Behaviour of the optical indicatrix and small‐angle light scattering in the case of “Devil's Staircase”

Sveleba, S. A.; Kapustianik, V.; Polovinko, I. I.; Bublyk, Myroslava; Zhmurko, V. S.

doi:10.1002/pssb.2221830125

Cited by 7 publications

(4 citation statements)

References 12 publications

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“…However, the authors did not take into account that the incommensurate phase symmetry point group coincides with the point group of the high-temperature parent phase which forbids appearance of the optical indicatrix rotation. Therefore, the results reported in [22][23][24] do not agree with the well--known statement of the macroscopic crystallophysics that the symmetry of crystal tensor properties is determined by its symmetry point group [25,26].…”

Section: Introductionmentioning

confidence: 62%

“…The optical indicatrix rotation has been observed in the set of experimental works [22][23][24]. However, the authors did not take into account that the incommensurate phase symmetry point group coincides with the point group of the high-temperature parent phase which forbids appearance of the optical indicatrix rotation.…”

Section: Introductionmentioning

confidence: 99%

“…However, they are the subgroups of the parent phase symmetry point group. Therefore, under given conditions one can expect the optical indicatrix rotation, especially, its non-monotonous temperature dependence [22]. The symmetry groups of commensurate phases are not the subgroups of each other and can coincide.…”

Section: Introductionmentioning

confidence: 99%

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Phase Transitions in [N(CH₃)₄]₂ZnCl₄and [N(CH₃)₄]₂CuCl₄Crystals Related with the Incommensurate Modulation Existence

et al. 2008

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The continuous phase transitions are observed in the crystals with incommensurate phase. They are transitions of parent-incommensurate phases (Ti); transitions between metastable states; incommensurate-commensurate phases (T c ). It was set that phase transition between parent and incommensurate phase is a continuous second-order phase transition with a critical index β = 0.5. The transition between metastable states is a continuous phase transition through the intermediate temperature region -incommensurate phase. The wave vector changes with the temperature here and wave vector q * = q 1 − q 2 appears, where q 1 , q 2 denote commensurate values of incommensurability wave vector of neighboring metastable states. It was shown that the phase transition between incommensurate and commensurate phases is a continuous phase transition.

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Section: Introductionmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

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Phase Transitions in [N(CH₃)₄]₂ZnCl₄and [N(CH₃)₄]₂CuCl₄Crystals Related with the Incommensurate Modulation Existence

et al. 2008

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“…4a) may be indicative of light scattering caused by a realignment of the superstructure during the passage from one metastable state into another. It is known [12] that the appearance of a superposition wave with a period greater than that of the light wave is accompanied by small angle light scattering. Under these conditions, the time variation in the temperature undergoes an anomalous spiky drop (Fig.…”

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Optical transmission coefficient of crystalline [N(CH3)4]2MeCl4 in the incommensurate phase

et al. 2011

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surate phase when a defect density wave is present. It is found that an anomalous reduction in the transmission coefficient is caused by scattering of light owing to a realignment of the superstructure during transitions between metastable states. When a defect density wave is present, the anomalous optical transmission of the crystal is related to the scattering of light on superstructure inhomogeneities produced by a superposition of existing modulation waves.Keywords: incommensurate phase, metastable state, optical transmission coefficient. Introduction.It has been shown [1] that the existence of superstructure in a crystal shows up through optical reflection and scattering. Light scattering in a dielectric is caused by optical inhomogeneities of the medium owing to fluctuations in its dielectric constant. The resulting incommensurate superstructure [1] disrupts the optical homogeneity of the crystal. Thus, the development of incommensurate modulation will be accompanied by the scattering of light.Phases with an incommensurate superstructure and periods greater than the interatomic distance, but less than the optical wavelength, have been discovered in a number of dielectrics. The shape of a modulation wave, which is mainly described as sinusoidal, has more complicated inflections, which are referred to as phase solitons. Impurities and defects affect the dynamics of the soliton system. Pinning on defects and impurities produces a number of universal properties in incommensurate phases, including hysteresis in the temperature dependences of the wave vector, thermal, dielectric, and thermo-optical memory effects, the kinetics of physical quantities, etc.The effect of defects on the modulated superstructure shows up most clearly when the soliton-defect interaction force becomes comparable to the soliton-soliton interaction force. This leads to the formation of multiwave states. Under these conditions the dynamics of the modulated superstructure is complicated and takes place through superposition of existing modulation waves.It is known that the optical effects owing to the superstructure are controlled by the ratio d/λ (d is the period of the superstructure wave and λ is the optical wavelength) [2, 3]. When d > λ, diffraction of a light beam is observed on the periodic superstructure formed by the superposition of existing spatial modulation waves [2, 4] (defect density waves and incommensurate modulation waves).Multiwave states of the superstructure in the incommensurate phase of a crystal originate in the spatial inhomogeneity of the crystal and may be accompanied by the scattering of light. Here we study the temperature and time behavior of the optical transmission coefficient of [N(CH 3 ) 4 ] 2 ZnCl 4 and [N(CH 3 ) 4 ] 2 CuCl 4 crystals with density defect waves (spatial structural deformation wave). It is known that when a crystal in the incommensurate phase is held at a constant temperature, the incommensurate superstructure relaxes to its equilibrium state. Since the time it spends in a metastable state ...

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Specific Sequence of Commensurate Long-Periodic Regions Inside the Incommensurate Phases

Sveleba

Kapustianik

Polovinko

et al. 1995

Phys. Stat. Sol. (a)

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The results of detailed investigations of dielectric constant, ϵb, and optical birefringence in betaine calcium chloride dihydrate are reported. The effect of bias electric field and uniaxial mechanical stress on the temperature range of localization of the incommensurate modulation wave vector k is observed. It is shown that the incommensurate phase consists of several long‐periodic commensurate (LPC) phases. Additional regions of incommensurability wave vector k localization are found. Some of the LPC phases are ferroelectric with spontantaneous polarization arising along a‐ or b‐axis and the other ones are ferroelastic with spontaneous strain Uxy. The temperature region of different LPC phase existence is changed under the influence of a corresponding external field. The observed sequence of LPC phases explains the availability of optical activity within the incommensurate phase.

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Behaviour of the optical indicatrix and small‐angle light scattering in the case of “Devil's Staircase”

Cited by 7 publications

References 12 publications

Phase Transitions in [N(CH₃)₄]₂ZnCl₄and [N(CH₃)₄]₂CuCl₄Crystals Related with the Incommensurate Modulation Existence

Phase Transitions in [N(CH₃)₄]₂ZnCl₄and [N(CH₃)₄]₂CuCl₄Crystals Related with the Incommensurate Modulation Existence

Optical transmission coefficient of crystalline [N(CH3)4]2MeCl4 in the incommensurate phase

Specific Sequence of Commensurate Long-Periodic Regions Inside the Incommensurate Phases

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Behaviour of the optical indicatrix and small‐angle light scattering in the case of “Devil's Staircase”

Cited by 7 publications

References 12 publications

Phase Transitions in [N(CH3)4]2ZnCl4and [N(CH3)4]2CuCl4Crystals Related with the Incommensurate Modulation Existence

Phase Transitions in [N(CH3)4]2ZnCl4and [N(CH3)4]2CuCl4Crystals Related with the Incommensurate Modulation Existence

Optical transmission coefficient of crystalline [N(CH3)4]2MeCl4 in the incommensurate phase

Specific Sequence of Commensurate Long-Periodic Regions Inside the Incommensurate Phases

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Phase Transitions in [N(CH₃)₄]₂ZnCl₄and [N(CH₃)₄]₂CuCl₄Crystals Related with the Incommensurate Modulation Existence

Phase Transitions in [N(CH₃)₄]₂ZnCl₄and [N(CH₃)₄]₂CuCl₄Crystals Related with the Incommensurate Modulation Existence