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1.
Bi5Ti3FeO15 (BTF) is an example of bifferoic Aurivillius phase with perovskite layered structure. Materials on the basis BTF are of substantial interest for new types of magnetoelectric device applications. In this review we discuss technology of preparation biferroic ceramic with composition Bi5Ti3FeO15. The ferroelectric layered Bi5Ti3FeO15 (BTF) Aurivillius phases were synthesized by solid-phase synthesis reaction from the conventional mixture of oxides, viz. Bi2O3, Fe2O3, TiO2. Thermal analysis and mass change efect were used to investigate synthesis effects in the stoichiometric mixture of powders. The crystalline structure was checked by X-ray diffraction method at room temperature. Microstructure was investigated by scanning electron microscopy.  相似文献   

2.
In this work, a one-step solid-phase sintering process via TiO2 and Li2CO3 under an argon atmosphere, with ultra-fine titanium powder as the modifying agent, was used to prepare a nano-sized Li4Ti5O12/Ti composite (denoted as LTO–Ti) at 800 °C. The introduction of ultra-fine metal titanium powder played an important role. First, X-ray photoelectron spectroscopy demonstrates that Ti4+ was partially changed into Ti3+, through the reduction of the ultra-fine metal titanium powder. Second, X-ray diffraction revealed that the ultra-fine metal titanium powder did not react with the bulk structure of Li4Ti5O12, while some pure titanium peaks could be seen. Additionally, the size of LTO–Ti particles could be significantly reduced from micro-scale to nano-scale. The structure and morphology of LTO–Ti were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical tests showed a charge/discharge current of 0.5, 1, 5, and 10 C; the discharge capacity of the LTO–Ti electrode was 170, 161, 140, and 111 mAh g?1. It is believed that the designed LTO–Ti composite makes full use of both components, thus offering a large contact area between the electrolyte and electrode, high electrical conductivity, and lithium-ion diffusion coefficient during electrochemical processes. Furthermore, ultra-fine titanium powder, as the modifying agent, is amenable to large-scale production.  相似文献   

3.
Bi3.25La0.75Ti3-yNbyO12 (y=0.0, 0.03, 0.09, 0.15, 0.21) were synthesized using the solid-state reaction method. The effects of Nb doping on ferroelectric properties were studied through dielectric and P-E measurements. The value of Pr increases with increasing Nb content. Bi3.25La0.75Ti3-yNbyO12 ceramics exhibit a maximum remanent polarization of Pr=27 μC/cm2 at an Nb content of y=0.09. These results indicate that Nb doping can improve the ferroelectric properties of BLT ceramics. The Curie temperature, Tc, decreased with increasing Nb-content, and the ferroelectric phase transition of BLTNy is a second-order transition without thermal hysteresis. PACS 77.55.+f; 77.80.-e; 77.22.Jp  相似文献   

4.
Ferroelectric ceramics with formula Pb0.8Ba0.2[(In1/2Nb1/2)1-xTix]O3 (PBINT) (x=0.0,0.1,0.2,0.3,0.4 and 0.5) were prepared via a two-step solid state reaction method. It was found that ceramics with compositions in the range of x=0.0∼0.3 showed a pseudo-cubic structure, whereas the ceramic with x=0.5 displayed a tetragonal structure. All compositions showed significant frequency dispersion in their dielectric properties. The remanent polarization Pr as well as the coercive field Ec, measured at room temperature, increases with the Ti content. The experimental results obtained in this system are summarized into a phase diagram, with the morphotropic phase boundary (MPB) located at x=0.4. Compared with the Pb[(In1/2Nb1/2)1-xTix]O3 solid solution system, incorporating Ba in the A-site leads to a significant decrease in the dielectric maximum temperature Tmax, a suppression of the dielectric relaxation parameter γ, and a shift of the MPB composition to a higher Ti content. PACS 77.84.Dy; 77.80.Bh; 77.22.Ch  相似文献   

5.
Alumina micro- and nanopowders with the particle size from 200 μm to 40 nm synthesized by the sol-gel method are studied. The particle size dependence of γ-Al2O3→α-Al2O3 phase transformation is studied by differential thermal analysis, X-ray diffraction method, and transmission electron microscopy. X-ray diffraction data show that for alumina nanoparticles γ-Al2O3→θ-Al2O3 phase transformation occurs at 900°C, and for micro-particles it occurs in the temperature range 1150–1200°C. The alumina ceramics produced of alumina nanoparticles is shown to have higher flexural strength under three-point bending than the ceramics produced of micro-particles. The obtained results demonstrate that alumina particle size reduction stabilizes the formation of α-Al2O3 at lower temperatures, due to which the grain growth rate decreases and the flexural strength of monolithic oxide ceramics increases.  相似文献   

6.
Using an ordinary ceramic fabrication technique, we fabricated lead-free (1-x)(K0.5Na0.5)NbO3-xBa(Ti0.95Zr0.05)O3 ceramics with CuO sintering aid . Ba(Ti0.95Zr0.05)O3 diffuses into (K0.5Na0.5)NbO3 to form a new solid solution. The ceramics with perovskite structure possess orthorhombic phase at x≤0.04 and become tetragonal phase at x≥0.06. Both the paraelectric cubic–ferroelectric tetragonal and the ferroelectric tetragonal–ferroelectric orthorhombic phase transition temperatures decrease with increasing the concentration of Ba(Ti0.95Zr0.05)O3. The doping of CuO effectively promotes the densification of the ceramics. The coexistence of the orthorhombic and tetragonal phases at 0.04<x<0.06 and the improvement in sintering performances of the ceramics significantly enhance the piezoelectric and dielectric properties at room temperature. The ceramics with x=0.04–0.06 and y=0.75–1.50 possess excellent properties: d33=119–185 pC/N, kP=37–44%, kt=35–49%, ε=341–1129, cosδ=0.7–4.4% and Tc=312–346 °C. PACS 77.65.-j; 77.84.Dy; 77.84.-s  相似文献   

7.
The spinel structure of lithium titanate Li4Ti5O12 is refined by the Rietveld full-profile analysis with the use of x-ray and neutron powder diffraction data. The distribution and coordinates of atoms are determined. The Li4Ti5O12 compound is studied at high temperatures by differential scanning calorimetry and Raman spectroscopy. The electrical conductivity is measured in the high-temperature range. It is shown that the Li4Ti5O12 compound with a spinel structure undergoes two successive order-disorder phase transitions due to different distributions of lithium atoms and cation vacancies (□, V) in a defect structure of the NaCl type: (Li)8a[Li0.33Ti1.67]16dO4 → [Li□]16c[Li1.33Ti1.67]16dO4 → [Li1.330.67]16c[Ti1.670.33]16dO4. The low-temperature diffusion of lithium predominantly occurs either through the mechanism ... → Li(8a) → V(16c) → V(8a) → ... in the spinel phase or through the mechanism ... → Li(16c) → V(8a) → V(16c) → ... in an intermediate phase. In the high-temperature phase, the lithium cations also migrate over 48f vacancies: ... Li(16c) → V(8a, 48f) → V(16c) → ....  相似文献   

8.
Micro/nanoscopic Pb(Zr0.52Ti0.48)O3 fibers were synthesized from commercially available zirconium n-pro-poxide, titanium isopropoxide, and lead 2-ethylhexanoate. Using xylene as a solvent, they were mixed to form a precursor solution with a suitable viscosity for electrospinning. The solution was analyzed using thermo-gravimetric and differential thermal methods. Ultra-fine fibers and mats were electrostatically drawn from the precursor solution. The as-deposited materials were sintered for 2 h at 400, 500, 600, 700 and 800 °C, respectively. Sintered mats or fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Raman micro-spectrometry and scanning-probe microscopy (SPM). The SEM results revealed that the fibers had diameters varying from hundreds of nanometers to 10 m. Using AES, the elements Pb, Zr, Ti and O, as well as residual C, were detected on the surface of the fibers. Raman and XRD spectra indicated that the precursors began to transform into the intermediate pyrochlore phase at 400 °C, followed by the perovskite Pb(Zr0.52Ti0.48)O3 phase above 600 °C. Scanning-probe microscopy (SPM), operated in the piezo-response imaging mode, revealed spontaneous polarization domains in the fibers, with diameters ranging from 100 to 500 nm. PACS 61.46.+w; 77.90.+k; 81.07.-b; 81.16.-c  相似文献   

9.
Superconductivity was achieved in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The X-ray diffraction measurement shows that this material has a layered structure with the space group of P4/nmm, and with the lattice constants a = b = 3.9003 Å and c = 15.8376 Å. Clear diamagnetic signals in ac susceptibility data and zero-resistance in resistivity data were detected at about 6 K, confirming the occurrence of bulk superconductivity. Meanwhile we observed a superconducting transition in the resistive data with the onset transition temperature at 29.2 K, which may be induced by the nonuniform distribution of the Cr/Ti content in the FeAs-42622 phase.  相似文献   

10.
Nanocrystalline multiphase titanium oxycarbide (TiCxOy) thin films composed of TiC2, TiO0.325, Ti2O3 and graphitic carbon have been deposited on titanium substrates, using energetic carbon ions delivered by the UNU/ICTP and the NX2 plasma focus devices operated at different repetition rates. X-ray diffraction (XRD) patterns of the nanocomposite films reveal the relative transformation of various oxide and carbide phases accompanied by the suppression of the TiC2 phase when the energy flux of the ion beam and the repetition rate are increased. A field emission scanning electron microscope (FESEM) with an energy dispersive X-ray spectroscopy (EDS) attachment reveals a non-porous microcrack-free nanocrystalline granular surface morphology of the composite films with uniform carbon distribution. X-ray photoelectron spectroscopy (XPS) confirms the formation of oxycarbides (TiCxOy) along with significant carbon adsorbate. Raman studies of the films also verify the relative phase transformation in the TiCxOy nanocomposite by tuning the deposition parameters. The Vickers microhardness of the sample surface is improved more than 400%. PACS 52.59.Hq; 52.77.Dq; 68.55.Jk; 81.15.-z; 81.65.Lp  相似文献   

11.
PbZr0.53Ti0.47O3/LaNiO3 (PZT/LNO) hetero-structures have been successfully deposited on MgO, SrTiO3, Al2O3 and Si substrate by chemical solution routes, respectively. The X-ray diffraction measurements show that out-of-plane lattice parameters of PZT increase as increase of thermal expansion coefficient of substrate. Polarization fatigues of Pt/PZT/LNO capacitors are strongly affected by the thermal strain caused by difference of thermal expansion coefficient between PZT and substrate materials. High fatigue resistance of Pt/PZT/LNO can be obtained by using substrate with similar thermal expansion coefficient as PZT. PACS 77.84.Dy; 78.20.Ci; 81.20.Fw  相似文献   

12.
Al-Mo codoped Li7La3Zr2O12 ceramics with fine grain were prepared by sol-gel method. The influences of Al-Mo codoping on the structure, microstructure, and conductivity of Li7La3Zr2O12 were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and impedance spectroscopy. The cubic phase Li7La3Zr2O12 has been stabilized by partial substitution of Al for Li and Mo for Zr. Li6.6-3yAlyLa3Zr1.8Mo0.2O12 (0?≤?y?≤?0.1) has been sintered at 1040–1060 °C for 3 h. The liquid sintering facilitated its densification. The relative density of the composition with x?=?0.075 was approximately 96.4%. Results indicated that the Al-Mo codoped LLZO synthesized by sol-gel method effectively lowered its sintering temperature, accelerated densification, and improved the ionic conductivity.  相似文献   

13.
(K0.5Na0.5)(Nb1-xTax)O3 lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique. The results of X-ray diffraction reveal that Ta5+ diffuses into the K0.5Na0.5NbO3 lattices to form a solid solution with an orthorhombic perovskite structure. Because of the high melting temperature of KTaO3, the (K0.5Na0.5)(Nb1-xTax)O3 ceramics can be sintered at higher temperatures. The partial substitution of Ta5+ for the B-site ion Nb5+ decreases both paraelectric/cubic–ferroelectric/tetragonal and ferroelectric/tetragonal–ferroelectric/orthorhombic phase transition temperatures, TC and TO-T. It also induces a relaxor phase transition and weakens the ferroelectricity of the ceramics. The ceramics become ‘softened’, leading to improvements in d33, kp, kt and εr and a decease in Ec, Qm and Np. The ceramics with x=0.075–0.15 become optimum, having d33=127–151 pC/N, kp=0.43–0.44, kt=0.43–0.44, εr=541–712, tanδ=1.75–2.48% and TC=378–329 °C. PACS 77.65.-j; 77.84.Dy; 77.84.-s  相似文献   

14.
Li4Ti5O12/Cu2O composite was prepared by ball milling Li4Ti5O12 and Cu2O with further heat treatment. The structure and electrochemical performance of the composite were investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Li4Ti5O12/Cu2O composite exhibited much better rate capability and capacity performance than pristine Li4Ti5O12. The discharge capacity of the composite at 2 C rate reached up to 122.4 mAh g?1 after 300 cycles with capacity retention of 91.3 %, which was significantly higher than that of the pristine Li4Ti5O12 (89.6 mAh g?1). The improvement can be ascribed to the Cu2O modification. In addition, Cu2O modification plays an important role in reducing the total resistance of the cell, which has been demonstrated by the electrochemical impedance spectroscopy analysis.  相似文献   

15.
The relaxor ceramics PbSc0.5Ta0.5O3 produced from an ultradispersed powder is studied by X-ray diffraction and dielectric measurements. Before sintering, the powder was subjected to treatment in Bridgman anvils in combination with shear deformation. This method is shown to affect the order parameter and dielectric properties of the ceramics without using long-term high-temperature annealing.  相似文献   

16.
A Li0.5FeV1.5O4 sample was synthesized using sol-gel route. The X-ray diffraction study indicates formation of spinel phase (with Fd3m space group) for this sample. LiO4, LiO6, and V-O bonds were identified from the Raman spectrum, while LiO4 and Fe-O bonds were identified from the FTIR spectrum of this sample phase. The FESEM study indicates formation of inhomogeneous grains. The surface area of 74.39 m2/g was estimated from the Brunauer-Emmett-Teller (BET) surface area analysis technique. The cyclic voltammetry study of Li0.5FeV1.5O4 indicates an anodic peak at 2.1 V while a cathodic peak at 1.98 V. The charge-discharge study exhibits two voltage plateaus respectively at 2.1 and at 4 V. Stable electrochemical capacity of 40 mAh/g for Li0.5FeV1.5O4 was found for 30 cycles. The electrochemical impedance spectroscopy study indicates smaller bulk resistance and higher ionic diffusion, i.e., less Warburg impedance for this phase. An energy density of 89 Wh/kg, a power density of 33 W/kg, and a 90% Coulombic efficiency was achieved with relatively good cyclic stability from Li0.5FeV1.5O4.  相似文献   

17.
Carbon encapsulated Li4Ti5O12 (C/Li4Ti5O12) anode material for lithium ion battery was prepared by using the pre-coat method of two steps, and the TiO2 was pre coated before the reaction with Li2CO3. The structure and morphology of the resultant C/Li4Ti5O12 materials were characterized by X-ray diffraction (XRD) and scanning microscopy (SEM). Electrochemical tests showed that at 0.1 C, the initial discharge capacity was 169.9 mAh g?1, and the discharge capacity was 80 mAh g?1 at 5 C. After 100 cycles at 2 C, the discharge specific capacity was 108.5 mAh g?1. Compare with one step coating method, results showed the C/Li4Ti5O12 prepared by pre-coat method can reduce the particle’s size and effectively improve the electrochemical performance.  相似文献   

18.
Polycrystalline samples of SrFe2/3W1/3O3 (SFWO) ceramic were obtained by solid-phase reactions with subsequent sintering using conventional ceramic technology. X-ray diffraction analysis showed that at room temperature, the SFWO ceramic is single-phase and has a perovskite-type structure with tetragonal symmetry and parameters a = 3.941(9) Å, c = 3.955(6) Å, and c/a = 1.0035. In studying the magnetic properties and the Mössbauer effect in SFWO ceramics, it is found that the material is a ferrimagnet, and the iron ions are only in the valence state of Fe3+. It is suggested that in the temperature range of T = 150–210°C, a smeared phase transition from a cubic (paraelectric) phase to a tetragonal (ferroelectric) phase takes place in SFWO with decreasing temperature.  相似文献   

19.
New perovskite solid solution ceramics of (1−x)BaTiO3-xBi(Mg1/2Ti1/2)O3 ((1−x)BT-xBMT, x≤0.09) were synthesized by the solid-state reaction technique. X-ray diffraction studies have revealed a stable single perovskite structure for all samples. Dielectric measurements were carried out at different frequencies and temperatures. The polarization evolutions with temperatures were measured to investigate the ferroelectric properties. All the compositions show features of ferroelectrics with diffuse phase transition, though the temperature T m of their dielectric constant maximum ε m is frequency dependent. The dielectric constant peak ε(T) of (1−x)BT-xBMT ceramics become broad with increasing BMT content. During the temperature range of ε(T) peak summit, (1−x)BT-xBMT ceramics present quasi-linear dielectric phenomenon under high electric field with very high dielectric constant.  相似文献   

20.
The Ba0.4Sr0.6−x Mn x TiO3 (BSMT) ceramics with different Mn composition (from 1% to 10%) have been prepared via the conventional solid-state reaction sintering. The X-ray diffraction analysis shows that the ceramics are polycrystalline with the single perovskite phase. The lattice vibrations and optical properties have been investigated using Raman scattering, spectroscopic ellipsometry (SE), and infrared reflectance spectra. It was found that the optical bandgap for the BSMT ceramics is varied between 3.40 and 3.65 eV. The three first-order Raman-active phonon modes can be observed, and the frequency of the A 1(LO3)/E(LO) mode shows a blue shift of 8 cm−1 with the Mn composition, which can be attributed to the distortion of the TiO6 octahedron. With increasing Mn composition, the frequency of the infrared-active TO4 mode decreases from 532 to 520 cm−1, owing to the local variation of the lattice constant induced by the Mn incorporation. Moreover, the optical functions of the ceramics from the far-infrared to ultraviolet region are obtained based on the SE and reflectance spectra, which is useful for the potential applications in ferroelectric-based optoelectronic devices.  相似文献   

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