Effect of sintering atmosphere on the microstructure and dielectric properties of barium strontium titanate glass–ceramics

The sintering of barium strontium titanate glass–ceramics in nitrogen modified their dielectric properties significantly compared to the sintering in air. The experimental results demonstrate that the glass–ceramics sintered at low temperatures contain a major phase Ba₂TiSi₂O₈ (BTS), known as fresnoite. The fresnoite phase disappeared and the barium strontium titanate perovskite phase became the major phase when the sintering temperature was increased. In addition, the microstructure observation showed that both the proportion of crystal phase and the crystal size increase obviously with the increase of sintering temperature. Most importantly, impedance spectroscopy has been employed to study the electrical responses arising from the glass and the crystal phases in the glass–ceramics sintered at low temperatures and high temperatures. The magnitudes of impedance and modulus changed significantly for the glass–ceramics sintered at the two temperature ranges. The activation energy calculated from the complex impedance, complex modulus and dc conductivity suggests that the dielectric relaxation for the glass phase and the glass–crystal interface may be attributed to the motion of the dipole associated with oxygen vacancy. And for the barium strontium titanate perovskite glass–ceramics, the motion of the electrons from the second ionization of oxygen vacancies leads to dc electrical conduction. The mechanism for the giant dielectric properties of the glass–ceramics sintered at high temperatures in nitrogen is discussed.     

Effects of glass components on crystallization and dielectric properties of BST glass–ceramics

Crystallization behavior was studied for glass powders in which some portions of AlF₃ in the net composition of 60(Ba_0.7Sr_0.3)TiO₃–25SiO₂–15AlF₃ were replaced with Ga₂O₃ or Bi₂O₃. The replacement with Ga₂O₃ resulted in a progressive increase in crystallization temperature, which effectively assisted the viscous sintering of glass powders to produce densified BST glass–ceramics at relatively lower temperatures. For the Bi₂O₃-replaced glass powders, an increasing amount of Bi₂O₃ replacement lowered the crystallization temperature and yielded less densified glass–ceramics containing a considerable amount of glassy phase. The temperature dependence of permittivity was estimated for the Ga₂O₃- and Bi₂O₃-replaced glass–ceramics as a function of sintering conditions and the amount of replacement, respectively.     

Effect of La2O3 additive on the dielectric properties of barium strontium titanate glass–ceramics

The barium strontium titanate (Ba_xSr_1–xTiO₃) glass–ceramics doped with different content of La were prepared via controlled crystallization. Phase compositions, microstructure and dielectric behaviors were investigated systematically. The results revealed that La₂O₃ additives had little influence on the dielectric constant but significantly changed the microstructure of the glass–ceramics, which led to improved breakdown strength (BDS). The optimized energy-storage density of 3.18 J/cm³ was achieved in the glass–ceramics with 1.0 wt% La₂O₃ content which is 2.56 times higher than pure BST glass–ceramics, suggesting glass–ceramics of this composition could be an attractive candidate for energy-storage applications.     

Structure and dielectric properties of potassium niobate nano glass–ceramics

Glasses in the composition of 25K₂O-25Nb₂O₅-50SiO₂ (mol %) have been prepared by melt quenching technique and isothermally heat-treated at 800 °C for different duration (0–200 h). The formed nanocrystalline KNbO₃ phase, crystallite size and morphology are examined by X-ray diffraction, Fourier transform infrared reflection spectroscopy, field emission scanning and transmission electron microscopes. The frequency and temperature dependent dielectric constant and loss tangent are measured in the frequency and temperature ranges 0.1–1000 kHz and 200–500 °C respectively. The dielectric constant and loss tangent are found to decrease with increasing frequency and increase with increasing temperature. The dielectric constant and loss tangent versus temperature curve at different frequency revealed the phase transition of KNbO₃ from paraelectric cubic to ferroelectric tetragonal around 425 and 397 °C (Curie temperature) for nano glass–ceramics obtained after 1 and 200 h heat-treatment respectively.     

Influence of crystallization time on microstructures and dielectric properties of tungsten–bronze glass–ceramics

A glass with a composition of 22.5SrO–22.5BaO–15Nb₂O₅–40SiO₂ (mol %) was prepared by a melt-quenching method and then heat-treated at 950 °C for different crystallization time. Microstructure observations were carried out using scanning electron microscope and dielectric properties were measured by a LCR meter. The experimental results show that volume fraction of the crystalline phase increased, dielectric constant maximum enhanced, and Curie temperature shifted as the crystallization time is prolonged. The decrease in the Curie temperature for the sample crystallized at 950 °C for 1 h is considered to be caused by the clamping effect from the glass matrix or small compositional fluctuation. Impedance spectroscopy has been employed to study the polarization contributions arising from the glass and crystalline phases in the glass–ceramics for different crystallization time. With the increase in crystallization time, the magnitudes of impedance and modulus as well as the relaxation frequency changed significantly. The activation energy calculated from the relaxation frequency increased for the glass phase due to a denser network structure, while the crystalline phase showed a slight decrease implying there is no change in its polarization mechanism.     

Role of MgF2 on properties of glass–ceramics

Formation of machinable glass–ceramic in the system MgO–SiO₂–Al₂O₃–K₂O–B₂O₃–F with and without addition of MgF₂ has been investigated. Crystallization of glass sample was done by controlled thermal heat treatment at nucleation and crystallization temperatures. The results showed that MgF₂ in high concentration had a synergistic effect and enhanced the formation of interlocked mica crystals. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses were changed in the range of 235–405 kJ/mol, while the crystallization activation energies of samples with addition of MgF₂ were changed in the range of 548–752 kJ/mol.     

Effect of composition on the dielectric properties and thermal conductivity of α-SiAlON ceramics

Journal of Materials Science: Materials in Electronics - In this study, a series of dense Ym/3Si12-(m+n)Alm+nOnN16-n (m?=?1.1–1.5, n?=?1.0) ceramics were prepared by...     

Effect of the glass melting condition on the processing of phosphate-based glass–ceramics with persistent luminescence properties

In this paper, we discuss the impact of the temperature and the duration of the melting on the persistent luminescence properties of phosphate glasses within the P₂O₅–Na₂O–CaO and P₂O₅–Na₂O–SrO systems prepared using a standard melting process in normal atmosphere by adding Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ microparticles in the glass batch before melting. Glasses with persistent luminescence properties can be successfully prepared if the melting conditions are carefully controlled.     

Effect of electric field on the microstructure and electrical properties of (In + Ta) co-doped TiO2 colossal dielectric ceramics

Journal of Materials Science: Materials in Electronics - Flash-sintering is a promising method for shorting the processing time, reducing the sintering temperature, and refining grain. Here, we...     

Effect of surface etching on interphase and elastic properties of a biocomposite reinforced using glass–silica particles

Biopolymer based composites are designed using glass–silica reinforcement. Surface etching of spherical glass–silica particles is performed using chemical and physical treatments. In particular, treatment with hydrofluoric acid proved to be efficient to achieve acceptable anchoring effect. Experimental testing of thermomoulded composites confirms that samples with chemically modified microbeads have improved mechanical properties, irrespective of phase content. A quantitative evaluation of the improvement of the starch/glass–silica interphase properties is achieved using a finite element model. Generation of typical microstructures is used to simulate phase arrangement and interphase properties. Microstructures are meshed taking into account the interphase region. Finite element results indicate that for all samples, interphase Young’s modulus is lower than those of the intrinsic materials. The thickness weighted interface modulus increases for composites where the mechanical adhesion is improved using HF chemical treatment.     

Influence of La–B–Zn glass on the sintering and microwave dielectric properties of Ca–Nd–Ti ceramics

The effects of La₂O₃–B₂O₃–ZnO (LBZ) glass on the sintering behaviors, phase structures, microstructures and the microwave dielectric properties of perovskite type Ca_0.6Nd_0.26TiO₃ (CNT) ceramics were studied. It indicates that the LBZ glass has an obvious effect on lowering the sintering temperature without damaging the microwave dielectric properties of the CNT ceramics. Small amounts of LBZ glass significantly lowered the sintering temperatures of CNT ceramics and obtained excellent microwave dielectric properties. However, too much LBZ glass is leading to inferior dielectric properties. The CNT ceramics doped with 3 wt% LBZ can be well sintered at 975 °C for 4 h and shows good properties: ε_r = 87.87, Q × f = 8132 GHz (f = 3.3 GHz), τ_f = +244.63 ppm/°C.     

Effect of BaO on crystallization,sintering, and properties of MgO-Al2O3-SiO2 glass–ceramics

Journal of Materials Science: Materials in Electronics - The effect of BaO on the crystallization, sintering, and properties of MgO-Al2O3-SiO2 glass–ceramics was investigated. The sintering...     

Effect of the POSS–Polyimide nanostructure on its mechanical and electrical properties

Nanocomposite films consisted of Polyhedral Oligomeric Silsesquioxane (POSS) filler in a Polyimide (PI) matrix were prepared. The effect of the nanocomposites’ structure on its mechanical and electrical properties was evaluated with respect to survival in the low Earth orbit (LEO) environment. The POSS–PI structure consists of POSS nano-aggregates formed in the bulk and on the surface. The aggregates’ size and distribution are POSS content-dependant. The fracture mechanism during hypervelocity impact at extreme temperature conditions was studied. The hypervelocity impacts of the POSS–PI films result in a brittle fracture, compared to ductile fracture in the case of PI, and in formation of radial cracks. A model based on formation and coalescence of voids around the aggregates, when load is applied, is suggested to explain the effect of the POSS content on the POSS–PI fracture mechanism. The size and density of the POSS aggregates also affect the nanocomposite’s volume electrical resistivity. An inverse dependence exists between the POSS aggregates’ surface density and the nanocomposites’ volume electrical resistivity.     

Effect of atmosphere on the electrical properties of TiO2–SnO2 varistor systems

This work illustrates the advancement of research on TiO₂-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO₂-based varistor ceramics. Dopants like Ta₂O₅, Nb₂O₅, and Cr₂O₃ have an especial role in the barrier formation at the grain boundary in the TiO₂ varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of Cr_Ti is to increase the O and O₂ adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O₂ adsorbed at the grain boundary. In this paper, TiO₂ and (Sn,Ti)O₂-based studies of polycrystalline ceramics, which show a non-linear I–V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications.     

Effect of CaO-doped in NiMn2O4–LaMnO3 composite ceramics on microstructure and electrical properties

The composite ceramics (NiMn₂O₄)_0.50(La_1?x Ca _x MnO₃)_0.50 (0?≤?x?≤?0.3) consisting of spinel-structured NiMn₂O₄ and perovskite-structured CaO-doped LaMnO₃ were prepared by classical solid state reaction. The X-ray diffraction (XRD) patterns have shown that the major phases presented in the sintered samples are NiMn₂O₄ compounds with a spinel structure, La_1?x Ca _x MnO₃ with a perovskite structure. The Scanning Electron Microscope (SEM) pictures have exhibited that the grain size of the composite ceramics decreases from ca. 6.5 to 2.0?μm as the mole fraction of CaO increases from 0 to 0.3. The ρ _25?°C and B _25/50 constants of the composite samples are in the range of 0.234–8.61?Ω?cm and 2,600–2,962?K, respectively. In particular, CaO-doped leads to a decrease in the resistance drift of the (NiMn₂O₄)_0.50(La_1?x Ca _x MnO₃)_0.50 composite NTC (negative temperature coefficient) ceramics after aging test. This indicates that the CaO-doped (NiMn₂O₄)_0.50(La_1?x Ca _x MnO₃)_0.50 NTC ceramics display high electrical stability in comparison with the Ca-free (NiMn₂O₄)_0.50(LaMnO₃)_0.50 ceramics. The X-ray photoelectron spectroscopy (XPS) analysis verifies that the valence states of the manganese ions have a highly mixed state of Mn²⁺, Mn³⁺ and Mn⁴⁺ at B site. And the electrical conduction of the composite ceramics can be elaborated by the ions migration mechanism.     

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.     

Synthesis and piezoelectric properties of PZT-based glass–ceramics

Glass–ceramics based on a soft piezoelectric of composition (Pb_0.94Sr_0.06)(Zr_0.53Ti_0.47)_0.997Mn_0.004O₃ (PSZTM) have been synthesized using three different glass systems by sol–gel method. The effect of the different glass systems on the crystallization of the perovskite phase, PSZTM have been studied using XRD and DTA. The piezoelectric characteristics of the different glass–ceramic systems have been determined and are correlated with the crystallization behaviour, crystalline phase and microstructure.     

Effect of iron on the electrical properties of lead–bismuth glasses

Semiconducting oxide glasses of the system (80 − x)Bi₂O₃–20PbO–xFe₂O₃, where x = 5, 10 and 15 mol.%, were prepared and investigated for dielectric properties in the frequency range 120–100 KHz and temperature range 300–550 K. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. The ac conductivity results suggest that the correlated barrier hopping (CBH) is dominant in ac conductivity.