Study on properties of BaxSmyTi7O20 ceramics with CaO-SiO2-B2O3 glass

The effect of CaO-SiO₂-B₂O₃ (CSB) glass addition on the sintering temperature and dielectric properties of Ba_xSm_yTi₇O₂₀ ceramics has been investigated using X-ray diffraction, scanning electron microscopy and differential thermal analysis. The CSB glass starts to melt at about 970 °C, and a small amount of CSB glass addition to Ba_xSm_yTi₇O₂₀ ceramics can greatly decrease the sintering temperature from about 1350 to about 1260 °C, which is attributed to the formation of liquid phase. It is found that the dielectric properties of Ba_xSm_yTi₇O₂₀ ceramics are dependent on the amount of CSB glass and the microstructures of sintered samples. The product with 5 wt% CSB glass sintered at 1260 °C is optimal in these samples based on the microstructure and the properties of sintering product, when the major phases of this material are BaSm₂Ti₄O₁₂ and BaTi₄O₉. The material possesses excellent dielectric properties: ?_r = 61, tan δ = 1.5 × 10⁻⁴ at 10 GHz, temperature coefficient of dielectric constant is −75 × 10⁻⁶ °C⁻¹.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.     

Preparation, structure and dielectric properties of Ba4LaMNb3O15 (M = Ti, Sn ) ceramics

Two new cation-deficient hexagonal perovskites Ba₄LaMNb₃O₁₅ (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba₄LaTiNb₃O₁₅ has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (τ_f) +93 ppm °C⁻¹ at room temperature; Ba₄LaSnNb₃O₁₅ has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and τ_f −29 ppm °C⁻¹.     

Preparation and dielectric properties of BaCu(B2O5)-doped SrTiO3-based ceramics for energy storage

BaCu(B₂O₅) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO₃ ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu²⁺ and Ba²⁺, while further increase was owing to the increase of dissolved Ba²⁺ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO₃ ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm³ and energy efficiency of 98.83%.     

Dielectric and piezoelectric properties of Y2O3 doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free piezoelectric ceramics

Y₂O₃ doped lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (0-0.7 wt%) were synthesized by the conventional solid state reaction method, and the effect of Y₂O₃ addition on the structure and electrical properties was investigated. X-ray diffraction shows that Y₂O₃ diffuses into the lattice of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ to form a solid solution with a pure perovskite structure. The temperature dependence of dielectric constant of Y₂O₃ doped samples under various frequencies indicates obvious relaxor characteristics different from typical relaxor ferroelectric and the mechanism of the relaxor behavior was discussed. The optimum piezoelectric properties of piezoelectric constant d₃₃ = 137 pC/N and the electromechanical coupling factor k_p = 0.30 are obtained at 0.5% and 0.1% Y₂O₃ addition, respectively.     

Role of chromium ion valence states in ZnO-As2O3-Sb2O3 glass system by means of spectroscopic and dielectric studies

ZnO-Sb₂O₃-As₂O₃ transparent glasses containing small concentrations of chromium ions (introduced as Cr₂O₃) ranging from 0 to 0.2 mol% is prepared. A number of studies viz., XRD, SEM, DTA, optical absorption, FT-IR, Raman, ESR spectra, magnetic susceptibility and dielectric properties (constant ?′, loss tan δ, ac. conductivity σ_ac over a wide range of frequency and temperature as well as dielectric breakdown strength at room temperature) of these glasses have been carried out as a function of chromium ion concentration. The results have been analysed in the light of different oxidation states of chromium ions. The analyses indicates that when the concentration of chromium ions is low, these ions mostly exist in Cr⁶⁺ and Cr⁵⁺ states, occupy network forming positions with CrO₄²⁻ and CrO₄³⁻ structural units respectively and increase the rigidity of the glass network. When the concentration of chromium ions is gradually increased, these ions seem to be existing mostly in Cr³⁺ state.     

Effect of Pb(Fe1/2Nb1/2)O3 modification on dielectric and piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbZr0.52Ti0.48O3 ceramics

10 mol% Pb(Fe_1/2Nb_1/2)O₃ (PFN) modified Pb(Mg_1/3Nb_2/3)O₃-PbZr_0.52Ti_0.48O₃ (PMN-PZT) relaxor ferroelectric ceramics with compositions of (0.9 − x)PMN-0.1PFN-xPZT (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared. X-ray diffraction investigations indicated that as-prepared ceramics were of pure perovskite phase and the sample with composition of x = 0.8 was close to morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase. Dielectric properties of the as-prepared ceramics were measured, and the Curie temperature (T_c) increased sharply with increasing PZT content and could be higher than 300 °C around morphotropic phase boundary (MPB) area. At 1 kHz, the sample with composition of x = 0.1 had the largest room temperature dielectric constant ?_r = 3519 and maximum dielectric constant ?_m = 20,475 at T_m, while the sample with composition of x = 0.3 possessed the maximum dielectric relaxor factor of γ = 1.94. The largest d₃₃ = 318 pC/N could be obtained from as-prepared ceramics at x = 0.9. The maximum remnant polarization (P_r = 28.3 μC/cm²) was obtained from as-prepared ceramics at x = 0.4.     

Electrical properties tailoring in Ni-particle-dispersed (Ba0.95Ca0.05)(Ti0.96Zr0.04)O3 composites

Ni-particle-dispersed (Ba_0.95Ca_0.05)(Ti_0.96Zr_0.04)O₃ (BCTZ/Ni) piezoceramic composites were prepared via sintering at 1300 °C in industrial N₂ gas. Structural characterizations showed that the metallic Ni was not oxidized and the BCTZ preserved the perovskite structure. The Ni particles were uniformly distributed in the BCTZ ceramic matrix. The relative dielectric constant ?_r of the BCTZ/Ni composites increased from 1362 to 3910 with increasing Ni content from 0 to 20 vol.%, which is explained by the Maxwell equation as well as the micro-capacitor model. The percolation theory of insulator–metal transitions is also applied to correlate the rapid increase of dielectric constant with Ni content. The piezoelectric constant d₃₃ gradually decreased from 230 to 50 pC N⁻¹, giving a gradient profile of piezoelectric property. We demonstrate that the electrical properties can be effectively tailored by dispersing metal particles into piezoceramics.     

Influence of Bi2O3 and CuO addition on low-temperature sintering and dielectric properties of Ba0.6Sr0.4TiO3 ceramics

In this study, we tried to lower the sintering temperature of Ba_0.6Sr_0.4TiO₃ (BST) ceramics by several kinds of adding methods of Bi₂O₃, CuO and CuBi₂O₄ additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi₂O₄ was the most effective way for lowering the sintering temperature of BST. When CuBi₂O₄ of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST.     

Oxygen vacancy ordering in strontium doped rare earth cobaltate perovskites Ln1−xSrxCoO3−δ (Ln = La, Pr and Nd; x > 0.60)

A family of Sr-doped perovskite compounds Ln_1−xSr_xCoO_3−δ (Ln = La³⁺, Pr³⁺ and Nd³⁺; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 °C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm³⁺ and an upper limit of Sr²⁺ solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancy ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln³⁺/Sr²⁺ cation ordering was observed.     

Microstructure and electrical properties of Sm2O3 doped Bi2O3-based ZnO varistor ceramics

The dependence of the bulk density, microstructure and dc electrical properties of bismuth oxide (Bi₂O₃)-based zinc oxide (ZnO) varistor ceramics for various samarium oxide (Sm₂O₃) contents was investigated. The value of bulk density was found to 5.43-5.50 g cm⁻³ with Sm₂O₃ (mol%) content. The maximum value of bulk density is observed to be 5.50 for 0.30 mol% Sm₂O₃ containing varistor ceramics. The grain sizes for all the samples calculated from the scanning electron micrographs were found to decrease as Sm₂O₃ increases. The presence of ZnO phases, Bi-rich phases, spinel phases and Sm₂O₃ phases were observed in the samples by the energy dispersive X-ray analysis and X-ray diffraction analysis. As the Sm₂O₃ amount increased in the Bi₂O₃-based ZnO varistor ceramics, the nonlinear coefficient, α increased up to 0.10 mol%, reaching a maximum value of 58 and then decreased. The breakdown electric field, E_b, increased with the increase of Sm₂O₃ content with a maximum value of 3220 V cm⁻¹ for the 0.75 mol% Sm₂O₃ doped ZnO varistor ceramics. The leakage current, I_L, showed a minimum value of 1.10 μA for the composition of 0.30 mol% Sm₂O₃ doped Bi₂O₃-based ZnO varistor ceramics. The 0.30 mol% Sm₂O₃-doped Bi₂O₃-based ZnO varistor ceramics sintered at 1200 °C exhibited a good stability for dc accelerated aging stress of 0.90 V_1 mA/90 °C/12 h.     

A novel red long lasting phosphorescent (LLP) material β-Zn3(PO4)2:Mn, Sm

A novel red long lasting phosphorescent materials β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺ is firstly synthesized by high-temperature solid-state reaction. The influence of Sm³⁺ ions on luminescence and long lasting phosphorescence properties of Mn²⁺ in phosphor β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺ are systematically investigated. It is found that the red phosphorescence (λ = 616 nm) performance of Mn²⁺ ion such as brightness and duration is largely improved when Sm³⁺ ion is co-doped into the matrix in which Mn²⁺ ion acts as luminescent center and Sm³⁺ ion plays an important role of electron trap. Thermoluminescence spectrums show that there exists one peak in β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺, the depth of which is 0.33 eV, and that there are three peaks in β-Zn₃(PO₄)₂:Mn²⁺, among which the depth of the lowest temperature peak in β-Zn₃(PO₄)₂:Mn²⁺ is 0.37 eV. Such differences in the trap depth result in the improvement of red long lasting phosphorescence of Mn²⁺ in present matrix.     

Structural characterization of 0.5PbMg1/3Nb2/3O3-0.5BaxPb(1−x)TiO3 powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg_1/3Nb_2/3)O₃-0.5(Ba_xPb_(1−x)TiO₃) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h.     

Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

Structure analysis on the Ba3Mg(Ta1−xNbx)2O9 ceramics: Coexistence of order and disorder

The Ba₃ZnTa₂O₉ (BZT) and Ba₃MgTa₂O₉ (BMT) ceramics, a family of A₃B²⁺B⁵⁺₂O₉ complex perovskites, are extensively utilized in mobile based technologies due to their intrinsic high unloaded quality factor, high dielectric constant and a low (near-zero) resonant frequency temperature coefficient at microwave frequencies. The preparation conditions as well as size and nature of B cations have a profound effect on the final dielectric properties. In this article, we report the effect of Nb⁵⁺ at the Ta⁵⁺ site on the BMT structure prepared at four synthesis temperatures (1300, 1400, 1500 and 1600 °C). The analysis has been carried out using the Rietveld technique on the X-ray powder diffraction data. Results suggest that both the preparation temperatures and Nb⁵⁺ content have significant effect on the ordering of B cations in the Ba₃Mg(Ta_1−xNb_x)₂O₉ solid solution. A disordered (cubic) structure is preferred by the 1300 °C compounds. The weight percentage of the ordered (trigonal) phase escalates, for a given composition, with increasing calcination temperature. A fully ordered trigonal arrangement exists only for x = 0.0 and 0.2 compounds calcined at 1600 °C, and the rest are biphasic (cubic and trigonal). The increase in the cubic fraction upon Nb⁵⁺ augmentation suggests that the solid solution leans more toward the disordered structural arrangement of B²⁺ and B⁵⁺ cations.     

The magnetic properties of Bi0.9Ba0.1Fe0.81M0.09Ti0.1O3 solid solutions (M = Co, Mn, Sc, Al)

Solid solutions with general formula Bi_0.9Ba_0.1Fe_0.81M_0.09Ti_0.1O₃ (M = Co, Mn, Sc, Al) together with parental Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ were prepared by the traditional solid state reaction method. Their structural, room temperature magnetic, and dielectric properties were investigated. X-ray diffraction analysis indicated that all samples maintained original R3c space group. M–H hysteresis loop of Co³⁺ doped sample saturated at an applied field of 1 T with spontaneous magnetization of 1.735 emu/g, while Mn⁴⁺ substitution enhanced the magnetization of Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ less strongly; addition of Sc³⁺ helped decrease magnetic coercive field while Al³⁺ modified sample exhibited paramagnetic M–H hysteresis loop. Differential scanning calorimetry was applied to determine the Neel temperature (T_N) and the T_N for undoped, Co³⁺, Mn⁴⁺, Sc³⁺, Al³⁺ doped solid solutions were 318.1, 324.3, 335.7, 293.9 and 295.8 respectively. Sc³⁺ substitution had little influence on the dielectric properties of Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ while Al³⁺ doping improved its dielectric constant. In contrast, Co³⁺, Mn⁴⁺ doped samples showed decreased permittivity but inhibited tan δ at frequencies larger than 30 kHz.     

Synthesis of (1 − x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 ceramic powder via ethylenediaminetetraacetic acid precursor

(1 − x)Ca_2/5Sm_2/5TiO₃-xLi_1/2Nd_1/2TiO₃ (CSLNT) ceramic powder was prepared by a liquid mixing method using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. TG, DTA, XRD and TEM characterized the precursors and derived oxide powders. When x = 0.3, perovskite CSLNT was synthesized at 1000 °C for 3 h in air. The CSLNT (x = 0.3) ceramics sintered at 1200 °C for 3 h show excellent microwave dielectric properties of ?_r = 99, Q_f = 6200 GHz and τ_f = 9 × 10⁻⁶ °C⁻¹.     

Crystal structure and Eu/Tb doped luminescent properties of a new borate Ba3BiB9O18

Undoped and doped either by Eu³⁺ or Tb³⁺ bismuth borate Ba₃BiB₉O₁₈ was structurally characterized and analyzed by fluorescence spectroscopy. Belonging to synthetic borate member of the family Ba₃XB₉O₁₈, layers of planar triangular B₃O₆ groups connecting with deformed BaO₆ hexagons are interleaved by 9-coordinate Ba atoms, and 6-coordinate Bi atoms. Its crystal structure was determined and refined from powder X-ray diffraction data by the Rietveld method and the results showed that Ba₃BiB₉O₁₈ belongs to space group P6₃/m with unit cell dimensions of a = 7.1999(2) Å, c = 17.3567(6) Å, and z = 2. Curves of differential thermal analysis and thermogravimetric analysis showed that Ba₃BiB₉O₁₈ is a congruent melting compound and chemically stable above 728 °C. Ba₃Bi_1−xEu_xB₉O₁₈ and Ba₃Bi_1−xTb_xB₉O₁₈ form a continuous solid solution from x = 0.01 to x = 0.9. The ultraviolet excited photoluminescence intensity increased with both Eu³⁺ and Tb³⁺ concentration in the matrix of Ba₃BiB₉O₁₈. There may be an interesting correlation between spectroscopic properties and lattice structural features of doped Ba₃BiB₉O₁₈.     

Synthesis and characterisation of the double perovskite Ba2(Zn0.5Ti0.5X)O6 (X = Nb, Ta) ceramics

Ba₂(Zn_0.5Ti_0.5X)O₆ compounds from the general ABO₃ perovskite family were synthesized by the classical solid-state route for X = Nb and Ta with various A/B ratios (1.005, 1 and 0.995). After the calcination step at 1100 °C, both compounds (X = Nb and Ta) contain mainly the cubic disordered ‘Ba₂(Zn_0.5Ti_0.5X)O₆’ phase but traces of BaTiO₃ and secondary phases are often detectable. Nevertheless, after the sintering stage at higher temperature (from 1300 to 1500 °C) and for all A/B ratios investigated, Ti enters into the cubic perovskite structure, resulting in the formation of a unique ‘Ba₂(Zn_0.5Ti_0.5X)O₆’ phase. Attractive dielectric properties have been measured on the tantalum-based compound for A/B = 0.995 (Q ∼2000 at 7.4 GHz and ? = 39.6) as well as on the niobium-based phase for A/B = 1.005 (Q ∼2200 at 6.1 GHz and ? = 54.8). All these characteristics were confirmed at 1 MHz and a linear dependence of the permittivity versus temperature from −60 to 180 °C has also been evidenced for both formulations. Sinterability, dielectric properties and microstructure of such compounds are discussed with respect to the stoichiometry.     

Tunable and microwave dielectric properties of Ba0.5Sr0.5TiO3-BaWO4 composite ceramics doped with Co2O3

Co₂O₃ doped BaWO₄-Ba_0.5Sr_0.5TiO₃ composite ceramics, prepared by solid-state route, were characterized systematically, in terms of their phase compositions, microstructure and microwave dielectric properties. Doping of Co₂O₃ promoted grain growth, reduced Curie temperature and broadened phase-transition temperature range of BaWO₄-Ba_0.5Sr_0.5TiO₃, which were attributed mainly to the substitution of Co³⁺ for Ti⁴⁺ at B site in the perovskite lattice. Dielectric diffusion behaviors of the composite ceramics were discussed. The composite ceramics all had dielectric tunability of higher than 10% at 30 kV/cm and 10 kHz, with promising microwave dielectric properties. Specifically, the sample doped with 0.2 wt.% Co₂O₃ exhibited a tunability of 20%, permittivity of 225 and Q of 292 (at 1.986 GHz), making it a suitable candidate for applications in electrically tunable microwave devices.