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1.
Polycrystalline samples of Ba4Ln2Fe2Ta8O30 (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10−3 and 2.8 × 10−3 (at 1 MHz) for Ba4La2Fe2Ta8O30 and Ba4Nd2Fe2Ta8O30, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.  相似文献   

2.
New solid solutions, Bi2?x?y Tm x Nb y O3+δ, with tetragonal and cubic structures have been synthesized in the Bi2O3-Tm2O3-Nb2O5 system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi1.8Tm0.15Nb0.05O3+δ is comparable to that of Bi1.75Tm0.25O3, the best conductor in the Bi2O3-Tm2O3 system.  相似文献   

3.
The phase equilibria in the ternary system La2O3-Nb2O5-Nb have been studied at subsolidus temperatures in vacuum (6.65 × 10?3 Pa), and the temperature stability limits of LaNb7O12 have been determined in vacuum and during heating in air.  相似文献   

4.
The study of electrical conductivity of 30Li2O: (70 − x) B2O3: xV2O5 glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V2O5. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.  相似文献   

5.
We have studied general trends of crystallization from high-temperature solutions in the K2O-P2O5-V2O5-Bi2O3 system at P/V = 0.5?2.0, K/(P + V) = 0.7?1.4, and Bi2O3 contents from 25 to 50 wt % and identified the stability regions of BiPO4, K3Bi5(PO4)6, K2Bi3O(PO4)3, and K3Bi2(PO4)3 ? x (VO4) x (x = 0?3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C 2/c): K3Bi2(PO4)2(VO4), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K3Bi2(PO4)1.25(VO4)1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.  相似文献   

6.
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.  相似文献   

7.
Reactions of vanadium, niobium, and tantalum pentoxides with aluminum nitride have been studied using X-ray diffraction. At temperatures from 1000 to 1600°C, we have identified various V, Nb, and Ta nitrides. The composition of the niobium and tantalum nitrides depends on the reaction temperature. The tendency toward nitride formation becomes stronger in the order V2O5 < Ta2O5 < Nb2O5.  相似文献   

8.
The Tm2O3-Rh2O3 system has been studied by x-ray diffraction, thermal analysis, and chemical analysis of annealed and quenched samples. The results have been used to construct a schematic subsolidus phase diagram of the system. Only one double oxide, TmRhO3, has been identified. Some of its physicochemical properties are reported.  相似文献   

9.
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.  相似文献   

10.
We have prepared and characterized lithium titanate-based anode materials, Li4Ti5O12/C and Li4Ti5O12/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li4Ti5O12-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.  相似文献   

11.
The physicochemical properties of BaO-Bi2O3-B2O3 glasses have been studied. The effect of KBF4 additions on the properties of the glasses has been examined. The transmission of the glasses has been correlated with their local structure and composition.  相似文献   

12.
The electrical properties of layered perovskite-like compounds with the general formula Bi m + 1Fe m − 3Ti3O3m + 3 have been studied in relation to their physicochemical properties and structure.  相似文献   

13.
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, Li5?x La3Ta2O12?x (OH) x (0<x<2.15), and the resultant Li2O may react further with water to form LiOH·H2O.  相似文献   

14.
Anisometric and agglomerate-free template particles are important for fabrication of grain-oriented ceramics. In the present work, preparation of acicular KSr2Nb5O15 (KSN) particles was firstly explored in the SrNb2O6–Nb2O5–KCl system by molten salt synthesis (MSS) method. It was found that the molar ratio of SrNb2O6 to Nb2O5, the amount of KCl salt and synthesis time could significantly affect the phase structure and morphology of KSN particles. When calcined at 1,150 °C for 6 h with the molar ratio of SrNb2O6 to Nb2O5 was 1 and the weight ratio of salt to oxide source was 1.50, pure KSN particles with well-developed acicular morphology were successfully obtained in this system. They were agglomerate-free and with proper scale in the size range of 5–30 μm, which made them the ideal templates for fabricating textured ceramics. In addition, some new reaction and growth mechanisms were proposed in this work.  相似文献   

15.
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 Li4/3−x Mn5/3+x O4 composition rather than a single spinel phase with Li in tetrahedral and Li1/3Mn5/3 in octahedral spinel sites. The annealing of Li4Mn5O12 at temperature higher than 600 °C leads to its decomposition into monoclinic Li2MnO3 and spinel Li4/3−x Mn5/3+x O4.  相似文献   

16.
17.
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.  相似文献   

18.
We examine the behavior of the Mo-W-Al2O3 system at T = 2400 K and p = 100 Pa and identify the main chemical reactions that lead to the oxidation of Mo and W. The results indicate that, under these thermodynamic conditions, direct reaction between Mo, W, and molten Al2O3 is impossible, and oxidation processes are indirect and involve vapor species. For a Mo: W: Al2O3 molar ratio of 1: 1: 1, we calculate the gas-phase composition and demonstrate that the predominant vapor species are Al, AlO, Al2O, MoO, MoO2, and WO3.  相似文献   

19.
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.  相似文献   

20.
The Dy2O3-Rh2O3 system is studied by thermal analysis, x-ray diffraction, and chemical analysis of annealed and quenched samples. The results are used to construct a schematic subsolidus phase diagram of the system. Only one double oxide, DyRhO3, is obtained. Some of its physicochemical properties are reported.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 960–965.Original Russian Text Copyright © 2005 by Skrobot, Ugolkov, Grebenshchikov, Gusarov.  相似文献   

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