeds plus 0.85 mol% V₂O₅ at a heating rate of 4°C/min. For the V₂O₅-free samples, the activation energy was lowered from 554 ± 15 kJ/mol for unseeded samples to 241 ± 17 kJ/mol for the samples with 15.4 wt% seeds. In the V₂O₅-containing samples, densification and phase formation occurred simultaneously. In the V₂O₅-free samples, however, phase formation was completed before densification. In both cases, ceramics with 95% relative density were obtained. In all cases, SBN53 formed directly, rather than via a variety of intermediate SBN solid solutions. The microstructure evolution was also studied.     

Microstructure and dielectric properties of CBS glass-doped Sr0.5Ba0.5Nb2O6 ceramic system

40CaO–20B₂O₃–40SiO₂ (abbreviate as CBS) glass-doped Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO₃. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric constant of the samples at the Curie temperature (T _c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase are found to obviously increase with increase in CBS glass doping level.     

Low temperature preparation of nanocrystalline Sr0.5Ba0.5Nb2O6 powders using an aqueous organic gel route

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramic powders have been synthesized by an aqueous organic gel route. Homogeneous Sr-Ba-Nb precursor gels are prepared with Ba-EDTA, Sr-EDTA, and Nb-citrate complex as source of Sr, Ba, and Nb, respectively. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used as the chelating agents. The structural variation of the SBN powder with annealing temperature was studied by TG-DTA, FT-IR and XRD. The precursor gel on calcination at 800 °C for 2 h produces a pure tungsten bronze SBN phase and the corresponding average particle size is 30-50 nm. The influences of the pH and the molar ratio of citric acid:Nb cation on the formation of homogeneous Sr-Ba-Nb precursor gels were also studied. The results show that a homogeneous Sr-Ba-Nb precursor gel with no precipitate is formed at pH 8 and the optimum molar ratio of citric acid and the metal cations is 3:1.     

Structure and microwave dielectric properties of Ba3Ti4−x (Fe1/2Nb1/2) x Nb4O21 solid solutions

Ba₃Ti_4−x (Fe_1/2Nb_1/2) _x Nb₄O₂₁ (0 ≤ x ≤ 4) ceramics with the substitution of (Fe_1/2Nb_1/2) for Ti were investigated. The modified Ba₃Ti₄Nb₄O₂₁ dielectric ceramics prepared via the solid state reaction route exhibited single hexagonal structure. The dielectric constant and the quality factor of Ba₃Ti_4−x (Fe_1/2Nb_1/2) _x Nb₄O₂₁ (0 ≤ x ≤ 4) ceramics decreased with an increase of x. Improved temperature coefficient of the resonant frequency of samples was obtained by the substitution of (Fe_1/2Nb_1/2) for Ti. Optimal microwave dielectric properties of ε _r = 50, Q × f = 5200 GHz, and τ _f = 10 ppm/°C in Ba₃Ti₂(Fe_1/2Nb_1/2)₂Nb₄O₂₁ were obtained, which indicated its potential for microwave application.     

Effect of vanadium doping on sintering and dielectric properties of strontium barium niobate ceramics

Strontium barium niobate, Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics doping up to 3 wt% V₂O₅ were fabricated by solid state reaction route, starting from raw materials (oxides and carbonates) of analytical grade. The phase composition, microstructure and dielectric properties were investigated by X-ray diffraction, scanning electric microscope and impedance analyzer. The results show that the addition of V₂O₅ improves sintering densification of SBN ceramic samples. The relative density of the samples firstly increases and then slightly decreases with increasing amounts of V₂O₅ and sintering temperature. With the help of the additive of 1 wt% V₂O₅, the relative density of the sample sintered at 1,280 °C for 3 h can reached 97.2%. Only single tetragonal tungsten bronze phase SBN exists in all the doped samples. With increase in V₂O₅ content, the dielectric constant of SBN ceramics at both room temperature and in the vicinity of the phase transition temperature increases significantly and the Curie temperatures (Tc) obviously shifts to low temperature as well as the dielectric loss remains below 0.06. The diffuseness in the phase transition is found to increase with increase in vanadium doping level. The addition of V₂O₅ results in an increased grain size associated with rod-like grain growth.     

Low temperature preparation of nanocrystalline solid solution of strontium barium niobate by chemical process

Sr_xBa_1-xNb₂O₆ (with x = 0.4, 0.5 and 0.6) powders have been prepared by thermolysis of aqueous precursor solutions consisting of triethanolamine (TEA), niobium tartarate and, EDTA complexes of strontium and barium ions. Complete evaporation of the precursor solution by heating at ∼ 200°C, yields in a fluffy, mesoporous carbon rich precursor material, which on calcination at 750°C/2 h has resulted in the pure SBN powders. The crystallite and average particle sizes are found to be around 15 nm and 20 nm, respectively.     

Influence of Ce3+ on dielectric properties of tungsten bronze structured PBN ceramics

The effect of A-site substitution of Ce³⁺ in tungsten bronze structured PBN ceramics with the general formula, Pb_{(x − 3y/2)}Ce _y Ba_(1 − x)Nb₂O₆ and the stoichiometric chemical formula, Pb_{(0.65 − 3y/2)}Ce _y Ba_0.35Nb₂O₆, where y = 0, 2, 4, 6, 8 and 10 mol% ceramic compositions synthesized through solid state reaction method are reported. The X-ray diffraction studies exhibited the presence of an orthorhombic phase, and its intensity increased with the increasing Ce³⁺ content up to y = 6 mol% or A₃ composition. The lattice parameters, unit cell volume and density as a function of Ce³⁺ concentration are discussed. It is observed that increasing Ce³⁺ content in A-site influenced the dielectric properties. The optimum dielectric properties of room temperature dielectric constant (ε_RT) and dielectric maximum () are observed in y = 6 mol% or A₃ composition while Curie temperature (T _c) and dielectric loss (tan δ) constantly decreased from undoped to y = 10 mol%, and thus A₃ composition or 6 mol% Ce modified tungsten bronze structured-PBN could be suitable for capacitor applications.     

Anomalous High-Temperature Properties of BaPbO3-Based Solid Solutions

The thermal expansion, thermal stability, and electrical resistivity of the Ba_{1 – x} M _x Pb_{1 + y} O_{3 +} (M = Sr, Ca; 0 x 1.0, 0 y 0.2) and Ba_{1 – x} M" _x Pb_{1 – y} M" _y O_{3 +} (M" = K, La; M" = Sc, Sb; x, y= 0.01) ceramic materials were studied between 293 and 1073 K in air. The linear thermal expansion coefficient of the ceramics was found to increase abruptly at 700 K, from (10–14) × 10^–6K^–1in the range 300–600 K to (13–18) × 10^–6K^–1in the range 800–1000 K. The electrical resistivity of the ceramics passes through a sharp maximum near 750 K, with the largest jump in resistivity at the compositions Ba_0.6Sr_0.4PbO₃and Ba_0.9Ca_0.1PbO₃. The anomaly in thermal expansion is likely associated with the rearrangement of the lead–oxygen polyhedra in the structure of the solid solutions, and the jump in resistivity is attributable to changes in the average oxidation state of Pb ions in the surface layer of the ceramics.     

Microstructure and relaxor ferroelectric properties of Bi2O3-doped strontium barium niobate ceramics

(1 − x) Sr_0.4Ba_0.6Nb₂O₆–xBi₂O₃ (0.00 ≤ x ≤ 0.20) ceramics were prepared by conventional solid-state reaction method. The microstructure, dielectric properties and P–E hysteresis loops of ceramics were investigated via X-ray diffraction, scanning electron microscope (SEM), Agilent E4980A and modified Sawyer–Tower circuit, respectively. XRD results showed the obtained ceramics were of tungsten bronze structure, and second phase Sr_0.4Ba_0.6Bi₂Nb₂O₉ was detected at high doping concentration. SEM results showed suitable Bi₂O₃ addition could reduce the sintering temperature and assist the grain growth. The dielectric characteristics exhibited diffuse phase transition phenomena, which were verified by linear fitting of the modified Curie–Weiss law. Besides, the relaxor ferroelectric properties of ceramics followed the Vogel–Fulcher relationship well. The P–E hysteresis loops became slimmer with increasing the Bi₂O₃ addition, leading to a gradually decrease in both remnant polarization (P_r) and coercive field (E_c).     

Synthesis of (BaxSr1−x)(Zn1/3Nb2/3)O3 ceramics by reaction-sintering process and microstructure

(Ba_xSr_1−x)(Zn_1/3Nb_2/3)O₃ complex perovskite ceramics produced by reaction-sintering process were investigated. Secondary phases ZnNb₂O₆ and (Cu₂Zn)Nb₂O₈ were found at the perovskite matrix grain boundaries. 98.5–99.8% of the theoretical density was obtained. In (Ba_0.5Sr_0.5)(Zn_1/3Nb_2/3)O₃ and (Ba_0.7Sr_0.3)(Zn_1/3Nb_2/3)O₃, the amount and volume of second phases decreased clearly at 1500 °C.     

Growth of highly orientated strontium barium niobate thin films on Si substrates through the sol–gel process using a K: SBN template layer

We report the growth of highly C-axis orientation of Sr _x Ba_1−x Nb₂O₆ (SBN) thin films on p-type (100) Si substrates by using a potassium-substituted SBN template layer with the sol–gel method. The crystallization of SBN thin films was found closely related to the potassium ion doping concentration and the postannealing temperature of the K-SBN template layer. Secondary ion mass spectrometry analysis showed that potassium elements were accumulated at the interface of the template layer and silicon substrate. SBN films postannealed at 750 °C with K-SBN template layer has a smaller full width at half maximum of X-ray rocking curve of 2.45° than that of 5.40° for the pure SBN films. By introducing a template layer, the surface morphologies of SBN films fabricated on silicon substrate were greatly improved.     

Crystal structure of (Ba1−x Lax) [Mg(1 + x)/3Nb(2−x)/3]O3 ceramics

The crystal structure of (Ba_1–x La _x )[Mg_{(1 + x)/3}Nb_(2–x)/3]O₃ (BLMN) ceramics with 0 x 1 was investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). When the La content, x, was above 0.1, the 1:2 ordered hexagonal structure found in Ba(Mg_1/3Nb_2/3)O₃ (BMN) was transformed into the 1:1 ordered cubic structure. The 1:1 ordered cubic structure was maintained up to x = 0.7. When x exceeded 0.7, however, BLMN exhibited a 1:1 ordered monoclinic structure, rather than a 1:1 ordered cubic structure. La(Mg_2/3Nb_1/3)O₃ (LMN) has a 1:1 ordered monoclinic P2₁/n structure with a = 5.6004 Å, b = 5.6414 Å, c = 7.9346 Å, and = 89.9819°. The monoclinic LMN has the in-phase and the anti-phase tilt of oxygen octahedra. The anti-parallel shift of A-site cations was also found in LMN.     

Dielectric and pyroelectric studies of Li-modified rare-earth dysprosium-doped barium strontium sodium niobate ceramics

This paper highlights the dielectric, pyroelectric, and resistivity studies of Ba_1.45Sr_2.4Dy_0.1Li _x Na_2−x Nb₁₀O₃₀ (x = 0 ≤ x ≤ 1.0) tungsten–bronze-structured ceramics. X-ray diffraction studies indicated single orthorhombic (mm2) phase supported by tolerance factor and average electronegativity difference. The lattice parameters, unit cell volume, axial ratio, and densities are calculated from XRD studies. The experimental densities obtained are about 95% to that of theoretical values. It is found that the unit cell volume enhanced up to Li_0.8. The effect of Li modification and Dy doping on ε_RT, and T _c in BSNN system are discussed. D.C. resistivity studies indicated the positive temperature coefficient of resistivity (PTCR) response in these compositions.     

A new series of mercury-based high-Tc superconductors (Hg, W)Sr2(Y1?x Cax)Cu2

A new series of superconducting mercury-based layered cuprates has been synthesized. X-ray diffraction indicates that the compounds with formula Hg_0.8W_0.2Sr₂Y_1–x Ca _x Cu₂O₆₊ (0.3x0.6) exhibit the 1212 structure with space groupP _4/mmm . The investigation of superconductivity determined by electrical resistance measurement shows that the superconducting transition temperature (T _c , onset) of Hg_0.8W_0.2Sr₂Y_0.4Ca_0.6Cu₂O₆₊ is up to 94 K.     

Synthesis and dielectric properties of Sr0.6 − x Ba0.4Na2x Nb2O6 solid solutions

We have prepared Sr_{0.6 ? x} Ba_0.4Na_2x Nb₂O₆ (0 ≤ 2x ≤ 0.3) solid solutions with the tetragonal tungsten bronze (TTB) structure, investigated the sequence of phase changes involved, and determined the lattice parameters of the solid solutions. The electrical properties of polycrystalline samples have been studied in broad frequency and temperature ranges. The results indicate that an increase in sodium content, accompanied by a reduction in the concentration of vacancies on the A site of the TTB structure, reduces the rate of dielectric relaxation.     

Effect of La/Sn co-substitution for Ba/Ta on crystal structure and dielectric properties of Ba5NdTi3Ta7O30 ceramics

The effects of La/Sn co-substitution for Ba/Ta were investigated for the modification of Ba₅NdTi₃Ta₇O₃₀ ceramics. The modified ceramics (Ba_5–x La _x )NdTi₃(Ta_7–x Sn _x )O₃₀ exhibited single tetragonal tungsten bronze phase for x<1.5, while a small amount of secondary phase BaTi₄O₉ was observed for x>1.5. The lattice constants decreased with increasing La/Sn content, while the axial ratio 10^1/2c/a decreased when x was below 1.5, then slightly increased. With increasing La and Sn content, the temperature coefficient of dielectric constant (at 1 MHz) was remarkably lowered from –1560 ppm/ °C to –286 ppm/ °C, while the dielectric constant gradually reduced, and the dielectric loss slightly increased. There were some clear relationships between the temperature coefficient and bond valence, tolerance factor: the temperature coefficient of dielectric constant linearly increased when the bond valence of the ions at B sites increased, while the same effect occurred when the tolerance factor decreased. In addition, the stability of the tetragonal tungsten bronze phase is discussed in relation to electronic difference and tolerance factor.     

Structure and dielectric properties of Ba1−xSrxCuSi2O6-Ba0.55Sr0.45TiO3 ferroelectric-dielectric composite ceramics

yBa_1?xSr_xCuSi₂O₆-(1?y) Ba_0.55Sr_0.45TiO₃ (x?=?0, 0.2 and y?=?10 wt%, 30 wt%) ferroelectric-dielectric composite ceramics were prepared by the solid-state sintering method. The relationship among phase composition, microstructures and dielectric properties has been investigated. By adjusting the content of the Ba_1?xSr_xCuSi₂O₆ and the content of Sr²⁺ in the Ba_1?xSr_xCuSi₂O₆, the effect of the dielectric material on BST was studied. With the increase of Ba_1?xSr_xCuSi₂O₆ content and the increase of the Sr²⁺ content, the dielectric peak of the composite material is gradually suppressed and broadened, and the Curie temperature (Tc) moves to the low temperature. The introduction of Ba_1?xSr_xCuSi₂O₆ reduced the permittivity of the composite material to a certain extent, at the same time, the dielectric tunability and quality factor (Q) value are maintained at a high level. The dielectric tunability of the four composite ceramics obtained is still higher than 10% under the applied electric field (at 30 kV/cm). The 30 wt% BCSO–70 wt% BST55 system and the 30 wt% BSCSO–70 wt% BST55 system has lower dielectric permittivity (830, 577), higher dielectric tunability (17.3%, 10.2% at 30 kV/cm) and a decent Q value (149 at 1.25 GHz, 168 at 1.31 GHz).

     

Influence of strontium on the cubic to ordered hexagonal phase transformation in barium magnesium niobate

Oxides of the type Ba_3-xSr_xMgNb₂O₉ were synthesized by the solid state route. Thex = 0 composition (Ba₃MgNb₂O₉) was found to crystallize in a disordered (cubic) perovskite structure when sintered at 1000C. For higher Sr doping (x ≥ 0.5), there was clearly the presence of an ordered hexagonal phase indicated by the growth of superstructure reflections in the powder X-ray diffraction patterns. In all the compositions there was the presence of a minor amount of Ba_5-xSr_xNb₄O₁₅ phase which increased with Sr substitution up tox = 1 and then it remained nearly constant at about 5%. Samples sintered at 1300C showed the hexagonally ordered phase for the entire range of composition (0 ≤x ≤ 3). The degree of ordering being considerably greater than in the 1000C heated samples as evidenced by several superstructure reflections