Search results for "ferroelectric"
showing 10 items of 374 documents
Forming pressure dependence of the ferroelectric domain structure in green barium titanate pellets
1995
Abstract Modifications of the X-ray diffraction line profiles by die pressing of fine grained powders of barium titanate have been studied. Two main parameters have been considered: the forming pressure and the mechanical characteristics of the binder. The higher the forming pressure, the greater the modifications of the line profiles. Furthermore, the phenomena seems to be related to pressing only; no significant effect related to the nature of the binder has been shown. The modifications of the diffraction line profiles are interpreted by considering a reduction of the size of the ferroelectric domains during pressing. In order to confirm this interpretation, the behaviour of the domain s…
Quantum chemical calculations of KTN solid solutions
1998
Abstract The results of semi-empirical calculations for perovskite KNbxTa1−xO3 (KTN) solid solutions are presented for x = 0.04, 0.11, 0.89, and 0.96. Quantum chemical method of the Intermediate Neglect of the Differential Overlap (INDO) was combined with 135- and 320-atom supercells. Analysis of the optimised atomic and electronic structure has clearly demonstrated that several nearest Nb atoms substituting for Ta in KTaO3 — unlike Ta impurities in KNbO3 — reveal the self-ordering effect, which probably triggers the ferroelectricity observed in KTN.
The influence of quantum fluctuations on phase transition temperature in disordered ferroelectrics
2014
We consider the disordered ferroelectric, where the impurity dipoles interact via quantum optical phonons. We show that quantum fluctuations are amplified by the effects of disorder so that they can be important up to the ferroelectric phase transition temperature. In this paper, we calculate the ferroelectric phase transition temperature as a function of impurity dipole concentration. We show that quantum effects change the character of concentrational dependence of . Namely, they cause the discontinuity in so that the critical concentration is reached abruptly. We have shown that quantum effects inhibit the ferroelectricity so that larger (than that in purely classical disordered ferroele…
Dynamics of Phase Transition in 0.4NBT-0.4ST-0.2PT Solid Solution
2012
In this paper we present dielectric spectroscopy results of NBT-(0.6-x)ST-xPT with x = 0.2 solid solution. Dielectric investigations clearly showed a relaxor—normal ferroelectric phase transition at TPT = 419 K and low temperature and low frequency dispersion similar to coexistence of dipolar glass and ferroelectric phase. The mean relaxation time above the phase transition follows Vogel—Fulcher law with following parameters: E A = 0.179 eV, τ 0 = 3.39·10−14 s, T VF = 223 K.
Parametric self-trapping in the presence of randomized quasi phase matching
2010
We report on experimental evidence of parametric spatial solitons in a quadratic crystal with randomized periodic ferroelectric poling. Two-color self-focusing via quadratic cascading overcomes the diffractive nature of both fundamental and frequency-doubled beams.
Integrated frequency shifter in periodically poled lithium tantalate waveguide
2010
A frequency shifting device is fabricated and tested in a ferroelectric waveguide in a low-photorefractivity crystal. Periodic poling for quasi-phase-matching and channels for operation in the near-infrared C-band were obtained in congruent lithium tantalate, demonstrating for the first time both wave confinement and two-stage parametric conversion in such waveguides.
Free Charge Carriers in Mixed Valency Oxides as Possible Mediators of Magnetoelectric Effect
2009
We show, that in a substance with mixed-valence ions, which can supply free carriers and have electric dipole and spin moments, three types of long-range order (ferromagnetic, ferroelectric and magnetoelectric (ME)) can occur at low temperatures. The origin of the effect is that free charge carriers can mediate the multiferroic behavior via spin – spin (RKKY), dipole-dipole and dipole - spin interactions. We show that there is an optimal carrier concentration, at which the strength of ME interaction is maximal and comparable to that of RKKY interaction. Our analysis shows that disorder and finite conductivity in the above substances does not suppress multiferroic effects.
Transition probabilities of PrII-lines emitted from a ferroelectric plasma source
1991
Abstract An argon-praseodymium plasma was generated under atmospheric pressure between a ceramic ferroelectric plate and a praseodymium plate. The system of plates was connected to an acoustic frequency supply. The plasma radiation was analyzed in the spectral range from 2000 to 7000 A by using a grating spectrograph with a linear dispersion near 1 mm/A, adopted to photoelectric measurements. The emission spectrum of praseodymium was recorded and the intensities of a few hundred lines were measured. Transition probabilities were determined for 62PrII-lines, using available lifetime data for excited levels and measured branching ratios of the corresponding lines. Reasonable agreement has bee…
Thickness Dependence of Random Field Distribution in Thin Films Made of Disordered Ferroelectrics
2005
Abstract We present the calculation of first moment E 0 and variance ΔE of distribution function of random fields in a ferroelectric of finite size. Specific calculations have been performed for the case of slab-shaped ferroelectric thin film. We have shown that E 0 and ΔE can be expressed through the integrals from first and second degree of Green's function of ferroelectric in k-space. To obtain the Green's function, we solve the differential equation minimizing Landau free energy of a ferroelectric with respect to the boundary conditions on its surfaces. We show that both E 0 and ΔE depend on film thickness L.
Molecular dynamics in low-molar and polymeric ferroelectric liquid crystals
1991
Broadband dielectric spectroscopy covering the frequency range from 10−1 Hz to 109 Hz was employed to study the molecular dynamics in low-molar and polymeric ferrroelectric liquid crystals. At frequencies below 106 Hz the ferroelectric modes, soft and Goldstone mode are observed. In the frequency regime from 106 Hz to 109 Hz a fast relaxation process is found, which is assigned to the hindered rotation of the mesogens around their long molecular axis. It turns out that the molecular dynamics is not principally different between low-molar and polymeric systems.