On the Kinetics of Interface Processes on Silver Halide Crystals

In the present paper the activation energies of the transport of Ag⁺ ions in AgCl and AgBr crystals are calculated with the help of a quantum theoretical equation involving the frequency of the optical phonons of the crystal lattice, the mean coordination number for the diffusing ion, and the vibrational quantum number. Comparison of the calculated activation energies with values available from the literature, which were obtained by measurements of electrical conductivity, dielectric loss, diffusion and mass transfer processes, shows good agreement.     

On the preparation and electrical properties of thallium selenide monocrystals

Thallium Selenide single crystals were prepared by a special design using Bridgmantechnique constructed by the authors. An investigation was made on the influence of temperature on the electrical conductivity and Hall effect in two crystallographic directions. The anisotropic properties were checked, and the anisotropic factor was observed to increase with temperature decrease. The energy gap as well as the ionization energy was calculated. The conductivity throughout the entire temperature range was found to be of p-type. The Hall mobilities derived from these measurements at room temperature were of the order μH_⟂ = 42.66 cm²/vs and μH_∥ = 112.2 cm²/vs.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Electronic Transport Properties of Thallium Sesquiselenide Single Crystals

Electronic transport measurements were made on single crystal samples of Tl₂Se₃. The crystals were prepared by a special design based on Bridgman technique. The influence of temperature on the electrical conductivity, Hall effect, Hall mobility and the carrier concentration was investigated in the temperature range 200–400 K. The energy gap as well as the ionization energy were calculated. The scattering mechanism of the charge carrier was discussed in the same temperature range.     

Transport Properties of TlInSe2 Single Crystals

Single crystals of TlInSe₂ were prepared by a special modified Bridgman technique. The influence of temperature on the electrical conductivity, Hall effect, Hall mobility, and the carrier concentration was investigated in the temperature range 190–625 K. The energy gap of conduction was calculated. The scattering mechanism of the charge carrier was discussed in the same temperature range. Beside this, the thermoelectric power was measured in a temperature range extending from 190 up to 485 K.     

Electrical conduction in ferroelectric lead hydrogen phosphate single crystals

Single crystals of LHP (Lead Hydrogen Phosphate) have been grown using the controlled reaction between lead nitrate and orthophosphoric acid solution by diffusion process in silica gel medium. Transparent crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The d.c. electrical conductivity of both single crystals and pelletized samples of LHP have been studied in the temperature range from 313 to 968 K. It has been observed that: (i) the d.c. conductivity of the crystalline sample is greater than that of thepellet sample, (ii) three distinct electrical conductivity processes have been observed and are interpreted as extrinsic, intrinsic, phase changes, and (iii) the activation energy for the conduction in the crystalline sample is greater than that of the pellet sample. The magnetic susceptibility measurements reveal that the paramagnetic characteristic of these materials and the implications are discussed.     

Preparation and characterization of Ni-incorporated FeS2 single crystals

Nickel-incorporated FeS₂ single crystals with various Ni compositions of Fe_0.99S₂:Ni_0.01, Fe_0.98S₂:Ni_0.02, Fe_0.96S₂:Ni_0.04, and Fe_0.9S₂:Ni_0.1 were grown by chemical vapor transport (CVT) method using ICl₃ as a transport agent. Physical properties of the Ni-incorporated FeS₂ single crystals were characterized using X-ray diffraction, Raman spectroscopy, electrical conductivity, and photoconductivity (PC) measurements. By means of the analyses of the X-ray diffraction patterns, the whole series of Ni-doped FeS₂ single crystals were determined to be single-phase and isostructural. Raman spectroscopy of the Ni-doped FeS₂ crystals was carried out at room temperature. Raman resonant peaks of the Ni-doped FeS₂ crystals demonstrate an energy red-shift behavior with respect to the increase of the dopant densities. Conductivity measurements show the resistivity of the Ni-doped FeS₂ decreased as the doping concentration of Ni is increased. Nickel is an n-type dopant, which behaves like a donor level existed near the conduction band edge of the synthetic FeS₂. On the other hand, dopant effect of nickel on the synthetic FeS₂ also destroys the photoconductive sensitivity in the photoconductivity measurements.     

Electrical conductivity of 2,4-dinitrosoresorcinol and its complexes

Electrical conductivity measurements of 2,4-dinitrosoresorcinol (DNR) and its complexes were measured in the temperature range 20–115°C to give faint semiconducting behaviour for these systems. The conductivity values of the bis Co, Ni, Cu and Zn systems indicated that the metal ion forms a bridge between the two ligands facilitating the transfer of current carriers with some degree of delocalization in the excited state. As the iron content in the complexes increased, a gradual increase of electrical conductivity occurred, that might be due to lattice imperfections.     

New technique for crystal growth and Phase Transition in TlInS2 Crystals

New technique for crystal growth was designed in the present work. The electrical conductivity and Hall effect of the TInS₂ single crystals, grown by this technique, were measured in the temperature range 150–500 K. From the measurements, the conductivity type, the energy gap, ionization energy of the impurity level, Hall mobility and carrier concentration were determined. Also the measurements revealed a presence of phase transition in the crystal at 189 and 220 K.     

Transport property measurements in tungsten sulphoselenide single crystals grown by a CVT technique

The transport properties of ternary mixed WS_xSe_2‐x single crystals have been studied by measuring the thermo power, electrical conductivities and Hall parameters in a small temperature range 303‐423 K. The electrical conductivity was highest for selenium rich WSe₂ and lowest for sulphur rich WS₂ crystals. All the crystals showed semiconducting behaviour from the temperature dependence of ‘ρ’, ‘R_H’ and ‘S’. The Hall coefficients showed that the samples are p‐type conducting. The temperature dependence of resistivity, Hall coefficients, carrier concentration showed that all of them are thermally activated. The values of activation energies, pre‐exponential factors and the scattering parameters have been determined. The dominant scattering mechanism for the charge carriers has been explained. The relation between the TEP and the concentration of charge carriers and electrical conductivity was studied. The effective masses of holes and the effective density of states have been determined. These parameters show an increase with increase in sulphur content. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical simulation of a new SiC growth system by the dual-directional sublimation method

A new SiC growth system using the dual-directional sublimation method was investigated in this study. Induction heating and thermal conditions were computed and analyzed by using a global simulation model, and then the values of growth rate and shear stress in a growing crystal were calculated and compared with those in a conventional system. The results showed that the growth rate of SiC single crystals can be increased by twofold by using the dual-directional sublimation method with little increase in electrical power consumption and that thermal stresses can be reduced due to no constraint of the crucible lid and low temperature gradient in crystals.     

Ionic conductivity studies in KCl–NaCl mixed crystals

Single crystals of KCl and a few compositions of KCl-NaCl mixed crystals were grown from melt by Kyropoulos technique. Ionic conductivity measurements have been carried in these crystals in the temperature range 100 to 400 °C. The activation energy for the migration of charge carriers have been calculated from the conductivity-temperature plots of these crystals and the results obtained were discussed.     

Crystallization kinetics of 1Na2O · 2CaO · 3SiO2 · glass monitored by electrical conductivity measurements

We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glass with composition close to the stoichiometric 1Na₂O · 2CaO · 3SiO₂. The nucleation and subsequent growth of sodium-rich crystals in this glass decreases the sodium content in the glassy matrix, drastically hindering further nucleation and growth. Compositional changes of the crystals and glassy matrix at different stages of the crystallization process were determined by EDS. These compositional variations were also monitored by electrical conductivity measurements, carried out by impedance spectroscopy, in glassy, partially, and fully crystallized samples. The electrical conductivity of both crystalline and glassy phases decreases with the increase of the crystallized volume fraction. Starting at a crystallized volume fraction of about 0.5, the crystalline phase dominates the electrical conductivity of the sample. This behavior was corroborated by an analysis of the activation energy for conduction. We show that electrical conductivity is highly sensitive and can indicate compositional shifts, changes in the spatial distribution of mobile ions in the glassy matrix. Conductivity measurements are thus a powerful tool for the investigation of complex heterogeneous systems, such as partially crystallized glasses and glass-ceramics.     

Studies on electrical and the dielectric properties in MS structures

In this study, we investigated frequency dependent electrical and dielectric properties of metal-semiconductor (MS) structures using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics in the frequency range 100 kHz-10 MHz in the room temperature. The dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ) and ac electrical conductivity (σ_ac) were calculated from the C-V and G/ω-V measurements and plotted as a function of frequency. In general, ε′, ε″ and tan δ values decreased with increasing the frequency, while σ_ac increased with increasing frequency. Furthermore, the voltage and frequency dependence of series resistance were calculated from the C-V and G/ω-V measurements and plotted as functions of voltage and frequency. The distribution profile of R_S-V gives a peak in the depletion region at low frequencies and disappears with increasing frequencies. Also, series resistance values decreased with increasing frequency. The experimental results show that both frequency dependent electrical and dielectric parameters were strongly frequency and voltage dependent.     

Effect of Doping and Irradiation on Optical Parameters of Triglycine Sulphate Single Crystals

Crystals of triglycine sulphate (TGS) doped with orthonitroaniline (ONA) irradiated with different doses of gamma-radiation were used to investigate gamma-radiation effect on electrical and optical parameters. The absorption coefficient and the reflectance were measured and hence the extinction coefficient, the optical refractive index and the dielectric constants (e_r′, e_r″) of unirradiated and irradiated TGS crystals were calculated. Values of the allowed indirect optical energy gap E_g^opt. of TGS doped with ONA were calculated as a function of gamma-dose. Value of E_g^opt. decreases from 4.72 eV to 4.25 eV with increasing gamma-doses from 0 up to 3 Mrad. The values of the static dielectric constant e_r(0) and the effective electrical conductivity sigma₀ at room temperature and their dependence on gamma-dose were also calculated.     

Electrical conductivity and dielectric properties of potassium sulfamate single crystals

Single crystals of potassium sulfamate are grown by the method of slow evaporation at constant temperature. AC electrical conductivity of potassium sulfamate is measured in the temperature range 300–430 K and in the frequency region between 100 Hz and 3 MHz along the a, b and c‐axes. Complex impedance spectroscopy is used to investigate the frequency response of the electrical properties of the potassium sulfamate single crystal. Temperature variation of AC conductivity and dielectric measurements show a slope change around 345 K for both heating and cooling run and this anomaly is attributed as phase transition, which is well supported by the DSC measurements. Value of loss tangent in the temperature region 330–400 K is found to be very low. Activation energies for the conduction process are calculated along the a, b and c‐axes. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Orientation dependence of electrical and optical properties of ZnSiP2 crystals grown from melt

Undoped and Ga-doped ZnSiP₂ crystals grown by spontaneous crystallization from nonstoichiometric melt show a pronounced dependence of electrical properties (conductivity, carrier concentration) and cathodoluminescence on the orientation of various crystal faces. Breakdown voltage measurements and Hall measurements yielded that the (112)B face is always low-resistivity n-type and the (112)A face is always semi-insulating. The spectral position of the broad luminescence band observed at 80 K differs in a characteristical manner for the various crystal faces. The luminescence behaviour correlates partly with the electrical properties. The results are explained by an orientation dependence of the impurity incorporation which is reflected also in the bulk properties of the crystals.     

Electrical conductivity of sulfamic acid single crystals

Single crystals of sulfamic acid have been grown by the method of slow evaporation at constant temperature. DC electrical conductivity was measured in the temperature range 300 ‐ 440 K along a, b and c‐axes. Conductivity measurements show slope change near 330 K and 410 K. The slope change observed around 330 K may be attributed as due to a phase transition which has been well supported by the DSC and DTA measurements. Slope change observed around 410 K is attributed as the onset of the thermal decomcoposition as evidenced by TGA curve. TGA studies show the crystal is very stable up to 440 K. Activation energies for the conduction process are calculated for all measured crystallographic directions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ionic Conductivity of KBr?KI Mixed Crystals

Ionic conductivity studies have been made on the mixed KBr KI single crystals in the temperature region 150°–650 °C. The log σ versus 1/T plots indicate four different regions. The activation energies associated with different regions have been calculated and its variation with the composition of the mixed crystals is reported. The results obtained are correlated with the theoretical values calculated using Lidiard theory. An attempt is made to understand the results.     

Study of the temperature dependence of the electrical conductivity in strontium-barium niobate crystals with different dopants

The electrical characteristics of single crystals of strontium-barium niobate solid solutions have been studied. The temperature dependences of the electrical conductivity were obtained for different SBN compositions, nominally pure SBN:61 and SBN:75 and SBN doped with rare earth and transition-metal impurities. The influence of the chemical composition of a solid solution, thermal treatment conditions, dopant concentration, and electrode type on the specific features of the electrical conductivity of single crystals in the temperature range 20–450°C is shown.