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1.
J.-H. Park J.-S. Bae B.-E. Jun B.-C. Choi J.-H. Jeong 《Applied Physics A: Materials Science & Processing》2007,86(1):63-65
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
2.
A. Akrap R. Gaal L. Forró 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):287-291
We investigate the pressure and temperature behavior of current-dependent resistivity of β-SrV6O15. We observe a switching between states of different resistivities in the insulating state of β-SrV6O15. In the low pressure phase, the resistive switching appears at temperatures below the semiconductor-insulator transition.
In the high pressure phase, under ~1.6 GPa, the switching appears in the temperature range of the phase transition. The existence
of switching may imply an important role of strontium off-stoichiometry for the electrical transport in β-SrV6O15. No electric-field-induced enhancement of the conductivity is observed. However, the conduction is significantly nonlinear
under ~1.6 GPa, indicating that the charge order pattern in the high pressure phase is considerably different from that of
the low pressure phase. 相似文献
3.
AC impedance spectroscopy technique has been used to study electrical properties of Bi3.25La0.75Ti3O12 (BLT) ceramic. Complex impedance plots were fitted with three depressed semicircles, which are attributed to crystalline
layer, plate boundary and grain boundary and all three were found to comprise of universal capacitance nature [C = C0w
n−1]. Grain boundary resistance and capacitance evaluated from complex impedance plots have larger values than that of plate
boundary and crystalline layer. The activation energies (E
a) for DC-conductance in grain boundary, plate boundary and crystalline layer are 0.68 eV, 0.89 eV and 0.89 eV, respectively.
Relaxation activation energies calculated from impedance plots showed similar values, 0.81 eV and 0.80 eV for crystalline
layer and plate boundary, respectively. These activation energy values are found to be consistent with the E
a value of oxygen vacancies in perovskite materials. A mechanism is offered to explain the generation of oxygen vacancies in
BLT ceramic and its role in temperature dependence of DC-conductance study.
相似文献
4.
Banarji Behera Pratibindhya Nayak Ram N. P. Choudhary 《Central European Journal of Physics》2008,6(2):289-295
A polycrystalline sample of KCa2Nb5O15 with tungsten bronze structure was prepared by a mixed oxide method at high temperature. A preliminary structural analysis
of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound shows a uniform
grain distribution throughout the surface of the sample. Studies of temperature variation on dielectric response at various
frequencies show that the compound has a transition temperature well above the room temperature (i.e., 105°C), which was confirmed
by the polarization measurement. Electrical properties of the material have been studied using a complex impedance spectroscopy
(CIS) technique in a wide temperature (31–500°C) and frequency (102–106 Hz) range that showed only bulk contribution and non-Debye type relaxation processes in the material. The activation energy
of the compound (calculated from both the loss and modulus spectrum) is same, and hence the relaxation process may be attributed
to the same type of charge carriers. A possible ‘hopping’ mechanism for electrical transport processes in the system is evident
from the modulus analysis. A plot of dc conductivity (bulk) with temperature variation demonstrates that the compound exhibits
Arrhenius type of electrical conductivity.
相似文献
5.
Highly c-axis-oriented Sr3Bi4Ti6O21 (SBTi) thin films were fabricated on Pt-coated Si substrates by pulsed laser deposition (PLD). The structures were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). No peaks of SrTiO3 (STO) could be detected in the XRD pattern, indicating the existence of the SBTi single phase. Good ferroelectric hysteresis loops of the films with Pt electrodes were obtained. With an applied field of 400 kV/cm, the measured remanent polarization (Pr) and coercive field (Ec) values were 4.1 C/cm2 and 75 kV/cm respectively. The films showed little fatigue after 2.22×109 switching cycles: the nonvolatile polarizations decreased by less than 5% of the initial values. The dielectric constant and the loss tangent of the films were measured to be 363 and 0.04 at 100 kHz. These results might be advantageous for nonvolatile ferroelectric random access memory (NVFRAM) and dynamic random access memory (DRAM). PACS 77.84.Dy; 77.22.-d; 68.55.Jk 相似文献
6.
Glass-forming ability (GFA) and thermal stability of Fe62Nb8B30, Fe62Nb6Zr2B30 and Fe72Zr8B20 at % amorphous alloys were investigated by calorimetric (DSC and DTA) measurements. The crystallization kinetics was studied
by DSC in the mode of continuous versus linear heating and it was found that both the glass transition temperature, T
g
, and the crystallization peak temperature, T
p
, display strong dependence on the heating rate. The partial replacement of Nb by Zr leads to lower T
g
and T
x
temperatures and causes a decrease of the supercooled liquid region. JMA analysis of isothermal transformation data measured
between T
g
and T
x
suggests that the crystallization of the Fe62Nb8B30 and Fe62Nb6Zr2B30 amorphous alloys take place by three-dimensional growth with constant nucleation rate. Nb enhances the precipitation of the
metastable Fe23B6 phase and stabilizes it up to the third crystallization stage. Zr addition increases the lattice constant of Fe23B6 and, at the same time, decreases the grain size. 相似文献
7.
Priyadarshini S. Sahoo Anuradha Panigrahi Sunanda K. Patri Ram N. P. Choudhary 《Central European Journal of Physics》2008,6(4):843-848
Polycrystalline samples of Ba4SrRTi3V7O30 (R=Sm and Dy), members of the tungsten-bronze family, were prepared using a high-temperature, solid-state reaction technique
and studied their electrical properties (using complex impedance spectroscopy) in a wide range of temperature (31–500°C) and
frequency (1 kHz-1 MHz). Preliminary structural (XRD) analyses of these compounds show the formation of single-phase, orthorhombic
structures at room temperature. The scanning electron micrographs (SEM) provided information on the quality of the samples
and uniform distribution of grains over the entire surface of the samples. Detailed studies of the dielectric properties suggest
that they have undergone ferroelectric-paraelectric phase transition well above the room temperatures (i.e., 432 and 355°C
for R= Sm and Dy, respectively, at frequency 100 kHz). Measurements of electrical conductivity (ac and dc) as a function of
temperature suggest that the compounds have semiconducting properties much above the room temperature, with negative temperature
coefficient of resistance (NTCR) behavior. The existence of ferroelectricity in these compounds was confirmed from a polarization
study.
相似文献
8.
J. Rymarczyk D. Machura J. Ilczuk 《The European physical journal. Special topics》2008,154(1):187-190
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
9.
S. K. Jain A. Das Bipin K. Srivastava Anjali Krishnamurthy S. K. Paranjpe 《Pramana》2004,63(2):207-212
Magnetization and neutron diffraction measurements have been made on the title pseudo-binary of tetragonal anti-ferromagnets
Fe2 As and Cr2 As. In this system antiferromagnetic (AFM) ordering appears below 310 K. The moments are confined in theab plane but unlike in the end members they are tilted off thea-axis. In addition to the AFM structure a weak ferromagnetic behaviour shows up below∼80 K with a rather low moment of ∼0.07
μB per formula unit at 5 K and under a field of 3 T. 相似文献
10.
D. Do S. S. Kim S. W. Yi J. W. Kim 《Applied Physics A: Materials Science & Processing》2009,94(3):697-701
Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi4Ti4O15 grown on Bi4Ti3O12, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared
on a Pt(111)/Ti/SiO2/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin
films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P
r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm2 at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 1010 switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi4Ti4O15 on Bi4Ti3O12 ferroelectric thin films were better than those of the SrBi4Ti4O15 grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth
kinetics of SrBi4Ti4O15 on the c-axis-oriented Bi4Ti3O12 layer or on the Pt-coated Si substrate. 相似文献
11.
Jungang Hou R. V. Kumar Yuanfang Qu Dalibor Krsmanovic 《Journal of nanoparticle research》2010,12(2):563-571
Bi4Ti3O12 (BIT) nanoparticles with a narrow average particle size distribution in the range of 11–46 nm was synthesized via a metal-organic polymeric precursor process. The crystallite size and lattice parameter of BIT were determined by XRD analysis. At annealing temperatures >550 °C, the orthorhombic BIT compound with lattice parameters a = 5.4489 Å, b = 5.4147 Å, and c = 32.8362 Å was formed while at lower annealing temperatures orthorhombicity was absent. Reaction proceeded via the formation of an intermediate phase at 500 °C with a stoichiometry close to Bi2Ti2O7. The particle size and the agglomerates of the primary particles have been confirmed by FESEM and TEM. The decomposition of the polymeric gel was ascertained in order to evaluate the crystallization process from TG-DSC analysis. Raman spectroscopy was used to investigate the lattice dynamics in BIT nanoparticles. In addition, investigation of the dependence of the visible emission band around the blue–green color emission on annealing temperatures and grain sizes showed that the effect of grain size plays important roles, and that oxygen vacancies may act as the radiative centers responsible for the observed visible emission band. 相似文献
12.
Microstructures and impedance characteristics of chemical-solution-derived Bi3.15Nd0.85Ti3O12 thin films were studied as functions of temperature. A dielectric anomaly was found at around 450°C, corresponding to the
paraelectric to ferroelectric transition. Via complex impedance studies, grain and grain boundary contributions to the impedance
were separated. The resistance of grain and grain boundaries is found governed by the same kind of space charge with an activation
energy around 1.1 eV, close to that of oxygen vacancies in perovskite ferroelectrics. The low temperature ac conductance of
BNdT thin films shows a frequency dispersion, which can also be ascribed to space charges mainly due to oxygen vacancies.
The results were compared with SrBi2Ta2O9 in terms of oxygen vacancy conductivity. 相似文献
13.
Nonstoichiometric Bi2WO6 photocatalyst with the composition of Bi2?+?x WO6?+?1.5x (?0.25 ≤ x ≤ 1) wa synthesized by a facile solid state reaction method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The Bi2.5WO6.75 photocatalyst showed excellent visible-light-driven photocatalytic performance; nearly 100 % of RhB (10 ppm, pH?=?3?~?4) was decomposed within 25 min, which demonstrated that nonstoichiometric semiconductors could be an efficient visible-light-driven photocatalyst. 相似文献
14.
E. García-Matres N. Stüßer M. Hofmann M. Reehuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):35-42
The magnetic structures of Mn1-xFexWO4 with x
= 0.0, 0.16, 0.21, 0.225, 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase
diagram could be completed in the coexistence range of different magnetic structures up to x
= 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector
= (±1/4, 1/2, 1/2) was found for x
⩽ 0.22 while the magnetic spins order with
= (1/2, 0, 0) for x
≥ 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with
= (- 0.214, 1/2, 0.457) occur in the diffraction pattern up to x
= 0.29 indicating the occurence of a reentrant phase. For 0.12 ⩽
x
⩽ 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed
to a spin arrangement with
= (1/2, 0, 0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed
Mn2+- and Fe2+-ions in the coexistence range 0.12 ⩽
x
⩽ 0.29 of different magnetic structures related to those of pure MnWO4 and FeWO4.
Received 9 October 2002 Published online 14 March 2003 相似文献
15.
Jungang Hou Yuanfang Qu Dalibor Krsmanovic R. V. Kumar 《Journal of nanoparticle research》2010,12(5):1797-1805
Well-dispersed bismuth titanate (BIT) nanocrystals with an average size ranged from 3 to 60 nm were synthesized via a peroxide-based
route assisted with an inverse microemulsion process. The crystallite size and lattice parameter of BIT upon variable-temperature
were determined by X-ray diffraction (XRD). The particle size was confirmed by transmission electron microscopy (TEM). Thermal
decomposition behaviour of Ti-peroxy and BIT gel and crystallization kinetics of BIT nanocrystals were investigated by differential
scanning calorimetry/thermogravimetry (DSC/TG) and Fourier-Transform infrared spectroscopy (FTIR). Analysis of nonisothermal
DSC data yielded a value of 220.84 ± 2.73 KJ/mol and 2.25 ± 0.26 for the activation energy of crystallization (E
a) and the Avrami exponent (n), respectively. 相似文献
16.
The thermodynamics structural relaxation of Fe73Cu1.5Nd3Si13.5B9 amorphous alloy from room temperature to 400°C has been investigated by measuring the structure factor with in situ X-ray diffraction. The structural information of the atomic configuration such as radial distribution function (RDF) and
neighbor atomic distance was gained by Fourier transformation. The research result shows that the amorphous structure remains
stable in the temperature range of 30 to 400°C but exhibits distinct changes in local atomic configuration with the increase
of temperature. The quantitative determination of the neighbor atomic distance suggests that the degree of short-range order
changes by the temperature altering the second nearest neighbor local atomic configuration of the amorphous when structural
relaxation occurs.
Supported by the Natural Science Foundation of Hebei Province of China (Grant No. A2007000296), the National Natural Science
Foundation of China (Grant No. 50731005), SKPBRC (Grant Nos. 2007CB616915 and 2006CB605201), and PCSIRT (Grant No. IRT0650) 相似文献
17.
H. He W. Y. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):457-463
The spin-states of cobalt based perovskite compounds depend sensitively
on the valence state and local crystal environment of Co ions and the
rich physical properties arise from strong coupling among charge, spin,
and orbital degrees of freedom. While extensive studies have been carried
out in the past, most of them concentrated on the isotropic compound
LaCoO3. In this paper, using the unrestricted Hartree-Fock approximation
and the real-space recursion method, we have investigated the competition
of various magnetically ordered spin-states of anisotropic double-layered
perovskite Sr2Y0.5Ca0.5Co2O7. The energy
comparison among these states shows that the nearest-neighbor
high-spin-intermediate-spin ferromagnetically ordered state is the relevant
magnetic ground state of the compound. The magnetic structure and sizes of
magnetic moments are consistent with the recent experimental observation. 相似文献
18.
Bi3.25Pr0.75Ti3O12 (BPT) ferroelectric thin films have been prepared by chemical solution deposition on platinized Si substrates. Well-crystallized BPT films can be achieved by 600 °C rapid thermal annealing. The film surface is smooth and crack-free, composed of uniform spherical grains around 90–100 nm in diameter. The electrical properties of Pt/BPT/Pt thin film capacitors were characterized by hysteresis and impedance measurements. The remanent polarization of 700 °C annealed BPT films is around 20 C/cm2 at 120-kV/cm stimulus field. The dielectric constant is around 380 at 10 kHz, 100-mV amplitude. The remanent polarization of BPT film showed a slight reduction, 10% of its original value, after 2.8×109 cycles, while a 30% reduction of non-volatile polarization was observed. PACS 81.15.-z; 77.55.+f; 77.22.Gm 相似文献
19.
Nearly all displacive transitions have been considered to be continuous or second order,and the rigid unit mode(RUM) provides a natural candidate for the soft mode.However,in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in BaWO 4:a 1.6% volume collapse,coexistence of phases,and hysteresis on release of pressure.Such first-order signatures are found to be the same as the soft modes in BaWO 4,which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism.By the refinement of atomic displacement parameters,we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaO 8 polyhedrons to the small displacive distortion of rigid WO 4 tetrahedrons.Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds. 相似文献
20.
Zhaoxia Bi Rong Zhang Weiping Li Xusheng Wang Shulin Gu Bo Shen Yi Shi Zhiguo Liu Youdou Zheng 《中国科学G辑(英文版)》2003,46(1):41-46
With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al2O3 substrate, ZnAl2O4/α-Al2O3 complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl2O4 changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding
scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl2O4 transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present
that ZnAl2O4 prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl2O4/α-Al2O3 substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD).
XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl2O4 layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results
indicate that islands on thin ZnAl2O4 layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film. 相似文献