Dielectric constant and EPR spectra of Fe doped TlInS2 crystal near the structural phase transitions (original) (raw)
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Dielectric susceptibility behaviour in the incommensurate phase of TlInS2
Physica B: Condensed Matter, 2003
Peculiarities of the temperature behaviour of the dielectric susceptibility of TlInS 2 in the temperature interval of incommensurate (IC) phase have been theoretically investigated on the basis of recently suggested two-sublattice model of the phase transitions in TlInS 2 , which is based on the hypothesis about the coexistence of improper and proper ferroelectricity and also the presence of type I and type II incommensurations in the same compound. The temperature dependence of the dielectric constant of TlInS 2 in the IC phase was calculated. An agreement between theoretical and experimental results has been obtained.
Dielectric susceptibility behaviour in the incommensurate phase of TlInS< sub> 2
2003
Peculiarities of the temperature behaviour of the dielectric susceptibility of TlInS 2 in the temperature interval of incommensurate (IC) phase have been theoretically investigated on the basis of recently suggested two-sublattice model of the phase transitions in TlInS 2 , which is based on the hypothesis about the coexistence of improper and proper ferroelectricity and also the presence of type I and type II incommensurations in the same compound. The temperature dependence of the dielectric constant of TlInS 2 in the IC phase was calculated. An agreement between theoretical and experimental results has been obtained.
EPR study of the structural phase transitions in Fe3+ doped TlInS2
Physica Status Solidi (a), 2006
The results of low temperature EPR investigations of Fe doped TlInS2 single crystals in the temperature range 5–300 K are presented. The EPR signal due to Fe3+ centers located at the centers of InS4 tetrahedrons has been observed. It has been established that the resonance lines exhibit a slight shift and remarkable splitting at the temperatures lower than 200 K, which is attributed to the effect of the ferroelectric phase transition. The rotational patterns of the resonance fields reveal a doubling of the number of centers at low temperatures. The preliminary simulation indicates that the doubling is related to the rotation of the principal axis system of the centers, while the magnitude of fine structure splitting is nearly the same. ( © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Thin Solid Films, 2008
Temperature-dependent change in core-level electronic structures of the layered semiconductor-ferroelectric TlInS 2 with incommensurate phase has been investigated by means of X-ray photoemission spectroscopy. The temperature dependence of the relative peak position for each core level (Tl 4f, In 3d and S 2p) is found to differ very much in the regions bordering each other at the normal-incommensurate phase transition point of 218 K. The obtained data suggest that the charge distribution in TlInS 2 dramatically changes upon passing from the normal phase (T N 218 K) to the spatially modulated incommensurate phase (T b 218 K).
Dielectric Properties of TlInS2 with FeSe2 Admixture. Influence of an External Electric Field
Physica Status Solidi (a), 1993
The results of the investigation of the influence of external electric field and FeSe, admixture on the dielectric properties of the incommensurate ferroelectric TIInS, are presented. It is shown that changes of the static dielectric permittivity by impurities or external electric field can be explained by the model of coupled phason and amplitudon. The increase of the coupling constant by impurities or electric field leads to the appearance of a maximum of dielectric permittivity in the middle of the incommensurate phase and changes the value of the static permittivity. Der EinfluD eines elektrischen Feldes und von Beimischungen von FeSe, auf d?? dielektrischen Eigenschaften des inkommensurablen Ferroelektrikums TlInS, wird untersucht. Anderungen der statischen Dielektrizitatskonstante mit der Beimischung und dem auDeren elektrischen Feld konnen mittels eines Modells gekoppelter Phasonen und Amplitudonen erklart werden. Die VergroDerung der Kopplungskonstante durch Beimischungen oder elektrische Felder fuhrt zu einem Maximum der Dielektrizitatskonstante in der Mitte der inkommensurablen Phase und verandert die GroDe der statischen Dielektrizitatskonstaute.
Polarization switching in undoped and La - doped TlInS 2 ferroelectric - semiconductors
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.
Structural phase transitions in Fe 3+ -doped ferroelectric TlGaSe 2 crystal
Solid State Communications, 2008
This paper presents the results of dielectric constant and Electron Paramagnetic Resonance (EPR) investigations of Fe 3+ -doped TlGaSe 2 single crystals in the temperature range of 15-300 K. The influence of Fe impurities on dielectric properties and phase transitions of TlGaSe 2 crystal has been studied. The results were considered in comparison with earlier observed results from pure TlGaSe 2 compounds. We observed the considerable decrease of the dielectric constant as well as the change of the shape of the temperature dependence of the dielectric constant in doped crystals. Some certain significant changes of EPR spectra, which are associated with a strong splitting and appearance of additional resonance lines, were observed at the temperatures below 110 K. Such transformations are considered as the result of non-equivalent displacements of different groups of Tl atoms during the structural phase transitions.
Dielectric spectroscopy and nonequilibrium phase transitions in TlGaSe 2 layered crystals
Semiconductor Science and Technology, 2007
The real and imaginary parts of the dielectric function of TlGaSe 2 single crystals are investigated in the frequency range 30 Hz-13 MHz and at temperatures 80 K-300 K. A low frequency dispersion due to the interfacial polarization within the crystals is observed. The temperature dependence of relaxation time is obtained in a wide temperature region. A welldistinguished anomalous rise of relaxation time has been established in the 145 K-190 K temperature range for the first time far from the traditional phase transitions known in TlGaSe 2 crystals. It is shown that the observed behaviour of relaxation time is due to instabilities in the electronic subsystem revealing themselves as a non-equilibrium phase transition. A close relationship between the observed anomaly and anomalous behaviour of the various physical parameters of the investigated crystals is proposed.
Temperature dependence of dielectric function and optical transitions in TlInSe2 and TlGaTe2
Thin Solid Films, 2011
The principal components of the dielectric function of TlInSe 2 and TlGaTe 2 crystals with quasi-onedimensional chain structure have been studied over the photon energies 1.5-5.0eV in the temperature range 140-400 K, with due regard to the reported phase transitions. For TlGaTe 2 , the absolute values of the dielectric function experience a sudden temperature-induced change at 290 K in nearly all the accessed photon energy range. The energy and other parameters of the critical points for inter-band optical transitions related to the obtained dielectric function have then been retrieved for both TlInSe 2 and TlGaTe 2 . An abrupt change in the energy of the critical point, positioned at 2.93 eV at room temperature and formed by optical transitions induced by the light polarized along the chains, has then been disclosed for TlGaTe 2 at 290 K.