Characteristics of photoconductivity in thallium monosulfide single crystals

This work elucidates the photoconductivity (PC) of thallium monosulfide single crystals. Results are obtained in the 77–300 K temperature range, 1500–4500 V lx excitation intensity, 6–18 V applied voltage, and in the 640–1500 nm wavelength range. Both the ac-photoconductivity (ac-PC) and the spectral distribution of the photocurrent are studied in different values of light intensity, applied voltage and temperature. Dependencies of carrier lifetime on light intensity, applied voltage and temperature are also investigated as a result of the ac-PC measurements. The temperature dependence of the energy gap width was described by studying the dc-photoconductivity (dc-PC).      

Vibrational properties of crystals with TlSe type structure

The lattice vibration spectra of TlS and TllnSe₂ crystals were investigated by infrared reflectivity in the wavenumber range from 20 to 5000 cm^?1. The frequencies of K = 0 phonons were determined by Kramers-Kronig analysis of the spectra. All five infrared active lattice vibrations predicted by the group theoretical analysis were identified. The normal coordinates of vibrations for five infrared active phonons were determined. In the approximation which does not take into consideration long range Coulomb interaction values of the force constant and effective changes are obtained for TlSe, TlS and TllnSe₂ crystals.     

Magnetic properties of single crystals of the Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S solid solutions (0 ≤ <Emphasis Type="Italic">x</Emphasis> < 0.3)

The Cr _x Mn_{1 − x} S single crystals have been synthesized based on manganese monosulfide as a result of cation substitution, and their magnetic properties have been studied. It has been established that the Cr _x Mn_{1 − x} S solid solutions with a face-centered cubic NaCl structure are formed in the concentration region 0 ≤ x < 0.3. The unit cell parameter of the solid solution decreases as the degree of substitution increases due to the variation in the ionic radius of cations. These substances are antiferromagnets. An increase in the degree of cation substitution in the Cr _x Mn_{1 − x} S solid solutions is accompanied by a decrease in the number of 3d electrons in the d shell of manganese monosulfide and causes a decrease in the magnetic transition temperature from 149 K (x = 0) to 96 K (x = 0.29), which differs from previously known results.     

Heat capacity and thermal conductivity of Fe x Mn1 − x S single crystals

This paper reports on the results of investigations of the thermal properties and thermal conductivity of single crystals of homogeneous solid solutions Fe _x Mn_{1 ? x} S with a cubic NaCl structure, which have been prepared by the cation substitution for divalent manganese ions in manganese monosulfide. It has been revealed that the heat capacity and thermal conductivity exhibit anomalies in the range of the magnetic transition. The cation substitution is accompanied by an increase in the phase transition temperature.     

Theoretical analysis of the effect of crystallization temperature on structure formation in flexible-chain polymers

Theoretical analysis of flexible-chain polymer crystallization was carried out over a wide temperature range from glass transition temperature T_g to melting temperature T_m. Temperature dependence of dynamic behavior manifesting in the decrease of crystallizing length with decreasing temperature was taken into account. The dependence of crystallizing length on temperature was obtained using chosen values of it at T_g and T_m. The crystallization with the formation of folded-chain crystals (type I) and uncoiled-chain crystals (type II) was considered. The analysis of thermodynamical favorability of both types of crystals with respect to temperature made it possible to obtain a flexible-chain crystallizing polymer phase diagram. This diagram shows the existence of two ranges where type II crystal formation is more favorable: a narrow range near T_m and the wider one near T_g, separated by the temperature range of crystallization with chain folding. Temperature dependences of type II crystals fraction in the system and their size were calculated. It is shown that the crystallization at considerable supercooling leads to the appearance of a great number of type II small crystals connected by tie chains. The system formed is characterized by a high degree of crystallite interconnection.     

Investigation of the temperature dependences of the electrical resistance of SmS single crystals at different pressures

The pressure-induced shift of impurity levels under hydrostatic pressure at T = 300 K (−9.6 meV/MPa) has been obtained from measurements of the temperature dependences of the electrical resistance of SmS single crystals at different pressures. The obtained value confirms the validity of the existing model of the semiconductor-metal phase transition in samarium monosulfide.     

X-ray studies of the semiconductors snas,InTe, TlS and TISe UP TO 43 GPa

Abstract

The structures of the semiconductors SnAs, InTe, TlS and TlSe have been investigated using high-pressure (HP) diffraction technique-a gasketed diamond anvil cell (DAC)'. The pressure was measured by ruby fluorescence technique. The first order reversible transition from NaCl to CsCl structure was found in SnAs with volume discontinuity 5% the two-phase area extends from 32 to 43 GPa. The volume change V/v,(P) of the SnAs is shown in Figure 1. In agreement with the gomology rule3, the same pressure effect has been found in Sn_xSb1?x atP=9 GPa2.     

Specific features of the formation of the ferroelectric phase in polytypes of TlGaSe2 crystals

The polytypism of layered crystals of thallium gallium diselenide TlGaSe₂ has been found to substantially affect the temperature of phase transformations and the mechanism of formation of the polar state in these ferroelectrics. In particular, it is shown that the phase transition observed in the C-TlGaSe₂ polytype is an improper ferroelectric phase transition occurring at a temperature T _c ≈ 108 K, whereas the phase transition observed in the 2C-TlGaSe₂ polytype is a proper ferroelectric phase transition occurring at a higher temperature T _c ≈ 111 K. It is concluded that the elucidation of the polytype of a particular sample is a necessary stage of investigation of the TlGaSe₂ crystals.     

Properties of a new ferroelectric crystal family: MCd(NO2)3 [M=NH4, K,Rb, Cs,Tl]

Single crystals of MCd(NO₂)₃, with M=NH₄, K, Rb, Cs, and Tl, respectively, were grown and investigated by means of optical and dielectric methods. The crystals show rhombohedral symmetry (possible space group R 3) and multi-domain patterns at ambient temperature. The compounds exhibit phase transitions above room-temperature of first (M=K) and second order (M=Rb, Cs, Tl), respectively, into cubic high-temperature phases. Observed dielectric anomalies and hysteresis loops point to ferroelectric properties and suggest a relaxational order-disorder mechanism of the nitrite ions to be responsible for the transitions. The MCd-(NO₂)₃-compounds are seen to represent a new family of ferroelectrics with a cubic prototypic phase closely related to the structural type of the perovskites. The transions are classified by symmetry considerations, and a possible structure of the cubic high-temperature phase with space group Pm3 is proposed.     

On the relation between the gap,the transformation temperature and the average heat of atomization of As2Te3 glasses

The average heat of atomization of semiconducting glasses on the As₂Te₃ base, containing silicon, germanium and thallium is calculated from the heats of atomization of constituting elements. The average heat of atomization is correlated with the intrinsic energy gap and the transformation temperature of the studied glasses. The linear dependence between the energy gap, the transformation temperature and the average heat of atomization is found for As₂Te₃ glasses with silicon, germanium and thallium and is correlated with the binding energy between the constituting atoms.     

Structural,optical, and electrical properties of tin sulfide thin films grown with electron-beam evaporation

The effect of growth temperature on the phase evolution and morphology change of tin sulfide thin films by electron-beam evaporation was investigated. Orthorhombic tin monosulfide (SnS) was dominant at low growth temperature of 25 °C, whereas a sulfur-rich phase of Sn₂S₃ coalesced as the growth temperature increased over 200 °C. Thin film growth ceased at 280 °C due to re-evaporation of the tin sulfide. The dependence of growth temperature on the phase evolution of tin sulfide was confirmed by X-ray diffraction, scanning electron microscopy, and UV–Vis spectrophotometry. The lowest electrical resistivity of ∼51 Ω cm, with a majority hole concentration of ∼10¹⁷ cm⁻³, was obtained for the film grown at 100 °C, and the resistivity drastically increased with increasing growth temperature. This behavior was correlated with the emergence of resistive sulfur-rich Sn₂S₃ phase at high temperatures.     

A simple synthesis of SnS nanoflakes at ambient conditions

The present work reports a simple route to prepare tin monosulfide semiconductor nanocrystals at ambient conditions. In the presence of complexant L-tartaric acid, SnCl₂·2H₂O was dissolved in ethylene glycol (EG) solution. After adjusting the solution pH value, sodium sulfide dissolved in EG was added into the solution. The solution changed from colorless into brown immediately and phase-pure SnS, which was confirmed by powder X-ray diffraction (XRD) was produced. The transmission electron microscopic (TEM) investigation shows very thin rectangular flake like SnS crystals of 10∼20 nm in size. PACS 81.05.Hd; 81.07.Bc; 81.16.Be; 81.16.Dn; 81.20.Ka     

On the universal regularities of the lattice dynamics in ferroelectrics

The main regularities revealed for the dynamic response in recent Raman spectroscopic investigations of ferroelectric crystals of the displacive type (LiNbO₃, LiTaO₃) and the order-disorder type (KDP, DKDP) are discussed. The characteristic feature of the dynamic response for all the crystals (KDP, DKDP, LiNbO₃, LiTaO₃) under investigation in the vicinity of the phase transition temperature is an intense central peak that follows from the theoretical predictions for the order-disorder phase transition. The possible factors responsible for the central peak, the character of the behavior of this peak outside the aforementioned temperature range, and the specific features of the behavior of the width and intensity of the central peak over a wide range of temperatures for order-disorder crystals are analyzed.     

Measurement of integral diffraction coefficients of crystals on beamline 4B7 of Beijing Synchrotron Radiation Facility

Integral diffraction coefficients of the crystal are the essential data of a crystal spectrometer which is extensively used to measure quantitative x-ray spectra of high temperature plasmas in kilo-electron-volt region. An experimental method has been developed to measure the integral diffraction coefficients of crystals on beamline 4B7 of Beijing Synchrotron Radiation Facility. The integral diffraction coefficients of several crystals including polyethylene terephthalate (PET), thallium acid phthalate (TlAP) and rubidium acid phthalate (RAP) crystals have been measured in the x-ray energy range 2100--5600 eV and compared with the calculations of the 'Darwin Prins' and the 'Mosaic' models. It is shown that the integral diffraction coefficients of these crystals are between the calculations of the 'Darwin Prins' and the 'Mosaic' models, but more close to the `Darwin Prins' model calculations.     

Atomic 6p-Tl0 centers in ferroelectric Rb2ZnCl4 crystals

Abstract

Several Tl⁰ (6s²6p ¹)-type paramagnetic centers, produced by low temperature X-ray irradiation, were observed and studied by electron spin resonance (ESR) in the orthorhombic ferroelectric phase of thallium doped Rb₂ZnCl₄ crystals. The centers were formed by electron trapping at Tl⁺ ions localized substitutionally at Rb⁺ sites. The number and properties of the observed centers account for the tripling of the unit cell in the ferroelectric phase.     

Reflection spectra of (alkali metal,thallium (I), silver (I)) iridium (IV) hexachlorides

While the effect of rubidium and caesium ions in solid salts of IrCl₆ ^-- is a shift to lower wave-numbers, comparable to that occurring in organic solvents relative to water, the dark blue silver (I) and thallium (I) salts have a new, broad band in the red. Mixed crystals of Cs₂IrCl₆ and Tl₂IrCl₆ are prepared, and the absorption spectra are discussed in terms of a tendency to ‘ferroelectric rattling’ and strong covalent bonding of Ag and Tl. Analogous cases are pointed out in solid salts of other 5d-hexahalides.     

Low-temperature X-ray studies of TlInS2, TlGaS2, and TlGaSe2 single crystals

The results of X-ray diffraction studies of the unit-cell parameters and thermal-expansion coefficients of TlInS₂, TlGaS₂, and TlGaSe₂ crystals in the temperature range 100–300 K are described. It is shown that the unit-cell parameters of all the studied crystals gradually increase with increasing temperature. The temperature dependences of these parameters exhibit anomalies in the form of bends and kinks at temperatures corresponding to phase transitions in the crystals. The thermal-expansion coefficients along the [001] crystallographic direction of the crystals under study are determined. It is found that their values slightly change with increasing temperature.     

Optical properties and radiation effects in layered crystals of (CnH2n+nNH3)2MCl4: n = 1, 2, 3; M = Cd,Cu, Mn

Abstract

A new absorption band has been found at 5.10 eV in (C _n H_{2n + 1}NH₃)₂CdCl₄: n = 1, 2, 3 in addition to the absorption bands of CdCl₂ whose electronic structure resembles the former crystals. The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10eV at room temperature (RT) to 5.48 eV at liquid nitrogen temperature. This large peak shift is attributed to a structural phase transition between these two temperatures. A new type of electron center has been found in these crystals (M = Cd, Mn; n = 1, 2, 3) irradiated with X-rays at 15 K in addition to the Cl₂ ^?. This shows optical absorption bands (IR bands) in the infrared region of 10 ～ 20 kcm ^?1. The IR bands are assigned to an electron center where an electron is trapped at an ammonium site in the neighborhood of a Cl^? vacancy.     

Giant dielectric relaxation in TlGaTe<Subscript>2</Subscript> crystals

The conductivity and temperature-frequency dependences of the permittivity of TlGaTe₂ crystals have been studied. Strong dielectric relaxation has been revealed. It has been shown that the mechanism of dielectric relaxation is associated with hopping of Tl ions over vacancies in the thallium sublattice due to the transition of the system to the superionic state.     

Dielectric, piezoelectric and elastic properties of tetragonal BiScO3-PbTiO3 single crystal with single domain

Modified BiScO₃-PbTiO₃ (BSPT) tetragonal single crystals were grown using high temperature solution method. The dielectric, piezoelectric and elastic properties of single domain BSPT crystals, after poling along [001] crystallographic direction, have been determined experimentally using the resonance method. The results showed that the BSPT tetragonal crystals possess good piezoelectric properties, with electromechanical coupling factor about 88% and piezoelectric coefficient over 400 pC/N at room temperature. BSPT tetragonal crystals have high Curie temperature around 436 °C and high coercive field ∼28 kV/cm, also, the crystal exhibited a very good temperature stability of the properties till 380 °C. For comparison, the material constants of tetragonal Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PZNT) single crystals were measured and listed in this paper.