THE FEATURES OF CONDUCTION ANISOTROPY OF INTERCALATED LAYERED (original) (raw)
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Anisotropic properties and conduction mechanism of TlInSe2 chain semiconductor
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The effect of thermal annealing on dark conductivity and thermally stimulated conductivity in ferroelectric-semiconductor TlGaSe 2 within the incommensurate phase is investigated. It is shown that both types of conductivities are drastically changed after annealing of the crystal for some hours within the incommensurate phase. The results obtained lead to the conclusion that the main effect of annealing is a large decrease of impurity capture cross sections leading to the dramatic increasing of relaxation times.
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Anisotropic two-dimensional materials possess intrinsic angle-dependent physical properties that originate from their low crystal symmetry. Yet, how these properties are affected by external impurities or structural defects in the material is still wholly unclear. Here, we address this question by investigating the electrical transport in the anisotropic layered model system germanium arsenide. First, we show that the ratio of conductivities along the armchair and zigzag crystallographic directions exhibits an intriguing dependence with respect to both temperature and carrier density. Then, by using a conceptually simple model, we demonstrate that this unexpected behavior is directly related to the presence of impurityinduced localized states in the band gap that introduce isotropic hopping conduction. The presence of this conduction mechanism in addition to the intrinsic band conduction significantly influences the anisotropic electrical properties of the material, especially at room temperature, i.e., at application-relevant conditions.
Band gap exciton in ferroelectric TlInS 2 : Dimensionality and screening
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This work reports two-dimensionality of band-gap exciton in layered ferroelectric TlInS 2 , accessed by spectroscopic phase modulated ellipsometry in a wide range of temperatures embracing normal, incommensurate, and commensurate phases of this material. A significant decrease in exciton binding energy is observed upon approaching the temperature region of the incommensurate phase on cooling or heating. The effective static rather than optic dielectric screening is shown to be responsible for the observed behavior of exciton binding energy that remains larger than the energy of the longitudinaloptical phonon at all accessed temperatures. The temperature dependence of this screening is remarkable in that it obeys Currie-Weiss law. The values of the exciton's reduced mass and three-dimensional effective Bohr radius are obtained. The former keeps constant to be 0.928 the mass of the free electron while the latter irregularly changes with temperature, remaining within 14-19 Ålimits. The last values correspond to the doubled thickness of a single layer.
Effect of electric field on negative linear expansion of ferroelectric-semiconductor TlGaSe[sub 2]
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The effect of electric field on the thermal expansion of the TlGaSe 2 ferroelectric-semiconductor with a layer crystalline structure has been investigated. A strong transformation of negative linear expansion coefficient in the layer plane has been observed as a result of the applied electric field. It was concluded that internal electric fields created by local polarized states in the ferroelectricsemiconductor are responsible for a negative thermal expansion and its behavior under the electric field. Predominantly, the electrostriction effect is the driving mechanism of the lattice deformation of TlGaSe 2 crystals at low temperatures.
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Physica B: Condensed Matter, 2017
Dielectric hysteresis loops of pure and lanthanum doped TlInS 2 ferroelectricsemiconductors were studied at the frequency 50 Hz for different temperatures below the Curie temperature (ܶ). It has been revealed that, without any poling procedure, pure TlInS 2 exhibits normal single hysteresis loops at ܶ < ܶ. After electric field-cooled treatment of TlInS 2 the shape of hysteresis loops was strongly affected by corresponding charged deep level defects which were previously activated during the poling process. As a result, an additional defect polarization state from space charges accumulated on the intrinsic deep level defects has been revealed in pure TlInS 2 at the temperatures below ܶ. Besides, unusual multiple hysteresis loops were observed in La doped TlInS 2 at ܶ < ܶ after application of different external perturbations (electric field, exposition and memory effect) to the sample. Measurements of the hysteresis loops in TlInS 2 :La revealed the slim single, double and even triple polarizationelectric field (P-E) hysteresis loops. This intriguing phenomenon is attributed to the domain pinning by photoand electrically active Laimpurity centers. The temperature variation of double-hysteresis loop was also investigated. Due to the heat elimination of the random local defect polar moments, the doublehysteresis loops were transformed into a normal single hysteresis loops on increasing the temperature.
Structure of Interfaces in Layered Ferroelectrics of First and/or Second Order Transition
Journal of the Physical Society of Japan, 2004
We studied the structure of interfaces in layered ferroelectrics comprising two different ferroelectric materials with first and/or second order transitions. The layered structure is described using the Landau-Ginzburg theory by including a bilinear coupling at the interface between the two neighboring layers. The interfacial coupling leads to the variation of polarization across the interface from one layer to another. An abrupt or continuous change of polarization across the interface is found to depend on the strength of coupling. For a layered structure having a layer in paraelectric phase, an interface-ordered state is predicted (in the paraelectric layer) as a manifestation of interfacial coupling. The Tilley-Zeks model is compared with the present approach to discuss the relationship between the bilinear coupling parameter and the extrapolation lengths.