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C.J. Xiao W.W. Zhang S.M. Feng X.H. Wang L.T. Li 《Journal of Physics and Chemistry of Solids》2007,68(2):311-314
Dense nanocrystalline BaTiO3 ceramics with uniform grain sizes of 30 nm was obtained by pressure assisted sintering. The phase transitions were investigated by Raman scattering at temperatures ranging from −190 to 200 °C. With increasing temperature, similar to 3 μm BaTiO3 normal ceramics, the successive phase transitions from rhombohedral to orthorhombic, orthorhombic to tetragonal, tetragonal to cubic were also observed in 30 nm BaTiO3 ceramics. Especially, the coexistence of ferroelectric tetragonal and orthorhombic phases was found at room temperature. The ferroelectric behavior was further characterized by P-E hysteresis loop. The experimental results indicate that the critical grain size of the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. 相似文献
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Ferroelectric behaviour of 30nm BaTiO3 ceramics prepared by high pressure assisted sintering 下载免费PDF全文
Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the 'dilution' effect of grain boundaries. 相似文献
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Lead-free piezoelectric ceramics (1 - x) (Na0.53K0.404 Li0.066)Nb0.92 Sb0.08 03 +xZrTiO3 are fabricated by conventional solid-state sintering method, and their dielectric and piezoelectric characteristics are investigated. With the addition of SrTiO3, the growth of the grain size is restrained, meanwhile the phase transition temperature of orthorhombic-tetragonal is shifted below room temperature. It is found that the ceramics with x = 0.010 exhibit excellent piezoelectric properties (d33 = 220 pC/N, kp = 41%, kt = 39%) and improved thermal stability around room temperature. The results indicate that these materials are promising lead-free piezoceramics for practical operations. 相似文献
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La0.8Sr0.2AlO3 (LSAO) thin films are grown on SrTiO3 (STO) and MgO substrates by laser molecular beam epitaxy. The LSAO thin film on oxygen deficient STO substrate exhibits metallic behaviour over the temperature range of 80--340K. The optical transmittance spectrum indicates that theLSAO thin films on MgO substrate are insulating at room temperature. The transport properties of LSAO thin films on STO substrates deposited in different oxygen pressure are compared. Our results indicate that oxygen vacancies in STO substrates should be mainly responsible for the transport behaviour of LSAO thin films. 相似文献
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Due to the fault of the first author, this article entitled “The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO3 thin films”, published in “Chinese Physics B”, 2011,Vol.20, Issue 12, Article No. 127701, has been found to copy from the article entitled“Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO3 thin films”, published in “Journal of Applied Physics”, 2011,Vol.109, Issue 8, article No. 084105.
So the above article in “Chinese Physics B” has been withdrawn from the publication.< 相似文献
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Ferroelectric Properties of Polycrystalline Ceramics with Dipolar Defect Simulated from the Potts--Ising Model 下载免费PDF全文
Physical properties of polycrystailine ferroelectrics including the contributions of the fixed dipolar defects and the average grain size in the Potts-Ising model are simulated by using the Monte Carlo method. Domain pattern, hysteresis loop and switching current of the polarization reversal process are obtained. Two processes are considered in our simulation. In the first one, the grain texture of ferroelectric ceramics are produced from the Ports model, and then the Ising model is implemented in the obtained polycrystailine texture to produce the domain pattern, hysteresis loop and switching current. It is concluded that the defect has the ability to decrease the remnant polarization P~ as well as the coercive field E~. The back switching is obviously observed after the electric field is off, and it shows some variation after introducing the fixed dipolar defect. Meanwhile, the spike of the switching current is found to lower with the increasing defect concentration and the decreasing average grain size. 相似文献
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Donor doped positive temperature coefficient of resistivity barium titanate is highly sensitive to minor changes in processing conditions, Ba/Ti ratio, and dopant concentration. This leads to a lack of reproducibility of properties and microstructure. This study was performed in an effort to obtain a more microstructurally stable PTCR material. Barium titanate ceramics were prepared by blending Ba-excess BaTiO3 powder with Ti-excess powder, in different ratios. Such donor modified blended systems display uniform, medium grain size (4-6 μm), high-density microstructures which are more stable to changes in processing parameters. The microstructures are characterized by flat grain edges, large grain-to-grain contact area and high degree of domain coherence across grain boundaries. The PTCR effect was, however, measured to be nominal in these samples. This has been attributed to the presence of a smaller barrier potential, and such microstructural features as strong domain coherence across grain boundaries, large grain-to-grain contact area, and high density. It was found that the simple act of blending donor doped BaTiO3 powders of different Ba/Ti ratios drastically changes both microstructure and electrical properties. Blending results in the suppression of liquid-phase induced anomalous grain growth, suppressing grain growth processes and allowing sintering processes to go to a greater degree of completion. The proposed mechanism whereby this happens is that the presence of the donor in blended systems either changes the kinetics of liquid-phase formation and/or the wettability of grains, affecting liquid-phase distribution. 相似文献
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Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Crystallized inDifferent N2/O2 Ambients 下载免费PDF全文
Bi3.25La0.75 Ti3O12 (BLT) ferroelectric thin films are deposited by sol-gel method and annealed for crystallizaion in total l eccm N2/02 mixed gas with various ratio at 750℃ for 30rain. The effect of crystallization ambient on the structural and ferroelectric properties of the BLT films is studied. The growth direction and grain size of BLT film are revealed to affect ferroeleetric properties. Alter the BLT film is annealed in 20%O2, the largest P~ value is obtained, which is ascribed to an increase of random orientation and large grain size. The fatigue property is improved with the concentration of oxygen in the ambient increasing, which is ascribed to annealing in the ambient with high concentrated oxygen adequately decreasing the defects related to lack of oxygen. 相似文献
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A. Kumar M.R. Alam J.J. Weimer L. Sanderson 《Applied Physics A: Materials Science & Processing》1999,69(7):S917-S920
TiNi thin films with BaTiO3 and PbZr0.52Ti0.48O3 (PZT) as buffer layers were deposited on Si(100) substrates by the pulsed laser deposition (PLD) method. Buffer layers (BaTiO3 and PZT) were deposited at 600 °C in oxygen (O2) environment and TiNi films were deposited on the top of the buffer layer in presence of 15 mTorr nitrogen (N2) at various deposition temperatures (50, 300, and 500 °C). Synthesis and characterization of TiNi films were investigated from the crystallographic point of view by using X-ray diffractometer (XRD) and atomic force microscope (AFM) techniques. It is found that buffer layer of BaTiO3 and PZT have improved the crystallinity of TiNi films deposited at higher temperatures. The TiNi/PZT film was uniform compared to TiNi/BaTiO3 film with the exception of agglomerates that appeared throughout the layer. 相似文献
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系统地研究了在0~3 MPa氧压下T1系超导材料的制备过程及其超导性质。结果表明:0.25~0.90 MPa氧压下所制备的样品为纯2223相,Tc0最高可达125.3 K;1.45~3.00 MPa氧压下样品为纯2212相,Tc0在95~100 K之间;0.90~1.45 MPa氧压下样品为2223及2212两相共存。对两种单相样品的高压研究结果表明,2223相样品比2212相样品有着较强的压力效应,在0~0.52 GPa压力下分别为4.0 K/GPa及2.0 K/GPa。 相似文献
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This paper reports that polycrystalline α-Al2O3:C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence (TL) and optical stimulated luminescence (OSL) of α-Al2O3:C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F+ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610K. The attenuation constant of exponentially decaying fast component (τ1) and slow component(τ2) of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al2O3:C crystal. 相似文献
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Upconversion Luminescence of Er3+ Ions in Transparent Germanate Glass Ceramics Containing CaF2 Nanocrystals 下载免费PDF全文
The visible upconversion and near-infrared luminescence of Er3+ ions in germanate glass ceramics containing GaF2 nanocrystals are investigated. The nanocrystals are characterized by x-ray diffraction (XRD) and transmission electron microscopy, showing their mean sizes less than 20hm. High transmittance of the glass ceramics is displayed by absorption spectra. The upconversion luminescence intensity in the glass ceramics increases significantly with increasing temperature. Both the shifts of the XRD peaks and the Stark-split shown in the luminescence spectra indicate the entrance of the Er3+ ions into the CaF2 nanocrystals, which is confirmed by a Judd-Ofelt analysis. Possible mechanisms of the upconversion luminescence are analyzed. 相似文献
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Z. Valdez-Nava S. Guillemet-Fritsch T. Lebey B. Durand 《Journal of Physics and Chemistry of Solids》2011,72(1):17-23
BaTiO3−x and Ba0.95La0.05TiO3−x nanoceramics showing colossal permittivity values have been characterized. While starting powders are of cubic symmetry, X-ray and Neutron Diffraction techniques and Raman Spectroscopy measurements show that the one-step processed ceramics obtained by Spark Plasma Sintering (SPS) contain cubic and tetragonal phases. Rather large oxygen deficiency determined in such ceramics by Electron Micro Probe analysis and Electron Energy Loss Spectroscopy analyzes is explained by the presence of Ti3+, as evidenced by X-ray Photoelectron Spectroscopy measurements. Transmission Electron Microscopy and High Resolution Transmission Electron Microscopy show that these ceramics contain 50-300 nm grains, which have single-domains, while grain boundaries are of nanometer scale. Colossal permittivity values measured in our dense nanoceramics are explained by a charge hopping mechanism and an interfacial polarization of a large number of polarons generated after sample reduction in SPS apparatus. 相似文献
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Jian Quan Qi Li Sun Wan Ping Chen You Guo Xu Ce Wen Nan 《Journal of Physics and Chemistry of Solids》2010,71(12):1676-1679
The formation mechanism of excess titanium in BaTiO3 nanoparticles is different from that in BaTiO3 bulk materials. In this study, we analyzed the concentration of excess titanium in BaTiO3 nanoparticles, which were directly synthesized from solution at 65 °C and it was found that it can reach an abnormal high concentration and keep the normal perovskite structure. The mechanism is discussed from the points of both defect chemistry and surface effect. The dielectric property of the ceramics fabricated from as-prepared nanoparticles with different concentration of excess titanium is also studied. 相似文献
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InP film samples were prepared by spray pyrolysis technique using aqueous solutions of InCl3 and Na2HPO4, which were atomized with compressed air as carrier gas onto glass substrates at 500°C with different thicknesses of the films. It is found that the resistivity of the polycrystalline films strongly depends on the grain size. It is observed that the grain size of the films increase with the decrease of the energy band gap and strain of the film. The changes observed in the energy band gap and strain related to the film grain size of the films are discussed in detail. 相似文献
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Phase Transition and Melting Curves of Calcium Fluoride via Molecular Dynamics Simulations 下载免费PDF全文
The phase transition and melting curves of CaF2 are investigated by using the general utility lattice programme (CULP) via the shell model with molecular dynamics method. By calculating the entropy H (at OK) and Cibbs free energy G^* (at 30OK), we find that the phase transition pressure from the face-centred cubic (fee) structure to the orthorhombic structure is 11.40 CPa and 9.33 CPa at OK and 300K, respectively. The modified melting point of the fee CaF2 is in the range of 1650-1733K at OCPa. All these results are well consistent with the available experimental data and other theoretical results. We also obtain that the melting temperature of high pressure phase is 990-1073 K at 10 CPa. Moreover, the temperature dependences of the elastic constants Cij, bulk module B and shear module G are also predicted. 相似文献
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S. Tirumala S.B. Desu A. Rastogi 《Applied Physics A: Materials Science & Processing》2000,70(3):253-259
Crystallization of SrBi2Ta2O9 (SBT) thin films was studied as a function of viscosity of bismuth precursor and baking temperature, in order to fabricate capacitors with improved ferroelectric properties. SBT thin films were deposited on to Pt substrates using a chemical solution deposition (CSD) technique. Post-deposition anneal at 750 °C for 1 h in oxygen atmosphere revealed a significant influence of baking temperature and the viscosity of bismuth precursor on the microstructure and the ferroelectric properties of SBT thin films. A high baking temperature (350 °C) and a low viscosity of bismuth precursor (8 cp) yielded larger amounts of Bi2O3 secondary phase, smaller SBT grains (104 nm), and lower remanent polarization (Pr=2.0 7c/cm2). Additionally, these films exhibited a very high rate of ageing (>45% reduction in Pr after 7 days). A modified CSD process is suggested, which could suppress the formation of Bi2O3 secondary phase. Films fabricated using modified CSD technique exhibited a much larger grain size of 165 nm, higher Pr of 7.2 7c/cm2, and significantly improved ageing characteristics (<1% reduction in Pr after 7 days). A qualitative model to describe the ageing in SBT-based capacitors is also suggested. 相似文献
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In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/Vo - P relationship (V and Vo are the volumes at pressure P and at atmosphere). The bulk modulus Bo is calculated based on the Birch-Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160K. 相似文献