Effects of SrO–B2O3–SiO2 glass additive on dielectric properties of Ba(Fe0.5Nb0.5)O3 ceramics

SrO–B₂O₃–SiO₂ (SBS) glass powders were prepared and employed as sintering aids to reduce the sintering temperature of Ba(Fe_0.5Nb_0.5)O₃ (BFN) ceramics. The effects of glass content on the dielectric properties and breakdown strength of BFN ceramics have been investigated. The volume density characterization results of (1 ? x) BFN ? x SBS ceramics indicate that the sintering temperature of BFN ceramics decreased by 200–350 °C with SBS glass addition (when x = 0, 0.01, 0.03 and 0.05). The XRD patterns show BFN ceramics indicate cubic crystal structure and without the formation of a secondary phase. The dielectric constant and dielectric loss decreased gradually with increasing glass content, and the dielectric loss decreased by one order of magnitude with SBS glass addition (when x = 0.05). The breakdown strength of (1 ? x) BFN ? x SBS ceramics increase with increasing glass content, in which is about 33.90 kV/cm with SBS glass addition (when x = 0.05). These improvements in the dielectric characteristics of BFN ceramics have great scientific significance for their applications.     

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO₂ and CaMgSi₂O₆ phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (ε_r) of 5.3, dielectric loss (tanδ) of 2.97 × 10^?3 at 1 MHz, CTE value of 1.06 × 10^?6 K^?1, bulk density of 2.17 g/cm³, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (ε_r = 7.1, tanδ = 2.02 × 10^?3 at 1 MHz), low CTE (2.89 × 10^?6 K^?1), bulk density = 2.65 g/cm³ as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi₂O₆ crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10^?6 K^?1). The prepared LAS glass–ceramics have the potential for LTCC application.     

Effect of La2O3, CoO,Cr2O3 and MoO3 nucleating agents on crystallization behavior and magnetic properties of ferromagnetic glass–ceramic in the system Fe2O3·CaO·ZnO·SiO2

Preparation and characterization of ferromagnetic glass ceramic in the system Fe₂O₃·CaO·ZnO·SiO₂ with different nucleating agents was studied. The effect of La₂O₃, CoO, Cr₂O₃ and MoO₃ as nucleating agents was investigated. Differential thermal analysis; X-ray diffraction and transmission electron microscope were used to investigate thermal behavior, sequence of crystallization and microstructure of the samples. XRD analysis for as prepared samples revealed the crystallization of single magnetite phase. Heat treatment at 900 °C/2 h revealed the appearance of minor amounts of calcium silicate, hematite and cristobalite beside magnetite. TEM revealed crystallization of crystallite size in the range 50–100 nm. Lattice parameters, cell volume and crystallite size were stimulated from XRD data. Magnetic properties of quenched samples were measured under 20 kG.     

Effects of SrO–B2O3–SiO2 glass additive on densification and energy storage properties of Ba0.4Sr0.6TiO3 ceramics

SrO–B₂O₃–SiO₂ glass powders were prepared and employed as sintering aids to reduce the sintering temperature of Ba_0.4Sr_0.6TiO₃ ceramics. The effects of glass content and sintering temperature on the densification, dielectric properties and energy storage properties of Ba_0.4Sr_0.6TiO₃ ceramics have been investigated. The relative density characterization results indicate that densification of Ba_0.4Sr_0.6TiO₃ ceramics with glass content becomes apparently from sintering temperature of 1,060 °C. XRD results show all Ba_0.4Sr_0.6TiO₃ ceramics exhibit a perovskite structure without the formation of a secondary phase. The dielectric constant and dielectric loss decreased gradually with increasing glass content. The relationship between dielectric constant and breakdown strength was discussed using the thermochemical model. A discharged energy density of 0.44 J/cm³ with an energy efficiency of 67.4% was achieved for Ba_0.4Sr_0.6TiO₃ ceramic with 2.0 wt% glass addition sintered at 1,180 °C.     

Dielectric tunable properties of Ba0.5Sr0.5TiO3–MgMoO4 composite ceramics for microwave applications

(1?x) Ba_0.5Sr_0.5TiO₃–xMgMoO₄ (x = 0, 5, 10, 20 and 30 wt%) composite ceramics were prepared via solid state reaction processing. Their structure and dielectric properties were systematically characterized. The introduction of MgMoO₄ resulted in a change in lattice constant of the perovskite phase and partial reaction between MgMoO₄ and Ba_0.5Sr_0.5TiO₃ occurred in the sintering process. Both X-Ray Diffraction (XRD) and Back-scattered Electron Images (BEI) analysis show the co-existence of three phase structures of BST, MgMoO₄ and BaMoO₄. With increasing of MgMoO₄ content, the tunability of the composite ceramics was decreased due to the increase of the amount of non-ferroelectric phases. The Curie temperature Tc of the samples gradually shifted to low temperatures with increasing of MgMoO₄ content. Dielectric constant can be adjusted in the range from 2035 to 150, meanwhile maintain a relatively high tunability and Q values. The sample with 20 wt% MgMoO₄ possesses a tunability of 10 %, a low dielectric constant of 111 and an appropriate Q value of 183 (2.240 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.     

Sol–gel synthesis and spark plasma sintering of Ba0.5Sr0.5TiO3

Ultrafine Ba_0.5Sr_0.5TiO₃ powders were prepared by using barium nitrate, strontium nitrate, tetrabutyl titanate, and ammonia via citrate–nitrate combustion process at low temperature (500 °C), along with the X-ray diffraction (XRD), differential scanning calorimetry (DSC)/thermogravimetry analysis (TGA) and scanning electron microscopy (SEM) analytic reports. Spark plasma sintering was carried out to obtain the ultrafine crystalline BST and to improve the dielectric properity. It was found that the sintered BST showed ultrafine crystalline microstructure. At 25 °C, the dielectric constant and dissipation factor of the sintered sample were 1533 and 0.0063 at 10 kHz.     

Studies on magnetic and magnetoelectric properties of the NiFe2O4–Ba0.7Sr0.3TiO3 composites

The magnetic and magnetoelectric properties of magnetoelectric (ME) composites consisting of with nickel ferrite (NiFe₂O₄) and barium strontium titanate (Ba_0.7Sr_0.3TiO₃) were investigated. The composites were prepared by standard double sintering ceramic method. The X-ray diffraction analysis was carried out to confirm the phases formed during sintering and also to calculate the lattice parameters. The hysteresis measurements were done to determine saturation magnetization (M_s), remenance magnetization (M_r) and coercivity (H_c) of the samples. The magnetoelectric voltage coefficient (dE/dH)_H was studied as a function of intensity of the magnetic field. The measured magnetoelectric (ME) response demonstrated strong dependence on the volume fraction of NiFe₂O₄ and the applied magnetic field. A large ME voltage coefficient of about 560 μVcm⁻¹Oe⁻¹ was observed for 15% NiFe₂O₄ + 85% Ba_0.7Sr_0.3TiO₃ composite.     

Structural and magnetic properties of Ba0.7Sr0.3Fe12 − 2x Co x Ti x O19 M-type hexaferrites

We have studied the effect of “double” substitution in Ba_0.7Sr_0.3Fe_{12 ? 2x} Co _x Ti _x O₁₉ on the structural and magnetic properties of M-type barium hexaferrite. The basic composition of Ba_{1 ? x} Sr _x Fe₁₂O₁₉ obtained by heat-treating carbonate-hydroxide precipitates has been optimized (x = 0.3). 2Fe³⁺ → Co²⁺ + Ti⁴⁺ substitutions considerably reduce the coercive force (H _c) and increase the magnetization (M _s) relative to Ba_0.7Sr_0.3Fe₁₂ O₁₉.     

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...     

Effects of SrO–B2O3–SiO2 glass additive on the microstructure and dielectric properties of CaCu3Ti4O12

The effect of SrO–B₂O₃–SiO₂ glass additive (SBS) on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics was investigated. This SBS–added CCTO ceramics were prepared by the solid state reaction. The undesirable impurity phases Ca₃SiO₅ started appearing in the XRD patterns, suggesting a possible chemical reaction between CaTiO₃ and SiO₂ (the devitrification production of SBS glass). The SBS glass additive promoted the grain growth and densification of CCTO ceramics. Cole–Cole plots of conductance suggested that the resistivity grain boundary decreased with increasing amount of SBS glass (when x = 0–2 wt%), then increased (when x = 2–3 wt%). The addition of SBS glass was desirable to increase the dielectric constants (up to 10⁴) and lowered the dielectric losses of CCTO over the frequency range of 450–40 kHz at the relatively lower sintering temperature for relatively shorter sintering time (1,050 °C, 12 h).     

Studies on the structural,electrical and magnetic properties of LaCrO3, LaCr0.5Cu0.5O3 and LaCr0.5Fe0.5O3 by sol–gel method

The structural, electrical and magnetic properties of LaCr_0.5M_0.5O₃ (M = Cr³⁺, Cu²⁺ and Fe³⁺) synthesized by a sol–gel technique were studied. The X-ray diffraction pattern shows the structure to be orthorhombic and the size of the particles is around 100 nm as seen from the TEM images. The effects of Cu²⁺ and Fe³⁺ on the electrical properties of LaCrO₃ were studied using impedance spectroscopy at room temperature (RT). The properties of LaCr_0.5Cu_0.5O₃ were studied over a wide range of temperature from RT to 533 K. A maximum conductivity of 1.7 × 10^?3 S cm^?1 was observed for LaCr_0.5Cu_0.5O₃ at a measured temperature of 533 K. The impedance spectra indicate a negative temperature coefficient of resistance (NTCR) and also imply the conduction is through bulk of the material. The magnetic studies performed using a SQUID magnetometer interpret the antiferromagnetically ordered LaCrO₃ to behave ferromagnetically on the addition of Cu²⁺ and Fe³⁺, and the magnetization was found to be enhanced in the LaCr_0.5Fe_0.5O₃.     

Effects of Y2O3 and La2O3 addition on the crystallization of Li2O·Al2O3·4SiO2 glass-ceramic

Effects of adding Y₂O₃ and La₂O₃ on the crystallization of -quartz solid solution (ss) and the subsequent -quartz ss to -spodumene transformation of Li₂O·Al₂O₃·4SiO₂ glass-ceramic were investigated. Adding 4 mol% YO_3/2 or 8 mol % LaO_3/2 effectively improved the control of the crystallization process of the glass. Y₂O₃ did not effectively induce bulk crystallization of -quartz ss, but can reduce the rate of surface crystallization. La₂O₃ completely suppressed the surface crystallization and promoted a uniform, bulk crystallization of -quartz ss. For both the Y₂O₃- and La₂O₃-doped glasses, the kinetics for glass crystallization to -quartz ss was delayed as the doping level increased. Except for the 8 mol % LaO_3/2-doped glass in which no -spodumene was formed, the kinetics for the -quartz ss to -spodumene transformation for the doped glasses was enhanced compared with that for the undoped glass. For the 4 and 8 mol % YO_3/2-doped compositions, the relative amount of -spodumene to -quartz revealed an anomalous decrease trend with heating temperature in a particular temperature range. This can be explained by the surface crystallization characteristic, which induced an overlap of crystallization and -quartz ss to -spodumene transformation. Glass doped with 8 mol % LaO_3/2 exhibited an Avrami exponent of about 2.4 and an activation energy for crystal growth of -quartz ss of about 418 kJ mol^–1.     

Sintering behavior and microwave dielectric properties of TiO2 added Ba4(Sm0.5Nd0.5)28/3Ti18O54 ceramics with Li2O–Al2O3–B2O3 glass addition

Effect of Li₂O–Al₂O₃–B₂O₃ (LAB) doping on sintering behavior, microstructure and microwave dielectric properties of Ba_6?3x (Sm_1?y , Nd _y )_8+2x Ti₁₈O₅₄ + 2TiO₂ (x = 2/3 and y = 0.5; BSNTT) ceramics were investigated. The BSNTT ceramics doped with 2 wt.% LAB significantly lowered the sintering temperature by 250 °C compared to un-doped BSNTT (at 1,300 °C) without a serious degradation of the microwave dielectric properties. As the small amount of LAB content increased, the small amount of liquid phase increase in an amorphous state around the surface of the grain boundaries without secondary phase formation as observed in the X-ray diffraction and energy dispersive spectroscopy results. With increasing the content of LAB glass, both of dielectric constant (ε _r ) and quality factor (Q × f) value decreased. Typically, the BSNTT + 2 wt.% LAB ceramic which were well sintered at 1,050 °C for 3 h showed optimal microwave dielectric properties of: ε _r  = 61.1, Q × f = 5,856 GHz and τ _f  = +16.75 ppm/°C.     

Low temperature sintering and characteristics of K2O–B2O3–SiO2–Al2O3 glass/ceramic composites for LTCC applications

The K₂O–B₂O₃–SiO₂, K₂O–B₂O₃–SiO₂–2 %Al₂O₃, K₂O–B₂O₃–SiO₂–4 %Al₂O₃ glasses with different Al₂O₃ content were prepared. Different proportions (50, 55, 60, 65, 70 %) of the three glasses were respectively mixed with alumina ceramic-filler, then the mechanical and dielectric properties were investigated. The results showed K₂O–B₂O₃–SiO₂–2 %Al₂O₃ glass/alumina filler (glass:alumina = 60:40) had the excellent comprehensive properties, so further study was continued with part of alumina ceramic-filler replaced by the silica ceramic-filler on this composite. Then the X-ray diffraction analysis revealed that the alumina and silica fillers existed as the crystal phase, and the densification was seriously damaged when the silica content reached to three quarters of the fillers. With the increase of the silica-filler, the composites’ density and dielectric constant exhibited uniform decrease, but thermal expansion coefficient (TEC) uniformly increased. When the glass:alumina:silica was equal to 60:30:10, a best composite property was presented as a bulk density of 2.582 (g cm^?1), a dielectric constant of 6.1 and a dielectric loss of 2 × 10^?3 at 1 MHz, a flexural strength of 168 MPa, and a TEC of 8.62 × 10^?6 °C^?1.     

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.