BaO—TiO2系中Ba2Ti9O20相形成的研究

研究了ＡａＯ－ＴｉＯ２系中Ｂａ２Ｔｉ９Ｏ２０相的形成规律。结果表明：ＢａＯ－ＴｉＯ２系中，不加任何添加剂可以合成Ｂａ２Ｔｉ９Ｏ２０相；在ＢａＯ－ＴｉＯ２系中Ｂａ；Ｔｉ＝２：９附近存在一个很窄的单相Ｂａ２Ｔｉ９Ｏ２０区；烧结阶段Ｂａ２Ｔｉ９Ｏ２０相的最终合成并不依赖于预烧阶段部分此相的形成。     

Synthesis and Study of Isomorphous Miscibility Limits of Crystalline Phases with a Hollandite-Type Tunnel Structure in the Cs2O(MeO)–Al2O3–TiO2 (Me = Ba, Sr) Systems*

The possibility of forming hollandite-type phases during the solid-phase reaction in the Cs₂O(MeO)–Al₂O₃–TiO₂ (Me = Ba, Sr) systems is studied. It is revealed that, in the Cs₂O–BaO–Al₂O₃–TiO₂ system, the region of existence of Cs _x Ba_{1 – x/2}Al₂Ti₅O₁₄ solid solutions with a hollandite-type structure lies in the concentration range 0 x 0.7. In the SrO–BaO–Al₂O₃–TiO₂ system, no solid solutions with a hollandite-type structure are observed. The mechanism and kinetics of formation of the Cs _x Ba_{1 – x/2}Al₂Ti₅O₁₄ (0 x 0.7) solid solutions are analyzed, and the optimum conditions for synthesis of these solutions are determined.     

Preparation of PTCR ceramics in the BaO–Nb2O5–TiO2 system

The PTCR effect was investigated in the ferroelectric BaNb₂O₆ phase doped with TiO₂. Composite ceramics formed after sintering in a reducing atmosphere and subsequent reoxidation show the PTCR effect at around 70 and 300°C, respectively. Both PTCR anomalies are associated with the formation of high resistivity grain boundaries after controlled oxidation of reduced constituent phases.     

Effects of BaO–SiO2 glass particle size on the microstructures and dielectric properties of Mn-doped Ba(Ti,Zr)O3 ceramics

The sintering behavior, microstructures and dielectric properties of Mn-doped Ba(Ti, Zr)O₃ (BTZ) ceramics with different particle sizes of BaO–SiO₂ glass (D50 ranging between 185 and 1200 nm) were investigated. From the metallographic observation, adding finer glass frit revealed more homogeneous compositional distribution. It was found that better spreading of the glass phase could be achieved by adding finer glass particles that could penetrate the BTZ ceramic interface more easily, thus enhancing the grain growth. The extent of the incorporation between glass and ceramic increased with smaller glass particles, and the Curie temperature was altered accordingly. Microstructural evaluation conducted by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) with an energy-dispersive X-ray spectrometer (EDS) indicated the glass particle size has a dramatic influence on the sintering behavior and microstructure of Mn-doped BTZ ceramics. The relationship between microstructures and dielectric properties was also discussed in this study.     

Fabrication of lead-free Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 nanoparticles and the application in flexible piezoelectric nanogenerator

Recently, flexible nanogenerators have attracted much attention due to the continuous demand of portable electronic devices. Thus, in our present work, a flexible piezoelectric nanogenerator (pNG) was fabricated by mixing 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ nanoparticles (BCTZ NPs) and a PDMS polymer matrix. The flexible device exhibited excellent performance with maximum open-circuit voltage of 0.6 V and short-circuit current of 7.5 nA. BCTZ NPs were prepared by a reaction between a metallic salt and a metallic oxide in a solution of composite-hydroxide eutectic. XRD pattern showed BCTZ NPs to have pure perovskite structure. In this paper, the structure, morphology of the BCTZ NPs, and electric property of the BCTZ-based pNG were systematically studied. With the advantages of small-size, environmentally friendly, high flexibility, and high-sensitivity to external vibration, BCTZ will open up a range of new applications.     

Microwave dielectric properties of LTCC materials consisting of glass–Ba2Ti9O20 composites

Interaction between Ba₂Ti₉O₂₀ microwave dielectric ceramics and BaBSiO glass materials was systematically investigated. BaTi(BO₃)₂ intermediate phase was induced and its proportion increased with firing temperature. Fortunately, the formed BaTi(BO₃)₂ phase does not result in marked degradation on the microwave dielectric properties of the Ba₂Ti₉O₂₀–BaBSiO composite materials. Good microwave dielectric properties (K=13.2, Q×F=1150) were obtained by firing the Ba₂Ti₉O₂₀–BaBSiO (50:50 vol.%) materials at 900 °C for 30 min. Precoating a thin layer of BaTi(BO₃)₂ materials on the Ba₂Ti₉O₂₀ powders prior to processing of the ceramic tapes can markedly suppress the interaction between the Ba₂Ti₉O₂₀ and BaBSiO glass, significantly improving the consistency of the microwave dielectric properties for the low temperature cofirable ceramic (LTCC) materials.     

Dielectric Characteristics of Ceramics in BaO–Nd2O3–TiO2–Ta2O5 System

Dielectric ceramics in the BaO–Nd₂O₃–TiO₂–Ta₂O₅ system were prepared and characterized. The ceramics with tungsten–bronze structure based on the compositions Ba₂NdTi₂Ta₃O₁₅ and Ba₅NdTi₃Ta₇O₃₀ had a high dielectric constant (>100) with a lower frequency-dependency when complete densification was achieved; a low dielectric loss was obtained in the former.     

High permittivity and low loss dielectric ceramics in the BaO–La2O3–TiO2–Ta2O5 system

Dielectric ceramics were synthesized and characterized in the BaO–La₂O₃–TiO₂–Ta₂O₅ quaternary system for the three typical compositions: Ba₃La₃Ti₅Ta₅O₃₀, Ba₄La₂Ti₄Ta₆O₃₀ and Ba₅LaTi₃Ta₇O₃₀, which formed the filled tungsten-bronze structures. The present ceramics indicated high dielectric constant ε (127.7–148.1) and low dielectric loss tanδ (in the order of 10⁻⁴–10⁻³ at 1 MHz). Meanwhile, the temperature coefficient of dielectric constant τ_ε varied from −728 to −1347 ppm/°C with increasing Ba and Ta and decreasing La and Ti concentration in the temperature range of 20–85 °C. The present ceramics are promising candidates for high-ε and low loss dielectric ceramics, and the suppression of τ_ε should be the primary issue in the future work.     

Processing mediated enhancement of ferroelectric and electrocaloric properties in Ba(Ti0.8Zr0.2)O3–(Ba0.7Ca0.3)TiO3 lead-free piezoelectrics

High-performance Ba(Ti_0.8Zr_0.2)O₃–(Ba_0.7Ca_0.3)TiO₃ (BCZT) fiber crystals were grown using laser-heated pedestal growth (LHPG) for a systematic investigation of processing effects on structure and physical properties. By changing the growth rate (200−5 mm/h), fiber crystals with varying stoichiometry were realized: controlled composition, Ba_0.872Ca_0.128Ti_0.925Zr_0.075O_3-δ, for the optimized crystal (5 mm/h), relative to the ceramic sample (SS) synthesized by the ceramic method. SS and optimized fibers exhibited larger energy storage densities of 700 and 868 mJ/cm³, respectively. Electrocaloric (EC) measurements by direct and indirect methods yielded ΔT of 1.3 K & 0.95 K and EC responsivity (ΔT/ΔE) of 0.3 and 0.43 K mm/kV for SS and 5 mm/h respectively, at 30 kV/cm, at least two-folds higher compared to 200 mm/h fiber. The EC responsivity of our samples is comparable to that of Pb(Mg,Nb)O₃ crystals. These results demonstrate that BCZT has potential application as EC elements when the composition is controlled by fine-tuning of growth parameters.     

Phase equilibria and stability of intermediate phases in the Sm2O3–BaO–Fe2O3 system

Phase equilibria in the ½ Sm₂O₃–BaO–½ Fe₂O₃ system were systematically studied at 1100°C in air. Two individual compounds: Sm_1.875Ba_3.125Fe₅O_15-δ and Ba₃SmFe₂O_7.5+δ have been detected in the studied system at 1100°C in air. One more complex oxide with double perovskite structure SmBaFe₂O_5+w has been obtained under reduced oxygen partial pressure. Thermodynamic stability of SmBaFe₂O_5+w and its thermal stability in metastable state in air were determined. The subsolidus phase diagram for the ½ Sm₂O₃ – BaO – ½ Fe₂O₃ system at 1100°C in air has been constructed.     

Strong photoluminescence and piezoelectricity properties in Pr-doped Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 ceramics: Influence of concentration and microstructure

(Ba_0.85Ca_0.15)_1−xPr_x(Zr_0.1Ti_0.9)O₃ (where 0 < x < 0.01, abbreviated as BCZT:xPr) ceramics were fabricated by conventional solid-state reaction method. The influence of dopant concentration and microstructure on photoluminescence, ferroelectric, and piezoelectric properties was systematically investigated. The results showed that the photoluminescence spectra of the samples exhibited strong green (530 nm) and red (602 nm) emissions upon excitation of the 430 nm to 500 nm light, which couples well with to the emission band of the commercial blue light-emitting diodes chips. The emission intensities were strongly dependent on the dopant concentration and crystallite size, which reached the optimal value when the crystallite size and dopant concentration were 8 μm and 0.002 mol, respectively. Meanwhile, a large piezoelectric response with d₃₃ = 325 pC/N was obtained for BCZT:0.002Pr near the morphotropic phase boundary. Therefore, the Pr-doped BCZT materials, simultaneously exhibiting excellent luminescent properties and high piezoelectric properties, may have significant technological promise in novel multifunctional devices.     

Effect of in situ formation of Ti(C,N) on the properties of Al2O3–ZrO2–C slide plate material

Al₂O₃–ZrO₂–C slide plate was ordinarily used in sliding nozzle system because of its excellent mechanical properties and slag corrosion resistance. This study improved the slag corrosion resistance of the slide plate by the carbothermic reduction of TiO₂ and aluminothermic reduction of TiO₂ under high temperature in coke bed to generate Ti(C,N) phase in situ. The result revealed that TiC of the high melting point phase could enter into anorthite (CaAl₂Si₂O₈) of the low melting point phase, forming eutectic phase CaAl₂Si₂O₈–TiC, and improve the viscosity of the slag. Furthermore, TiC and CaAl₂Si₂O₈ captured FeO and MnO from the slag, resulting in the increase of the slag viscosity, inhibiting the penetration corrosion of the slag, and improving the slag corrosion resistance of the materials. In general, compared with the material without TiO₂ powder, the slag corrosion resistance of the material introduced 2 wt.% TiO₂ powder was increased by 24%. Meanwhile, the cold crushing strength of fired specimen at room temperature was increased by 35.6%.     

Citrate-Nitrate Synthesis and the Electrophysical Properties of Ceramics in the K2O–TiO2–Fe2O3 System

Glass Physics and Chemistry - This paper presents a study of the electrically conductive properties of ceramics based on phases crystallizing in the K2O–Fe2O3–TiO2 system, when using...     

Relationship Between the Synthesis and Structure of Ceramic Precursors of the TiO2–CeO2–ZrO2 System

Refractories and Industrial Ceramics - Tetragonal solid solutions based on the TiO2–CeO2–ZrO2 system stable up to 1,350°C were obtained. A method of pH titration of the initial...     

Heat-Insulating Properties of High-Alumina Materials Filament-Reinforced with Glass Fiber of the Al2O3–SiO2 and Al2O3–SiO2–ZrO2 Systems

Refractories and Industrial Ceramics - Refractory heat-insulating materials produced in Russia are characterized. The thermal stability of high-alumina heat-insulating materials filament-reinforced...     

Thermal conductivity of single- and multi-phase compositions in the ZrO2–Y2O3–Ta2O5 system

Compositions in the ZrO₂–Y₂O₃–Ta₂O₅ system are of interest as low thermal conductivity, fracture resistant oxides for the next generation thermal barrier coatings (TBC). Multiple phases occur in the system offering the opportunity to compare the thermal properties of single, two-phase, and three-phase materials. Despite rather large variations in compositions almost all the solid solution compounds had rather similar thermal conductivities and, furthermore, exhibited only relatively small variations with temperature up to 1000 °C. These characteristics are attributed to the extensive mass disorder in all the compounds and, in turn, small interfacial Kapitza (thermal) resistances. More complicated behavior, associated with the transformation from the tetragonal to monoclinic phase, occurs on long-term annealing in air of some of the compositions. However, the phases in two of the compositional regions do not change with annealing in air and their thermal conductivities remain unchanged suggesting they may be suitable for further exploration as thermally stable TBC overcoats.     

Glass Formation and Properties of Glasses in the PbO–ZnO–B2O3System

Glasses in the PbO–ZnO–B₂O₃system with a lead oxide content of less than 65 mol % are studied. The glass formation region for these glasses is determined. Their crystallization ability, density, and moisture resistance and the thermal, optical, and electrical properties are investigated. The composition–property curves are constructed. It is found that these dependences exhibit anomalies for glasses along the composition joins with constant boron oxide contents of 40 and 50 mol %. These anomalies can be associated with the change in the role of lead ions in the glass structure.