Dielectric behavior and energy storage properties in BaO–SrO–Nb2O5–B2O3 system glass–ceramics with Gd2O3 addition

A series of strontium barium niobate-based borate system glass–ceramics with Gd₂O₃ addition have been prepared by controlled crystallization method. The effect of Gd₂O₃ addition on the microstructure, phase evolution and dielectric properties has been investigated. The results show that the addition of Gd₂O₃ to the glass–ceramics changes the dielectric property and energy-storage density. Typically, the glass–ceramics with 0.5 mol% Gd₂O₃ heat treated at 630 °C/2 h + 800 °C/3 h possesses a dielectric constant of 136, a breakdown strength of 1,075 kV/mm and energy-storage density of 6.94 J/cm³, which is suitable for the application in high energy-storage capacitors.     

Structural and spectroscopic effects of Ag–Eu3+ codoping of TeO2–PbO glass ceramics

Structural and spectroscopic behavior of TeO₂–PbO–Eu₂O₃ glass ceramics containing small amounts of Ag₂O (0.5 mol%) or metallic Ag nanoparticles (AgNPs) (0.33 mol%) have been studied by varying their Eu₂O₃ content (0–10 mol%). The structural behavior of these samples was investigated by means of X-ray diffraction (XRD), SEM microscopy, and Fourier transform infrared (FTIR) spectroscopy. The average unit-cell parameters, crystallites size, and the quantitative ratio of the crystallographic phases in the samples were evaluated based on XRD data. FTIR spectroscopy data revealed that the TeO₃ and TeO₄ are the main structural units of these glass ceramics and their ratio, TeO₃/TeO₄, changes as function of the europium oxide content and the codoping of the samples. Luminescence spectroscopy measurements evidenced the important peaks located at 438, 550, and 722 nm due to the Pb²⁺ ions and at 589 and 611 nm due to the Eu³⁺ ions present in the studied samples. The presence of AgNPs in the studied glass ceramics determines a considerable enhancement of the luminescence bands of Eu³⁺ ions from 589 and 611 nm.     

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...     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Photoluminescence and scintillation properties of Al(PO3)3–CsPO3–CsBr–CeBr3 glass scintillators

Scintillators, which are widely used as radiation detectors, are phosphors that release absorbed ionizing radiation energy as ultraviolet or visible light. Inorganic glass scintillators have several advantages over inorganic crystal scintillators, such as ease of fabrication and low costs. However, unlike inorganic crystals, which can emit up to tens of thousands of photons/MeV, inorganic glasses exhibit less than several hundred photons/MeV in most cases. Here, we studied an inorganic glass scintillator that exhibits a light yield of 2700 photons/MeV, which exceeds those of previous inorganic glass scintillators with high light yields of approximately 2000 photons/MeV. The density of this material is 3.28 g/cm³, which is relatively high among glass scintillators. Moreover, a fast scintillation decay with a decay time constant of 30.0 ns was obtained and is attributed to the 5d–4f transition of Ce³⁺. Thus, this glass is suitable for gamma- and X-ray detection, thereby expanding the practical applicability of inorganic glass scintillators.

     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

Varistor properties and microstructure of ZnO–BaO ceramics

Ceramics in the system ZnO–BaO have been investigated for possible use as varistors. Specimens were prepared by the mixed oxide route, and were sintered at temperatures in the range 1000–1400°C. The electrical properties were determined using d.c. A and impulse techniques. The ZnO–BaO ceramics have a two-phase microstructure comprising a ZnO phase and a Ba-rich grain boundary phase. Due to liquid phase sintering, the average grain sizes for the ZnO–BaO ceramics are large (typically 35–55 m for samples sintered at 1300°C). This results in low breakdown fields, (1000 V cm-1). The maximum non-linearity exponent obtained for ZnO–BaO ceramics (14) is higher than that for binary ZnO–Bi2O3 ceramics. However, the high water solubility of the Ba-rich phase may restrict the use of ZnO–BaO ceramics.     

Improved microwave dielectric properties of Mg4Nb2O9 ceramics with CaO–B2O3–SiO2 glass additions

The effects of CaO–B₂O₃–SiO₂ (CBS) glass addition on the sintering temperature and dielectric properties of Mg₄Nb₂O₉ ceramics have been investigated using X-ray diffraction, Scanning electron microscopy and Differential thermal analysis. The CBS glass can change to liquid phase at about 750 °C and a small amount of CBS glass addition to Mg₄Nb₂O₉ ceramics can greatly decrease the sintering temperature to about 1,125 °C. It is revealed that the reduced sintering temperature is attributed to the formation of liquid phase. The major phases of the sample are Mg₄Nb₂O₉ and MgNb₂O₆. The relationship between τ _f values and the content of glass additions have the reverse change trends. The Mg₄Nb₂O₉ ceramics with 2wt% glass addition sintered 1,125 °C exhibit good microwave dielectric properties: dielectric constant (ε _r ) of 13 and Q·f value of 69,000 GHz.     

Spectroscopic properties of Eu3+/Nd3+ co-doped phosphate glasses and opaque glass–ceramics

This paper reports the fabrication and characterization of Eu³⁺/Nd³⁺ co-doped phosphate (PNE) glasses and glass–ceramics as a function of Eu³⁺ concentration. The precursor glasses were prepared by the conventional melt quenching technique and the opaque glass–ceramics were obtained by heating the precursor glasses at 450 °C for 30 h. The structural and optical properties of the glass and glass–ceramics were analyzed by means of X-ray diffraction, Raman spectroscopy, UV–VIS–IR absorption spectroscopy, photoluminescence spectra and lifetimes. The amorphous and crystalline structures of the precursor glass and opaque glass–ceramic were confirmed by X-ray diffraction respectively. The Raman spectra showed that the maximum phonon energy decreased from 1317 cm⁻¹ to 1277 cm⁻¹ with the thermal treatment. The luminescence spectra of the glass and glass–ceramic samples were studied under 396 nm and 806 nm excitation. The emission intensity of the bands observed in opaque glass–ceramic is stronger than that of the precursor glass. The luminescence spectra show strong dependence on the Eu³⁺ ion concentration in the Nd³⁺ ion photoluminescence (PL) intensity, which suggest the presence of energy transfer (ET) and cross-relaxation (CR) processes. The lifetimes of the ⁴F_3/2 state of Nd³⁺ ion in Eu³⁺/Nd³⁺ co-doped phosphate glasses and glass–ceramics under 806 nm excitation were measured. It was observed that the lifetimes of the ⁴F_3/2 level of Nd³⁺ of both glasses and glass–ceramics decrease with the increasing Eu³⁺ concentration. However in the case of opaque glass–ceramics the lifetimes decrease only 16%.     

Microwave synthesis and properties of NaPO3–SnO–Nb2O5 glasses

Tin niobiophosphate glasses were produced using a domestic microwave oven under a nitrogen flow. The fast microwave melting method and the protective atmosphere prevent the oxidation of SnO. After 10 min of heating, the NaPO₃, SnO, and Nb₂O₅ mixtures are homogeneous and permit to obtain transparent glasses. Three series of glasses with different Sn/Nb ratio were studied to determine the influence of each oxide. The glass transition temperature increases linearly with the amount of Nb₂O₅ and SnO. These variations are more important for compositions with high metallic cation proportions and with a low Sn/Nb ratio. The same evolutions were observed for the density, Vickers hardness, and elastic modulus while the thermal expansion coefficient decreases monotonously. The simultaneous insertion of SnO and Nb₂O₅ in phosphate glass matrix leads to a progressive strengthening of the glass network. The chemical durability of the glasses also increases as a function of the amount of metal oxides. We prepared a bulk glass sample with a dissolution rate of about 3.3 × 10⁻⁸ g cm⁻² min⁻¹ in renewed water conditions at 95 °C. This durability is equivalent to those of the window glass whereas the glass transition temperature remains lower than 485 °C.     

Effect of sintering process on electrical properties and ageing behavior of ZnO–V2O5–MnO2–Nb2O5 varistor ceramics

The effect of sintering process on microstructure, electrical properties, and ageing behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅ (ZVMN) varistor ceramics was investigated at 875–950 °C. The sintered density decreased from 5.52 to 5.44 g/cm³ and the average grain size increased from 4.4 to 9.6 μm with the increase of sintering temperature. The breakdown field (E_{1 mA}) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 °C led to surprisingly high nonlinear coefficient (α = 50). The donor concentration (N_d) increased from 3.33 × 10¹⁷ cm⁻³ to 7.64 × 10¹⁷ cm⁻³ with the increase of sintering temperature and the barrier height (Φ_b) exhibited the maximum value (1.07 eV) at 900 °C. Concerning stability, the varistors sintered at 925 °C exhibited the most stable accelerated ageing characteristics, with %ΔE_{1 mA} = 1.5% and %Δα = 13.3% for DC accelerated ageing stress of 0.85 E_{1 mA}/85 °C/24 h.     

New high permittivity and low loss ceramics in the BaO–TiO2–Nb2O5 composition

New dielectric ceramics with formula BaTi3Nb4O17 and Ba6Ti14Nb2O39 have been prepared and characterized. BaTi3Nb4O17 was densified to 92% of TD after firing at 1310 °C for 4 h. However, Ba6Ti14Nb2O39 fired under optimized conditions (1260 °C for 4 h) showed only 85% TD together with secondary phase. The crystal system of both of the compositions is orthorhombic. The BaTi3Nb4O17 has r56, Qu2100 (at 4.402 GHz), f+86 p.p.m. K-1 and Ba6Ti14Nb2O39 as r50, Qu650 (4.359 GHz) and f+165 p.p.m. K-1. © 1998 Kluwer Academic Publishers     

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.     

Characterization of SiO2–Na2O–Fe2O 3–CaO–P2O 5–B 2O 3 glass ceramics

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO₂–Na₂O–Fe₂O₃–CaO–P₂O₅–B₂O₃ system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na₃CaSi₃O₈ and Na_3-XFe_XPO₄ phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.