Search results for "Optica"
showing 10 items of 7696 documents
Depolarization Field and Properties of Thin Ferroelectric Films with Inclusion of the Electrode Effect
2005
The influence of metallic electrodes on the properties of thin ferroelectric films is considered in the framework of the Ginzburg-Landau phenomenological theory. The contribution of the electrodes with different screening lengths l s of carriers in the electrode material is included in the free-energy functional. The critical temperature T cl , the critical thickness of the film, and the critical screening length of the electrode at which the ferroelectric phase transforms into the paraelectric phase are calculated. The Euler-Lagrange equation for the polarization P is solved by the direct variational method. The results demonstrate that the film properties can be calculated by minimizing t…
Electrical transport with temperature-induced spin disorder in NiMnSb
2019
Abstract We investigate theoretically the combined effect of phonons and magnons caused by finite temperatures on the electrical resistivity of nonstoichiometric half-Heusler NiMnSb alloy. The coherent potential approximation within the alloy analogy model is employed for an efficient treatment of chemical impurities, atomic displacements, and magnetic disorder. Spin fluctuations of local Mn moments are described by two models: (i) uncompensated disordered local moment approach and (ii) tilting of the moments. The calculated resistivity agrees with experimental data, the agreement is good up to 600 K. We show that a strong magnetic disorder leads to a violation of the Matthiessen’s rule for…
Thermodynamic properties at the phase transition of Pb(Zr, Sn, Ti)O3solid solutions
2000
Abstract Field induced deformation and electrocaloric effect are investigated in the vicinity of phase transition at 163°C. The sharp increase of electrostriction below Tc is explained by the field induced ferroelectric to antiferroelectric phase transition. The antiferroelectric phase appears and remains stable below Tc in the absence of field. Elastic compliance and thermal expansion as functions of temperature are studied.
Relation between deformation and polarization in the region of diffused phase transition of plzt 8/65/35
1995
Abstract The deformation as a function of polarization was measured in PLZT 8-10/65/35 in the region of diffused phase transition. A different behaviour of deformation in the region of double hysteresis loops was observed corresponding to ferroelectric and nonpolar phases as well as to the field induced phase transition region. In the ferroelectric phase the results are described by electrostriction. The decrease of volume as well as small longitudinal deformations at the field induced transition to ferroelectric state are explained by large remanent deformations, existing in the nonpolar phase. Since description of deformation in the framework of electrostriction cannot be motivated in the…
Experimental evidence for a local disorder in pure and doped perovskites
1992
Abstract In the soft mode picture, the ferroelectric phase transitions in most of ABO3 perovskites are triggered by the long wavelength oscillations of the B ions against their oxygen cage. There is now a lot of experimental evidence that this picture is incomplete. An extra contribution has to be included in the dynamical response. This contribution is usually thought to arise from local lattice distorsions; this is what will be called local disorder. A complete understanding of this local disorder requires the experimental determination of the microscopic origin, of the dynamics and spatial extension of the lattice distorsions. A useful way to summarize these requirements is to use the co…
Phase transitions of Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)O3ceramics
2001
Abstract The dielectric, elastic and electromechanical properties, electrocaloric effect and thermal expansion of poled and depoled Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)O3 samples are presented to evaluate the nature of polar phases existing in the solid solution above room temperature. The Kittel's free energy expansion is used to explain some essential features of physical properties.
Iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties
2013
The present work reports on the new soft ferromagnetic Heusler phases Fe${}_{2}$NiGe, Fe${}_{2}$CuGa, and Fe${}_{2}$CuAl, which in previous theoretical studies have been predicted to exist in a tetragonal Heusler structure. Together with the known phases Fe${}_{2}$CoGe and Fe${}_{2}$NiGa these materials have been synthesized and characterized by powder x-ray diffraction, ${}^{57}$Fe M\"ossbauer spectroscopy, superconducting quantum interference device, and energy-dispersive x-ray measurements. In particular M\"ossbauer spectroscopy was used to monitor the degree of local atomic order/disorder and to estimate magnetic moments at the Fe sites from the hyperfine fields. It is shown that in con…
Exact and Variational Treatment of Ferroelectric Thin Films with Different Materials of Electrodes
2005
We trace the influence of metallic electrodes on the properties of thin ferroelectric films. This has been done in the framework of the phenomenological Landau theory. We present both exact analytical solution of the problem in terms of Weierstrass elliptic functions and the variational solution. We calculate polarization, dielectric susceptibility, pyroelectric coefficient and depolarization field. We have shown that the ferroelectric phase of the film can be destroyed by the choice of material of electrodes with screening length exceeding some critical value. This demonstrates that we can control the physical properties of thin ferroelectric films by the proper choice of the electrode mat…
Algebraic value of the electrooptic coefficients and nature of charge carriers in batio3single crystals
1989
Abstract Some monodomain pure and Fe doped barium titanate monocrystals are studied. The algebraic values of the electrooptic coefficients r 13 and r 33 are evaluated using an interferometric method. Then, from energy transfer results it is possible to conclude that majority carriers are positive charges in all the samples.
Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays.
2022
Exciton transport in most organic materials is based on an incoherent hopping process between neighboring molecules. This process is very slow, setting a limit to the performance of organic optoelectronic devices. In this Article, we overcome the incoherent exciton transport by strongly coupling localized singlet excitations in a tetracene crystal to confined light modes in an array of plasmonic nanoparticles. We image the transport of the resulting exciton–polaritons in Fourier space at various distances from the excitation to directly probe their propagation length as a function of the exciton to photon fraction. Exciton–polaritons with an exciton fraction of 50% show a propagation length…