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171.
《Current Applied Physics》2014,14(5):757-760
CaTiO3 is a well-known incipient ferroelectric material that does not undergo a ferroelectric phase transition in spite of the intriguing dielectric constant behavior. Especially, unlike a prototypical incipient ferroelectric SrTiO3, the paraelectric state of CaTiO3 cannot be easily destroyed by small perturbations, including cation doping and epitaxial strain. We present that a nearly strain-free epitaxial CaTiO3 film grown at a low oxygen partial pressure exhibits polarization–voltage hysteresis loops and the distinct difference of piezoresponse force microscopy phase signals, implying that a ferroelectric phase is induced. Such results are shown even at room temperature. We suggest that the observed ferroelectric behavior in CaTiO3 film comes from the defect dipoles composed of vacancies inside the film. Using electron-probe microanalysis and optical absorption spectra measurements, we found that CaTiO3 film has considerable Ca and O vacancies, forming the localized defect state in electronic structure. This work highlights the importance of vacancies and their clusters, such as defect dipoles, in understanding the electronic properties of perovskite oxide thin films, including ferroelectricity. 相似文献
172.
Asymmetric reversible diode-like resistive switching behaviors in ferroelectric BaTiO3 thin films 下载免费PDF全文
In this work, the resistive switching behaviors of ferroelectrictric BaTiO3/La0.67Sr0.33MnO3 .heterostructures de- posited by pulsed laser deposition are investigated. The BaTiO3 films show both well-established P-E hysteresis loops, and asymmetric reversible diode-like resistive switching behaviors, involving no forming process. It is found that both the ON/OFF ratio and the stability of resistive switching are substantially dependent on operation voltage (Vmax). At a Vmax of 15 V, a large ON/OFF resistance ratio above 1000 is obtained at a Vmax of 15 V, which is able to maintain stability up to 70-switching cycles. The above resistive switching behaviors can be understood by modulating interface Schottky barriers as demonstrated by I-V curve fitting. 相似文献
173.
Tuning the dielectric permittivity spectra of strontium titanate (SrTiO3) single crystals in an extemal optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. The application of the optical field leads to an appreciable tuning of the permittivity, reaching up to 2.8%, with the dielectric loss changing about 3%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of the refractive index responds linearly to the applied light power. These findings are attributed to a linear electro-optical effect of the internal space charge field of the crystal. 相似文献
174.
Shunsuke Kobinata Yuko Nakajima Hiroshi Yoshida Shiro Maeda 《Molecular Crystals and Liquid Crystals》2013,570(1):67-74
The second and fourth order parameters of nematic MBBA and 5CB have been determined near the nematic-isotropic transition temperatures by means of resonance Raman measurements on β-carotene dissolved as an orientational probe. The limiting behaviour of the second order parameter of MBBA near the transition point has been investigated on the basis of its fluctuation, which is deduced from the 2nd and 4th order parameter values. 相似文献
175.
J. Kroupa V. Bovtun D. Nuzhnyy M. Savinov P. Vanek S. Kamba 《Phase Transitions》2013,86(11-12):1059-1064
We investigated the grain size effect on the high temperature behaviour of PMN-35PT ceramics around the tetragonal–cubic phase transition using second harmonic generation (SHG) and dielectric spectroscopy. Our data revealed coexistence of the first-order ferroelectric phase transition and relaxor behaviour in the coarse grain (grain size ~4 µm) µ_PMN-35PT. The phase transition is hindered and relaxor features prevail in the fine grain (grain size ~150 nm) n_PMN-35PT ceramics. Effect of the grain-size reduction on the SHG and dielectric response could be attributed to stabilisation of intermediate domain configurations between the frozen polar nanoclusters and large ferroelectric domains and to the enhanced stability of polar nanoclusters in the fine grain ceramics. 相似文献
176.
Second harmonic generation and TANDEL effect studies on ferroelectric triglycine selenate and triglycine sulphate-Selenate
crystals near the Curie temperature indicate that the generated second harmonic is linear for low biasing fields with a zero
off-set, while it decreases sharply at higher biasing fields. In the autostabilized state, the TANDEL elements adjust their
impedance against the variation of a.c. field. The experiments on annealed crystals establish that the zero offset is due
to the internal bias that owes its origin to the defect structure. 相似文献
177.
An expression is obtained for the sound attenuation constant in a doped displacive ferroelectrics in the presence of an external
electric field, using double-time temperature-dependent Green’s function technique. The mass and force constant changes due
to impurity atoms, are taken into account along with higher order anharmonic and electric dipole moment terms, in the Silverman-Joseph
Hamiltonian. The attenuation constant increases with an external electric field. The soft mode is responsible for the anomalously
increasing behaviour of the attenuation constant in the vicinity of the Curie temperature. The results agree with those attained
by Tani and Tsuda and Heuter and Neuhaus. 相似文献
178.
J. Rutkowska P. Perkowski W. Piecek Z. Raszewski J. Kędzierski 《Opto-Electronics Review》2008,16(3):262-266
Dielectric measurements were performed for two smectogens, being structurally analogous with the opposite space orientation
of the-COO ester group in the molecular core, using a HP4192A impedance analyser. Gold coated electrode cells of different
thicknesses were used. Temperature dependences of the relaxation frequency fR and the inverse of the dielectric strength Δε′┴
−1 obtained by fitting experimental values of perpendicular components, i.e., the real ε′┴ and the imaginary ε″┴ parts of the complex dielectric permittivity to the Cole-Cole equation as well as the investigation of modification of relaxation
processes under bias were determined for the SmC*, SmA*, and N* phases of studied compounds. One can conclude, on the basis of the above results, that dielectric relaxation processes observed
by us in the studied compounds are similar to those of the soft and Goldstone mode typically observed by others in the SmC*, SmA*, and N* phases. It is concluded from acomparison of their properties with other related compounds that the link between the biphenyl
moiety and-COO ester group is closely related to the stability of smectic phases. 相似文献
179.
Rafał Sitko Beata Zawisza Jerzy Jurczyk Dariusz Bochenek Małgorzata Płoñska 《Mikrochimica acta》2004,144(1-3):9-15
A method of wavelength-dispersive XRF analysis of Pb(Zr,Ti)O3 type ferroelectric ceramics doped with Pb(Nb,Mn)O3 and Bi2O3 is presented. The major elements Pb, Zr, Ti and minor elements Nb, Mn, Bi were determined. Matrix effects were minimized by using the thin layer method. Standards of the same chemical composition but varied masses were prepared to simplify calibration. To minimize errors resulting from inhomogeneity of a mass per unit area, the internal standard was used. Preparation of the sample consisted in digesting 25mg of the materials (with nickel as the internal standard) in sulfuric acid, evaporating to dryness and digesting in nitric acid and hydrogen peroxide, filling up to 25mL, and dropping 0.5mL of the solution onto a substrate. Standard samples were prepared by dropping different amounts of the multielement solution onto the substrate. The residual standard deviation for the reference sample of mass from 0.25mg to 0.7mg was within the range of 0.001–0.009mg (correlation coefficient 0.998–0.999) for major elements and within the range of 0.00003–0.0009mg (correlation coefficient 0.989–0.993) for minor elements. The detection limits for 0.5mg samples were within the range of 0.015%–0.35% for manganese and zirconium, respectively. 相似文献
180.
D. Niznansky J. Plocek M. Svobodova I. Nemec J.-L. Rehspringer P. Vanek Z. Micka 《Journal of Sol-Gel Science and Technology》2003,26(1-3):447-451
The nanocomposites representing interesting H-bond compounds (Na3H(SO4)2, RbHSO4, RbHSeO4, and Rb3H(SeO4)2) in the silica matrix were prepared by the sol-gel method. Resulting samples were characterised by X-ray diffraction, IR spectroscopy and electron microscopy. Transition temperatures of the nanocomposites were determined using DSC and compared with the T
C of the pure bulk active compounds. The shifts of the T
C towards lower temperatures or the disappearing of the certain effects in the case nanocomposites were observed. A possible explanation of these phenomena was proposed using the analogy with the superparamagnetic compounds. 相似文献