Low-firing Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript> microwave dielectric ceramics with BaCu(B<Subscript>2</Subscript>O<Subscript>5</Subscript>) additive

Phase purity, microstructure, sinterability and microwave dielectric properties of BaCu(B₂O₅)-added Li₂ZnTi₃O₈ ceramics and their cofireability with Ag electrode were investigated. A small amount of BaCu (B₂O₅) can effectively reduce the sintering temperature from 1075°C to 925°C, and it does not induce much degradation of the microwave dielectric properties. Microwave dielectric properties of ε _r = 23·1, Q × f = 22,732 GHz and τ _f = − 17·6 ppm/°C were obtained for Li₂ZnTi₃O₈ ceramic with 1·5 wt% BaCu(B₂O₅) sintered at 925°C for 4 h. The Li₂ZnTi₃O₈ +BCB ceramics can be compatible with Ag electrode, which makes it a promising microwave dielectric material for low-temperature co-fired ceramic technology application.     

Investigation of Li<Subscript>2</Subscript>Zn<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>-based temperature stable dielectric ceramics for LTCC applications

A low temperature co-fired ceramic (LTCC) was fabricated at 910 °C /2 h from the powder mixture of Li₂Zn₃Ti₄O₁₂, TiO₂ and a B₂O₃–La₂O₃–MgO–TiO₂ glass (BLMT), and the influence of TiO₂ on microstructure and dielectric properties of the composite was investigated in the composition range (wt%) of 20BLMT–(80???x)Li₂Zn₃Ti₄O₁₂–xTiO₂ (x?=?0, 2.5, 5, 7.5, 9 and 10). The results showed that all samples consisted of Li₂Zn₃Ti₄O₁₂, TiO₂, LaBO₃ and LaMgB₅O₁₀ phase. And LaBO₃, LaMgB₅O₁₀ and a small amounts of TiO₂ were crystallized from BLMT glass during sintering process. As x increases, dielectric constant and temperature coefficient of resonance frequency of the composites demonstrated gradually increase, whereas the quality factor of the sample of x?=?0 wt% was about 41,500 GHz and the ones maintained stable at a high level of 49,000–51,000 GHz for other samples. The composite with x?=?9 wt% had an optimal microwave dielectric properties with the dielectric constant of 20.2, quality factor of 50,000 GHz and temperature coefficient of resonant frequency of ??0.33 ppm/°C.     

Preparation of magnetic composites through SrO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass crystallization

Glasses with nominal compositions 11SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (1) and 15SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.     

Electric-field effect on crystal growth in the Li<Subscript>3</Subscript>PO<Subscript>4</Subscript>-Li<Subscript>4</Subscript>GeO<Subscript>4</Subscript>-Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-LiF system

We have studied the electric-field effect on crystallization processes in the Li₃PO₄-Li₄GeO₄-Li₂MoO₄-LiF system. In zero field, Li_3+x P_1?x Ge _x O₄ (x = 0.31) crystals were grown on the cathode under the conditions of this study. At low applied voltages (≤ 0.5 V), we obtained Li₂MoO₄, Li₂GeO₃, and Li_1.3Mo₃O₈. In the range V = 0.5–1 V, crystals of Li_3+x P_1?x Ge _x O₄ solid solutions with x = 0.17, 0.25, 0.28, 0.29, and 0.36 were obtained. An applied electric field was shown to reduce the melting temperature of the starting mixtures and the crystallization onset temperature.     

Low temperature preparation of the Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript> ceramics with the addition of BaO and B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The Zn₂SiO₄ ceramics with the addition of BaO and B₂O₃ are fabricated by traditional solid-state preparation process at a sintering temperature of 900 °C. The introduction of BaO and B₂O₃ to the binary system ZnO-SiO₂ is achieved by adding 10 and 20 wt. % flux BB to the mixed ZnO-SiO₂ ceramic powders pre-sintered at 1,100 °C, respectively. The chemical composition of the flux BB (50 wt.%BaO-50 wt.% B₂O₃) is located at a liquid phase zone with a temperature range of about 869–900 °C in the binary diagram BaO-B₂O₃. In addition, the introduction of BaO and B₂O₃ to the binary system ZnO-SiO₂ is also achieved by the means of a chemical combination of H₂SiO₃, H₃BO₃, ZnO and Ba(OH)₂·8H₂O, which can result in the formation of the hydrated barium borates with low melting characteristics. In turn, by the liquid sintering aid of the barium borate melts, the preparation process of the Zn₂SiO₄ ceramics can be further simplified. In the two preparation methods, the Zn₂SiO₄ ceramics with the 1.5–2.0 ZnO/SiO₂ molar ratios and the addition of a 10 wt. % flux BB can show good dielectric properties whereas the bending strength mainly depends on the microstructure of the Zn₂SiO₄ ceramics and SiO₂ content in the composition of the specimen.     

Growth and properties of LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript>-NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript> crystals

Platelike Li_{1 ? x} Na _x Cu₂O₂ single crystals up to 2 × 10 × 10 mm in dimensions have been grown by slowly cooling (1 ? x)Li₂CO₃·xNa₂O₂·4CuO melts in alundum crucibles in air. Li_{1 ? x} Na _x Cu₂O₂ solid solutions in the LiCu₂O₂-NaCu₂O₂ system have been shown to exist in the composition range 0.78 < x < 1. The temperature stability ranges of NaCu₂O₂ and LiCu₂O₂ are 780–930 and 890–1050°C, respectively. The Mössbauer spectra and electrical conductivity of the crystals have been measured.     

Low-temperature sintering and microwave dielectric properties of Mg<Subscript>3</Subscript>B<Subscript>2</Subscript>O<Subscript>6</Subscript>-LMZBS composites

The Mg₃B₂O₆ ceramics with lithium magnesium zinc borosilicate (LMZBS) glass were prepared at a lower sintering temperature. The effects of the glass addition on the densification, phase development, microstructure and microwave dielectric properties of the Mg₃B₂O₆ ceramics were investigated. The addition of LMZBS glass improved the densification and lowered the sintering temperature of Mg₃B₂O₆ ceramics from 1,300 to 950 °C. X-ray diffraction patterns showed that Mg₃B₂O₆ transformed into Mg₂B₂O₅ and a new phase, Li₂ZnSiO₄, crystallized from the glass phase. Because of the high dielectric performance of these phases, Mg₃B₂O₆ mixed with 55 wt% LMZBS sintered at 950 °C for 3 h had ε_r = 6.8, Q × f = 50,000 GHz, and τ_f = ?64 ppm/°C at 7.28 GHz. The chemical compatibility of ceramic-glass composites with Ag was also investigated for LTCC.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Effect of Melt Composition on the Luminescent Properties of Czochralski-Grown Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> Single Crystals

Li₂B₄O₇ (LTB) single crystals are grown from stoichiometric and B₂O₃-enriched (1.6 and 2.4 mol %) melts. At large B₂O₃ excesses, the thermoluminescence intensity in the crystals is markedly higher, attesting to an increased density of structural defects. LTB crystals grown from B₂O₃-enriched melts may contain zones enriched in two types of defects. Defects of one type result from the breaking of bonds involving bridging oxygens, without significant changes in the position of neighboring atoms. Defects of the other type appear at large B₂O₃ excesses in the melt, which enable more significant changes in the structure of the boron-oxygen framework, leading to the formation of nanoscale regions differing in composition from LTB. The present results may be helpful in assessing the quality of LTB single crystals and in optimizing the crystal growth of LTB.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Effects of sodium oleate on synthesis and photocatalytic activity of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>@RGO

In this study, the effects of sodium oleate on synthesis of Bi₂WO₆/Bi₂O₃ loaded reduced graphene oxide photocatalyst was studied. The as-prepared composites were characterized by X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance and photoluminescence spectroscopy. The results suggested that addition of sodium oleate not only promoted synthesis of Bi₂O₃, but also enhanced the reduction of GO to graphene. When the amount of sodium oleate was 4 mol (Bi:SO?=?1:1), Bi₂WO₆/Bi₂O₃@RGO to the best visible-light photocatalytic activity can be synthesized by a facile one-step solvothermal process without further reduction reaction. Hence, it indicated that sodium oleate could affect the synthesis of the as-prepared composites and the photocatalytic activity for degradation of RhB. This study did provide not only a facile method to synthesize Bi₂WO₆/Bi₂O₃@RGO, but also a method to reduce graphene oxide to graphene.     

Low-temperature sintering behavior and properties of <Emphasis Type="Italic">monoclinic</Emphasis>-SrAl<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics prepared via an aqueous suspension milling process

In this work, by an aqueous suspension milling process, boric acid (H₃BO₃), calcium hydroxide [Ca(OH)₂], strontium carbonate (SrCO₃) and barium hydroxide octahydrate [Ba (OH)₂·8H₂O] are mixed with strontium carbonate (SrCO₃) and kaolin (Al₂O₃·2SiO₂·2H₂O) to prepare SrAl₂Si₂O₈ ceramics with a sintering temperature of 950 °C. According to chemical compositions of flux agents B₂O₃, CaO·2B₂O₃, SrO·2B₂O₃ and BaO·2B₂O₃, raw materials boric acid, calcium hydroxide, strontium carbonate and barium hydroxide octahydrate were introduced to the suspension slurries of strontium carbonate and kaolin to decrease the densification sintering temperature of SrAl₂Si₂O₈ ceramics. In addition, the Sr element in SrAl₂Si₂O₈ ceramics are partly substituted with Ba and Ca elements, respectively, to investigate the low-temperature sintering behavior of partly substituted SrAl₂Si₂O₈ ceramics. The results indicated that the addition of flux agents to SrAl₂Si₂O₈ ceramics can availably achieve the densification sintering of SrAl₂Si₂O₈ ceramics at 950 °C, whereas the substitution of Sr with Ca or Ba have a great effect on sintering behaviors and dielectric properties of SrAl₂Si₂O₈ ceramics. Additionally, main crystal phases of the SrAl₂Si₂O₈ ceramics are monoclinic- SrAl₂Si₂O₈ and small quartz, but the evolution of crystal phases also depend on flux agents.     

Synthesis and conductivity studies of Li<Subscript>1.5</Subscript>Al<Subscript>0.5</Subscript>Ge<Subscript>1.5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolyte

This paper describes the preparation of a lithium ion conducting solid electrolyte with the composition Li_1.5Al_0.5Ge_1.5(PO₄)₃ by a new liquid-phase method with the use of the water-soluble salts Al(NO₃)₃ · 9H₂O, LiNO₃ · 3H₂O, and (NH₄)₂HPO₄ and the germano-oxalic acid H₂[Ge(C₂O₄)₃]. The synthesized materials have been characterized by X-ray diffraction, differential scanning calorimetry, thermogravimetry, and impedance spectroscopy. The results demonstrate that sintering of the synthesized amorphous powders at a temperature of 650°C leads to the formation of phase-pure Li_1.5Al_0.5Ge_1.5(PO₄)₃. The ionic conductivity of the electrolyte measured at frequencies from 10 Hz to 2 MHz using pellets with an 86% relative density was 4.2 × 10^–4 S/cm.     

Thermodynamic Properties of FeNb<Subscript>2</Subscript>O<Subscript>6</Subscript> and FeTa<Subscript>2</Subscript>O<Subscript>6</Subscript>

Empirical calculational approaches have been used to evaluate the enthalpy, entropy, heat capacity, and melting point of iron(II) niobate and iron(II) tantalate and the coefficients A, B, and C in an equation for the temperature dependence of their heat capacity. The melting point of FeTa₂O₆ has been experimentally determined to be 1891 ± 5 K. The calculated heat capacity (C°_p (298.15 K)) of iron tantalate and the Gibbs energies of formation of FeN₂O₆ and FeTa₂O₆ have been compared to previously reported data.     

Calcium bismuth borates in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The 600°C (subsolidus) section of the CaO-Bi₂O₃-B₂O₃ phase diagram has been studied by x-ray diffraction and differential thermal analysis. A new calcium bismuth borate of composition CaBi₂B₄O₁₀ has been identified, and the existence of CaBi₂B₂O₇ has been confirmed. According to T-x phase diagram data, these compounds form peritectically at 700±5 and 783±5°C, respectively.     

Phase developments in Pb(Mg<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> and Pb(Zn<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> via B-site precursor route

Phase formation stages of MgWO₄ and ZnWO₄ (precursor compositions for following steps) were investigated by monitoring the reactions of oxide chemicals at various temperatures. Developed phases were examined by using X-ray diffraction (XRD). Successive attempts were also conducted for Pb(Mg_1/2W_1/2)O₃ (PMW) and Pb(Zn_1/2W_1/2)O₃ (PZW) by reacting PbO with the precursor compounds. Stages of phase development in the two compositions were also analyzed. The results are compared with those of another tungsten-containing perovskite Pb(Fe_2/3W_1/3)O₃ (PFW) and its B-site precursor Fe₂WO₆. After PbO addition to the precursor powders, a perovskite phase formed directly (i.e., without any intermediate phases) in the case of PMW. For PbO + ½ZnWO₄, in contrast, the decomposition of ZnWO₄ and preferential reaction with PbO resulted in Pb₂WO₅ and ZnO, instead of the perovskite PZW.     

Effect of impurities on the electrical properties of the defect perovskite Li<Subscript>0.33</Subscript>La<Subscript>0.57</Subscript>TiO<Subscript>3</Subscript>

A perovskite phase with the composition Li_0.33La_0.57TiO₃ modified with up to 7 wt % Bi₂O₃, SiO₂, Li₃PO₄, or Li₃BO₃ has been prepared by solid-state reactions. The samples in the LLTO–Li₃PO₄, LLTO–Bi₂O₃, and LLTO–SiO₂ systems were single-phase over the entire composition range studied. In the LLTO–Li₃BO₃ system, increasing the lithium borate concentration causes a transition from a defect perovskite structure to the layered perovskite-related structure of Li₂La₂Ti₃O₁₀. The addition of Bi₂O₃ and Li₃PO₄ has been shown to increase the total conductivity of the ceramics by almost one order of magnitude. Li₃BO₃, Li₃PO₄, Bi₂O₃, and SiO₂ additives improve the sintering behavior of the Li_0.33La_0.57TiO₃ ceramics.     

Investigation on the stability of Li<Subscript>5</Subscript>La<Subscript>3</Subscript>Ta<Subscript>2</Subscript>O<Subscript>12</Subscript> lithium ionic conductors in humid environment

In this paper, the stability in humid air of Li₅La₃Ta₂O₁₂ lithium ionic conductors synthesized by conventional solid-state reaction was investigated by internal friction, conductivity, weight variation, X-ray diffraction, and thermogravimetric analysis methods. It was found that when the Li₅La₃Ta₂O₁₂ samples were aged in open air at room temperature, the internal friction peaks associated with the short-distance diffusion of lithium vacancies gradually shift toward higher temperature and increase in height, while the weight of the sample increases and impurity phases of LiOH·H₂O appear. These results reveal that the Li₅La₃Ta₂O₁₂ compounds are unstable against moisture in open air at room temperature. It was suggested that the protons from the moisture substitute the lithium ions in Li₅La₃Ta₂O₁₂ samples to form Li₂O and new protonic derivatives, Li_5?x La₃Ta₂O_12?x (OH) _x (0<x<2.15), and the resultant Li₂O may react further with water to form LiOH·H₂O.     

Thermodynamic properties of SrAl<Subscript>12</Subscript>O<Subscript>19</Subscript> and SrAl<Subscript>4</Subscript>O<Subscript>7</Subscript>

Strontium aluminates are important compounds with interesting properties such as long-duration phosphorescence and elastico-deformation luminescence. They have potential application in flexible light emitting panels. Since there are serious discrepancies in available thermodynamic data for these compounds, a redetermination of their Gibbs energies of formation was undertaken using solid-state electrochemical cells incorporating single-crystal SrF₂ as the electrolyte in the temperature range from 1000 to 1300 K. However, the measurements were restricted to SrAl₁₂O₁₉ and SrAl₄O₇ because of the formation of strontium oxyfluoride phase between SrAl₂O₄ and SrF₂. For the reactions, SrO + 6 Al₂O₃ → SrAl₁₂O₁₉, ΔG ^o/J mol^?1 (± 280) = ?83386 ? 25.744 (T/K), and SrO + 2Al₂O₃ → SrAl₄O₇, ΔG ^o/J mol^?1 (± 240) = ?80187 ? 25.376 (T/K). The high entropy of SrAl₄O₇ and SrAl₁₂O₁₉ can be partly related to their complex structures. The results of this study are consistent with calorimetric data on enthalpy of formation of other Sr-rich aluminates and indicate only marginal stability for SrAl₄O₇ relative to its neighbours, SrAl₁₂O₁₉ and SrAl₂O₄. The thermodynamic data explain the difficulty in direct synthesis of phase pure SrAl₄O₇ and the formation of SrAl₂O₄ as the initial ternary phase when reacting SrO and Al₂O₃ or crystallizing from amorphous state, irrespective of composition.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years