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121.
Irena Jankowska-Sumara 《Phase Transitions》2013,86(7):685-728
This paper is a review of earlier results which have been completed with recent investigations on the nature and sequence of phase transitions evolving in the antiferroelectric PbZr1–xSnxO3 single crystals (0 < x < 0.35). It was found that these crystals undergo several first-order phase transitions. To investigate these transitions, five experimental methods were used to characterize the crystal properties: birefringence, Raman light scattering, dielectric, thermodynamic and electromechanical methods, and the atomic force microscopy-piezoresponse force microscopy (AFM-PFM) method to focus also on nanoscale properties. Temperature dependencies have been tentatively measured in a wide range, including a region above TC, where precursor dynamics is observed in the form of non-centrosymmetric regions existing locally in crystal lattices.New experimental data (Raman light scattering and PFM) are presented mainly to revise the phase diagram and, at the same time, to complement other studies on the problem of pre-transitional effects. The phase transition mechanism in PbZr1–xSnxO3 is discussed taking into account the incommensurability of crystal lattices, ferroelastic behavior of multicell cubic phases, electric field influence on antiferroelectric to ferroelectric transformation, and flexoelectric effect. 相似文献
122.
An optical study of N-(p-n-alkyloxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds with the alkoxy chain number n?=?1, 3, 6, 7, and 10 has been carried out by measuring the refractive indices using modified spectrometer and direct measurement of birefringence employing the Newton's rings method. Further, the molecular polarizability anisotropies are evaluated using Lippincott δ-function model, the molecular vibration method, Haller's extrapolation method, and scaling factor method. The molecular polarizabilities α e and α 0 are calculated using Vuk's isotropic and Neugebauer anisotropic local field models. The order parameter S is estimated by employing the molecular polarizability values determined from experimental refractive indices and density data and the polarizability anisotropy values. Further, the order parameter S is also obtained directly from the birefringence data. A comparison has been carried out among the order parameter obtained from different ways and the results are compared with the body of the data available in the literature. 相似文献
123.
Abstract In this paper the results of birefringence studies and of optical observations in polarized light in a wide temperature region are presented for crystals Cs2CdI4 and Cs2ZnI4. There is the following sequence of phases: commensurate orthorhombic Pnma ? incommensurate ? monoclinic ferroelastic P21/n ? triclinic ferroelastic PT. A correlation was observed between the peculiarities of birefringence and NQR spectra temperature dependence. An assumption is made, that in Cs2ZnI4 crystal in a broad pre-transition region (T - T i = 100 K) precursor clusters exist, which manifest themselves as coexistence of NQR spectra of two phases and as deviation of birefringence from the linear temperature dependence (“tail”). 相似文献
124.
We investigate the adiabatic and dynamical natures of the lattice relaxation of excitons in strongly coupled electron-phonon (e-ph) systems using the extended Peierls-Hubbard model, so as to clarify the possible mechanisms of the photoinduced structural phase transition (PISPT) via multi-photon. Focusing on the growth process of relaxed domains that is induced by multi-photoexcitation, we calculate the adiabatic potential energy surfaces relevant to the nonlinear lattice relaxations of excitons in this process. Calculated potentials lead to an essential model of a multi-stepwise potential-crossing (MSPC) system that is composed of many displaced harmonic oscillators as an elementary process of the domain growth in the strongly coupled e-ph systems. We also investigate the dynamical natures in such MSPC systems calculating the time-developments the excited wave packet in this system using the density operator. It is concluded from calculated results that the system possibly develops from the lowest-energy potential state to the higher ones by the effect of the photoexcitations followed by the lattice relaxations. 相似文献
125.
Tetsuo Ogawa 《Phase Transitions》2013,86(1-2):93-128
Photoinduced structural phase transitions via excited electronic states are discussed theoretically using a one-dimensional model composed of localized electrons and lattices under the adiabatic or diabatic approximation. We show that the global structural change by photoexcitation only at a site is possible, and we clarify conditions for the occurrence of such phenomena. Spatiotemporal dynamics of nonequilibrium first-order phase transitions is also investigated in detail in terms of photoinduced nucleations and domino processes of the domain boundaries (domain walls), which are in striking contrast to the mean-field dynamics. In the adiabatic regime, after the spontaneous emission of a photon, an initial local structural change (i) remains locally, (ii) induces cooperatively a global structural change, or (iii) disappears and returns to the initial phase. Dynamical features of the case (ii) are characterized by the deterministic (semichaotic) domino process; domain walls between the two phases move determinis-tically at a constant velocity (with changing speed) without further spontaneous emissions in the case of strong (weak) dissipation. In the diabatic regime, similar three types of structural change exist. The domain-wall dynamics is described as the stochastic domino process, which is accompanied by the successive radiative transitions. A new theoretical treatment is also proposed to study crossover between the adiabatic and diabatic regimes. 相似文献
126.
Yutaka Koike 《Journal of Macromolecular Science: Physics》2013,52(1):13-37
The uniaxial deformation behavior of three polypropylene films with isotacticity indices varying from 43 to 95 was investigated in the partially molten state using real time, true stress, true strain, and birefringence measurement system. These polymers generally exhibit three regime stress‐birefringence behaviors during stretching. The unmelted crystalline regions act as physical junctions. If the films contain crystallinity that is too low (less than ca. 10%) the Regime I disappears. Under these conditions, the films were found to exhibit large linearity in strain and stress optical behavior. If, however, too low a deformation rate is employed, these relationships become non‐linear. The increase of isotacticity increases the magnitude of the birefringence at all deformation levels primarily as a result of the increase in crystallinity that helps in establishing a long‐range physical network. This increase in the long‐range connectivity was found to promote not only the orientation in crystalline domains but also in the amorphous domains. The increased long‐range connectivity in high isotacticity films was also found to result in destruction of local initial structures that generate a large fraction of the oriented amorphous chain regions. This translates into larger stress decrease and birefringence increase changes during the holding stage where the oriented amorphous chains undergo complex relaxation/oriented crystallization processes. 相似文献
127.
Ch. Y. Gao H. R. Xia J. Q. Xu Sh. Ch. Si H. J. Zhang J. Y. Wang 《Crystal Research and Technology》2008,43(4):443-446
The birefringence of (Ca0.28Ba0.72)0.75(Sr0.60Ba0.40)Nb2O6 crystal is measured basing on polarization‐ extinction method and conoscopic interference method. Experimental results show that the birefringence in this crystal is up to 10‐5, the natural birefringence in this crystal is (no ‐ne) = 5.89 x 10‐5 with the He‐Ne laser wavelength at 632.8nm and the birefringence grads with wavelength at 532nm is 5.68 x 10‐5, which indicate the good optical homogeneity of this crystal. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
128.
P. Muthu Chidambara Nathan N. Kalyanasundaram D. Ravikumar 《Fiber and Integrated Optics》2008,27(2):99-111
In this article, the propagation of solitons in a single mode fiber with polarization mode dispersion (PMD) is analyzed. In optical fibers, the randomly varying birefringence degrades soliton transmission system in two aspects. First, the dispersive waves cause pulse broadening. Second, the dispersive waves interact with other soliton pulses. Here we studied the effects of PMD on a single pulse and the variation of pulse broadening, energy decay, and degree of polarization on a single soliton pulse propagating over a very long distance. 相似文献
129.
Benjamin Y. Ku Mei-Lin ChanZhiya Ma David A. Horsley 《Journal of magnetism and magnetic materials》2008
Optical detection of the frequency-dependent magnetic relaxation signal is used to monitor the binding of biological molecules to magnetic nanoparticles in a ferrofluid. Biological binding reactions cause changes in the magnetic relaxation signal due to an increase in the average hydrodynamic diameter of the nanoparticles. To allow the relaxation signal to be detected in dilute ferrofluids, measurements are made using a balanced photodetector, resulting in a 25 μV/√Hz noise floor, within 50% of the theoretical limit imposed by photon shot noise. Measurements of a ferrofluid composed of magnetite nanoparticles coated with anti-IgG antibodies show that the average hydrodynamic diameter increases from 115.2 to 125.4 nm after reaction with IgG. 相似文献
130.
声各向同性的金属材料在应力作用下表现出声各向异性,这是用声弹性法分析材料内部应力的基础。本文用偏振方向平行或垂直于应力方向的超声纯横波对LY11型铝合金进行测试。实验结果表明:材料在拉、压单轴应力作用下,偏振方向平行和垂直于应力方向的超声纯横波的声速都发生了变化。实验在分析材料声各向异性的基础上计算材料声弹性双折射系数,得到测试LY11型铝合金内部应力的理论公式,并对其内部的残余应力进行评估。实验中利用双换能器回振法测量声速,时间测试精确度可达10-11s,可精确测量声速的微小变化量。 相似文献