Dielectric properties and microstructure of TiO2 modified (ZnMg)TiO3 microwave ceramics with CaO–B2O3–SiO2

The low-fired (ZnMg)TiO₃–TiO₂ (ZMT–TiO₂) microwave ceramics using low melting point CaO–B₂O₃–SiO₂ as sintering aids have been developed. The influences of Mg substituted fraction on the crystal structure and microwave properties of (Zn_1−x Mg _x )TiO₃ were investigated. The result reveals that the sufficient amount of Mg (x ≥ 0.3) could inhibit the decomposition of ZnTiO₃ effectively, and form the single-phase (ZnMg)TiO₃ at higher sintering temperatures. Due to the compensating effect of rutile TiO₂ (τ_f = 450 ppm/°C), the temperature coefficient of resonant frequency (τ_f) for (Zn_0.65Mg_0.35)TiO₃–0.15TiO₂ with biphasic structure was adjusted to near zero value. Further, CaO–B₂O₃–SiO₂ addition could reduce the sintering temperature from 1150 to 950 °C, and significantly improve the sinterability and microwave properties of ZMT–TiO₂ ceramics, which is attributed to the formation of liquid phases during the sintering process observed by SEM. The (Zn_0.65Mg_0.35)TiO₃–0.15TiO₂ dielectrics with 1 wt% CaO–B₂O₃–SiO₂ sintered at 950 °C exhibited the optimal microwave properties: ε ≈ 25, Q × f ≈ 47,000 GHz, and τ_f ≈ ± 10 ppm/°C.     

Synthesis and properties of glasses in the K2O–SiO2–Bi2O3–TiO2 system and bismuth titanate (Bi4Ti3O12) nano glass–ceramics thereof

Glasses were prepared by the melt-quench technique in the K₂O–SiO₂–Bi₂O₃–TiO₂ (KSBT) system and crystallized bismuth titanate, BiT (Bi₄Ti₃O₁₂) phase in it by controlled heat-treatment at various temperature and duration. Different physical, thermal, optical, and third-order susceptibility (χ³) of the glasses were evaluated and correlated with their composition. Systematic increase in refractive index (n) and χ³ with increase in BiT content is attributed to the combined effects of high polarization and ionic refraction of bismuth and titanium ions. Microstructural evaluation by FESEM shows the formation of polycrystalline spherical particles of 70–90 nm along with nano-rods of average diameter of 85–90 nm after prolonged heat treatment. A minor increase in dielectric constants (ε_r) has been observed with increase in polarizable components of BiT in the glasses, whereas a sharp increase in ε_r in glass–ceramics is found to be caused by the formation of non-centrosymmetric and ferroelectric BiT nanocrystals in the glass matrix.     

Microwave dielectric properties of (1 − x)(Mg0.4Zn0.6)2SiO4–xCaTiO3 composite ceramics

Phase formation, microstructure and microwave dielectric properties of (1 ? x)(Mg_0.4Zn_0.6)₂SiO₄–xCaTiO₃ (MZS-C) composite ceramics synthesized by using the conventional solid-state method were systematically investigated. Three phase structure was observed in all samples by using X-ray diffraction and the back scattering electron images. Mg₂SiO₄ can form a solid solution with Zn₂SiO₄, which improved sinterability of the MZS-C composite ceramics. As the CaTiO₃ content was increased from 0.06 to 0.14, dielectric constant ε _r and temperature coefficient of resonant frequency τ _f values of the MZS-C ceramics sintered at 1,180 °C for 4 h increased from 6.74 to 8.35 and ?41.5 to ?6.46 ppm/°C, respectively. Zero τ _f value can be obtained by properly adjusting the x value of the (1 ? x)MZS–xC ceramics. With increasing content of CaTiO₃, densification temperatures of the composite ceramics were decreased. The composite ceramic with x = 0.14 sintered at 1,180 °C for 4 h exhibited excellent microwave dielectric properties of ε _r = 8.35, Q × f = 28,125 GHz and τ _f = ?6.46 ppm/°C.     

Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al₂O₃–5B₂O₃) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε _r ), quality factor (Q × f) and temperature coefficient of resonant frequency (τ _f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B₂O₃ and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm³) as compared with pure alumina powders recycled from Al dross (3·55g/cm³ sintered at 1700 °C).     

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.     

Microwave dielectric properties and applications of Ba(Zn1/3Nb2/3)O3–Ca(Zn1/3Nb2/3)O3 composite ceramics by one-step synthesis method

(1 ? x) Ca(Zn_1/3Nb_2/3) O₃ ? xBa(Zn_1/3Nb_2/3)O₃ (short for CZN/BZN, x = 0–1.0) ceramics were prepared and investigated through the “one-step synthesis method” method. The structure of the system was analyzed using X-ray diffraction. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. Dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q × f) were measured in the microwave frequency region. Two dielectric properties were firstly in the rising tendency and then decreasing with the increased x. On the other hand, a good combination of microwave dielectric properties (ε_r = 24, Q × f = 23,510 GHz τ_f = ?9 ppm/°C) were obtained at x = 0.1. The compositions have excellent microwave dielectric properties and hence are suitable for ceramic capacitors or dielectric resonators applications.     

Properties of (Ti,Nb)Al–(Ti,Nb)5Si3 eutectic composite

Ti–40Al–5Si and Ti–39Al–5Si–2Nb (in at.%) alloys were studied as prospective high-temperature structural composites consisting of γ-(Ti,Nb)Al + α₂-(Ti,Nb)₃Al matrix and Ti₅Si₃ reinforcement. The alloys were prepared by arc melting under helium. Oxidation resistance was studied at 900 °C in air. Thermal stability of alloys was investigated by measuring room temperature hardness and compressive strength after long-term annealing at 900 °C. To prepare oriented composites, directional crystallization at rates of 5–115 mm/h was carried out by the floating zone technique. It was observed that the addition of 2% Nb to the Ti–40Al–5Si alloy does not modify eutectic structure. Niobium is almost uniformly distributed in all present phases. Both alloys show excellent oxidation resistance at 900 °C in air. The Nb-addition causes significant improvement of oxidation resistance due to the doping effect and increase of Al activity in the scales. Room temperature hardness and compressive strength of both as-cast alloys are similar – about 500 HV and 1600 MPa, respectively. Room temperature mechanical properties do not reduce significantly after 300 h annealing at 900 °C, due to a high morphological stability of eutectic silicides. Directionally solidified alloys consist of columnar Ti–Al grains elongated in crystallization direction and silicides. Niobium refines both Ti–Al grains and Ti₅Si₃ silicides. As a consequence, orientation and elongation of silicides in the Nb-containing alloy are reduced. In the Ti–Al–Si alloy directionally crystallized at 5–115 mm/h, the silicide interparticle spacing λ (in mm) is related to the crystallization rate R   (in mm/h) by a following expression: λ^1.33·R=0.32${\lambda }^{1.33}·R=0.32$. In the Nb-containing alloy, silicide interparticle spacing does not depend on the crystallization rate.     

Low-temperature sintering and microwave dielectric properties of 5Li2O–0.58Nb2O5–3.23TiO2 ceramics

The effect of B₂O₃ addition on the sintering, microstructure and the microwave dielectric properties of the 5Li₂O–0.58Nb₂O₅–3.23TiO₂ (LNT) ceramics have been investigated. It is found that the LNT ceramics could be sintered well at ∼880 °C with low-level doping of B₂O₃ (≤2 wt.%). Only Li₂TiO₃ solid solution (Li₂TiO₃ss) crystal structure could be detected for all the ceramics with various amounts of B₂O₃ addition from the X-ray diffraction (XRD) results. And interestingly, two phases with different color in SEM images are observed in B₂O₃-doped LNT ceramics. EDS results suggest that the two different phases are two Li₂TiO₃ss phases with different amount of Nb. In addition, there is no much degradation in the microwave dielectric properties with the B₂O₃ adding. In the case of 0.5 wt.% B₂O₃-doped samples sintered at 880 °C, good microwave dielectric properties of ?_r = 22, Q × f = 32,000 GHz, τ_f = 9.5 ppm °C⁻¹ are obtained.     

Microwave dielectric properties of BaO–TiO2–TeO2 ternary system

Besides the applications as optical functional materials, tellurium oxides also have attracted interest as microwave dielectric materials. Most TeO₂-based binary and ternary system have large negative temperature coefficient of resonant frequency (τ_f), which is not compatible for the low-temperature cofired ceramic. To compensate τ_f close to zero, two single-phase predecessors of BaTe₄O₉ and TiTe₃O₈ are synthesized in air at 530–560 and 620–680 °C, respectively. The two predecessors show exceptional dielectric properties and their τ_f are opposite. The BaO–TiO₂–TeO₂ ternary system compounds are investigated by adjusting the ratio of BaTe₄O₉ and TiTe₃O₈ and sintered at 520–580 °C to develop the microwave properties and compensate the τ_f. After sintered at 560 °C, the ceramic sample with the composition of 0.47BaTe₄O₉–0.53TiTe₃O₈ exhibits a dielectric permittivity of 28, a Q × f-value of 12,200 GHz, and a τ_f of 4.0 ppm/°C measured at 10 GHz.     

Microwave dielectric properties of Mg2SiO4–Ca1−ySm2y/3TiO3 composite ceramics

In this work, (1?x)Mg₂SiO₄–xCa_1?ySm_2y/3TiO₃ ceramics were fabricated using the conventional solid-state reaction method. When y?=?0.2, the effects of Ca_1?ySm_2y/3TiO₃ contents on microstructure, phase evolution, and microwave dielectric properties of the samples were studied. The X-ray diffraction showed that Mg₂SiO₄ and Ca_0.8Sm_0.4/3TiO₃ co-existed in composite ceramics. The dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) increased with the increasing content of Ca_0.8Sm_0.4/3TiO₃, while the quality factor (Q?×?f) decreased. At x?=?0.22, the (1?x) Mg₂SiO₄–xCa_0.8Sm_0.4/3TiO₃ ceramics sintered at 1325?°C for 3?h possessed optimal microwave dielectric properties: ε_r?~?11.89, Q?×?f value?~?32,703?GHz and τ_f?~?+?0.49?ppm/°C. As a result, the ε_r of (1?x) Mg₂SiO₄?+?xCa_1?ySm_2y/3TiO₃ ceramics could be adjusted in the range of 10.83 to 13.88 while the τ_f is near-zero.

     

Synthesis and photoluminescence properties of Eu-doped γ-Ca3(PO4)2

Eu³⁺-doped (1% and 3%) γ-Ca₃(PO₄)₂ was synthesized by high-pressure and high-temperature experimental method and the samples were characterized by X-ray diffraction. The luminescence properties of samples were investigated by emission and excitation spectra. The excitation spectra of Eu³⁺-doped γ-Ca₃(PO₄)₂ showed that samples were mainly attributed to Eu³⁺–O²⁻ charge-transfer band at 270 nm, and some sharp lines were also attributed to Eu³⁺ f–f transitions in near-UV regions with the strongest peaks at 395 nm. Under the 395 nm excitation, the intense red emission peak at 611 nm was observed. The strongest line (395 nm) in excitation spectra of those phosphors matched well with the output wavelength of UV InGaN-based light-emitting diodes (LEDs) chip. The luminescent properties suggested that Eu³⁺-doped γ-Ca₃(PO₄)₂ might be regarded as a potential red phosphor candidate for near-UV LEDs.     

Microstructures and dielectric properties of Ba0.5Sr0.5TiO3–Zn2TiO4 composite ceramics with low sintering temperature for tunable device applications

Ba_0.5Sr_0.5TiO₃–Zn₂TiO₄ composite ceramics with low dielectric constant and high tunability are fabricated at a relatively low sintering temperature of 1200 °C via the conventional solid-state reaction route. Zn₂TiO₄ and Ba_0.5Sr_0.5TiO₃ can be friendly coexistent in the composite material system. The dielectric constant is tailored from 2500 to 83 by manipulating the addition of Zn₂TiO₄ content from 0 wt.% to 80 wt.% weight ratio. The dielectric loss still keeps around 0.002 and the tunability is 10.3% under a DC-applied electric field of 30 kV/cm at 10 kHz for the 80 wt.% Zn₂TiO₄ added Ba_0.5Sr_0.5TiO₃ composite ceramics. These composite ceramics are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential tunable devices applications.     

Ferroelectric properties of (1 − x)Bi(Zn1/2Ti1/2)O3–xPbZrO3 ceramics

The (1 − x)Bi(Zn_1/2Ti_1/2)O₃–xPbZrO₃ solid solution ceramics were prepared by using solid-state reaction method, and their ferroelectric properties were investigated. It was found that the perovskite structure is stable for compositions with x ≥ 0.900. Within this composition range, the crystal structure of the solid solution preserves the orthorhombic symmetry of PbZrO₃ (PZ). The Curie point of the ceramics was found to decrease with increasing Bi(Zn_1/2Ti_1/2)O₃ (BZT) content. The intermediate ferroelectric phase of PZ was stabilized by BZT addition and exists within a much wider temperature range in the solid solution.     

Preparation and characterization of PEG–Mg(CH3COO)2–CeO2 composite polymer electrolytes for battery application

Composite polymer electrolytes based on poly(ethylene glycol) (PEG), magnesium acetate [Mg(CH₃COO)₂], and x wt% of cerium oxide (CeO₂) ceramic fillers (where x = 0, 5, 10, 15 and 20, respectively) have been prepared using solution casting technique. X-ray diffraction patterns of PEG–Mg(CH₃COO)₂ with CeO ₂ ceramic filler indicated the decrease in the degree of crystallinity with increasing concentration of the filler. DSC measurements of PEG–Mg(CH₃COO)₂–CeO₂ composite polymer electrolyte system showed that the melting temperature is shifted towards the lower temperature with increase of the filler concentration. The conductivity results indicate that the incorporation of ceramic filler up to a certain concentration (i.e. 15 wt%) increases the ionic conductivity and upon further addition the conductivity decreases. The transference number data indicated the dominance of ion-type charge transport in these specimens. Using this (PEG–Mg(CH₃COO)₂–CeO₂) (85-15-15) electrolyte, solid-state electrochemical cell was fabricated and their discharge profiles were studied under a constant load of 100 kΩ.     

Synthesis and properties of magnetic solid superacid: SO4/ZrO2–B2O3–Fe3O4

A magnetic SO₄²⁻/ZrO₂–B₂O₃–Fe₃O₄ solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO₂ from tetragonal to monoclinic phase is higher compared to the pristine SO₄²⁻/ZrO₂ material. The introduction of Fe₃O₄ endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification.     

Corrosion behaviour of sediment electro-codeposited Ni–Al2O3 composite coatings

Ni–Al₂O₃ composite coatings were produced by the sediment electro-codeposition (SECD) technique at various particle loadings and current densities. The submicron Al₂O₃ particles were found to distribute uniformly in the coating, and 12–18 vol.% particles can be incorporated in the coating depending on deposition current density and particle loading in the plating bath. Electrochemical corrosion testing was conducted in 0.9 wt.% NaCl solution. The results show that the incorporation of Al₂O₃ particles in the coating did not affect the general corrosion behaviour of the Ni coating. However, at higher anodic potentials approaching the breakdown potential and with prolonged polarization, the composite coatings showed deteriorated corrosion resistance in terms of increased anodic current density, reduced pitting potential and quicker breakdown of the passive film. The detrimental effects of Al₂O₃ particle incorporation could be explained by the existence of numerous boundaries between the particles and the matrix, which would serve as active sites for anodic dissolution and micro-pit formation.     

Crystal structure of uranyl μ3-oxoacetate [(UO2)3(μ3-O)2(OOCCH3)2(H2O)2]

The crystal structure of [(UO₂)₃(₃-O)₂(OOCCH₃)₂(H₂O)₂] consists of uranium coordination polyhedra (CPs) combined via common equatorial edges into ribbons, with ₃-O atoms being common for three CPs. The structure was compared with that of known complexes with ₃-oxo atoms.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 396–400.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

Sol–gel derived CaO–B2O3–SiO2 glass/CaSiO3 ceramic composites: processing and electrical properties

The CaO–B₂O₃–SiO₂ glass/CaSiO₃ ceramic (CBS/CS) composites were fabricated via sol–gel processing routes. Their densification behavior, structures and dielectric properties were investigated. The precursors of CBS glass and CS ceramic filler were firstly obtained via individual soft chemical route and then mixed together in various proportions. The results indicated that the structures of CBS/CS composites are characteristic of CS and CaB₂O₄ (CB) ceramic phases distributed in the matrix of glass phase at 800–950 °C. The CS ceramic phase not only acts as fillers, but nuclei for the crystallization of CBS glass as well such that the CS content exhibits an effect on the densification and dielectric properties of the composites. The CBS/CS composites with 10% CS sintered at 850 °C own dielectric properties of ε_r < 5 and tanδ = 6.4 × 10⁻⁴ at 1 MHz.     

Magnetoelectric properties of CoFe2O4–Pb(Zr0.52Ti0.48)O3 multilayered composite film via sol–gel method

CoFe₂O₄–Pb(Zr_0.52Ti_0.48)O₃ (CFO–PZT) multilayered composite film was prepared on Pt/Ti/SiO₂/Si substrate via a sol–gel method and spin-coating technique. Results show that PZT and CFO phases exist in the composite film, calcined at 700 °C, besides substrate phase, and no obvious impurity phases can be detected. The composite film exhibits layered structure with obvious boundary between CFO and PZT films. Ferroelectric and ferromagnetic properties were simultaneously observed in the composite film, evidencing the ferroelectric and ferromagnetic properties in the composite film. The composite film exhibits both good magnetic and electric properties, as well as, magnetoelectric (ME) effect. The saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic PZT layers. Ferroelectric hysteresis loops reveal that saturated polarization and remanent polarization of the composite film are lower than those of the pure PZT films. The composite film exhibits a very large ME effect, which makes the composite film attractive for technological applications as devices.     

Field-induced strain and polarization response in lead-free Bi1/2(Na0.80K0.20)1/2TiO3–SrZrO3 ceramics

The structure, field-induced strain, polarization and dielectric response of lead-free SrZrO₃-modified Bi_1/2(Na_0.80K_0.20)_1/2TiO₃ (abbreviated as BNKT–SZ100x, with x = 0–0.05) ceramics were investigated. The X-ray diffraction analysis of BNKT–SZ100x ceramics reveals no remarkable change in the crystal structure within the studied composition range. Around critical composition (x = 0.03) at a driving field of 6 kV mm⁻¹, large unipolar strain of 0.37% (S_max/E_max = 617) was obtained at room temperature. The ferroelectric and piezoelectric properties of BNKT ceramics were significantly increased at 2 mol%. At x = 0.02, remnant polarization reached a maximum value of 34 μC cm⁻², while the piezoelectric constant (d₃₃) attained maximum value of 190 pC/N. These results indicate that BNKT–SZ100x ceramics can be considered as promising candidate materials for lead-free piezoelectric actuator applications.