Electric Characterization of Indium Sesquiselenide Single Crystals

Conductivity, Hall-effect measurements were performed on δ-phase In₂Se₃ single crystals, grown by the Bridgman method over the temperature range 150–428 K, in the directions perpendicular and parallel to the c-axis. The anisotropy of the electrical conductivity and of the Hall coefficient of n-type In₂Se₃ had been investigated. The values of the Hall coefficient and electrical conductivity at room temperature spreads from an order of R_H11 = 1.36 × 10⁴ cm³/coul, σ₁₁ = 4.138 × 10⁻³ Ω⁻¹ cm⁻¹ and R_H = 66.55 × 10⁴ cm³/coul, σ = 0.799 × 10⁻³ Ω⁻¹ cm⁻¹ for parallel and perpendicular to c-axis, respectively. The temperature dependence of Hall mobility and carrier concentration are also studied.     

Single Crystal Growth and Electrical Properties of Gallium Monotelluride

Single crystals of GaTe were prepared in our laboratory by a special modified Bridgman technique method. Measurements of the electrical conductivity and Hall effect between 210 and 450 K were carried out on GaTe samples in two crystallographic directions. The Hall coefficient is positive and varies with the crystallographic direction. A unique mobility behaviour and strong anistropy in the carrier mobility were observed. The Hall mobilities parallel and perpendicular to the C-axis, at room temperature, were 12 cm/V · s and 25.12 cm²/V ·s, respectively. The free carrier concentration lies between 10¹³ − 10¹⁴ cm⁻³ at room temperature.     

Growth condition related orientation transition for YBa2Cu3O7−δ films on NdGaO3 substrate

For comprehensive understanding, the crystallographic out-of-plane axis transition for YBa₂Cu₃O_7?δ (YBCO or Y123) films grown on (110) NdGaO₃ (NGO) substrate, using liquid phase epitaxy (LPE), was systematically investigated via changing flux composition, processing temperature and oxygen partial pressure. It is found that LPE films could grow, remarkably, in a wide temperature range between 24 K above and 25 K below the peritectic temperature (T_p). The unpredicted c-oriented films formed at the temperatures above T_p, is deduced to be attributed to the etch-back behavior, i.e., Nd partially dissolved from the NGO substrate into solution, which leads to a locally high supersaturation for facilitating film growth. Even more distinctively, decreasing from the high temperature in this wide range, the YBCO films characteristically experienced the orientation transitions, the double transition of the c-axis oriented→a/c-axis mixed→c-axis oriented in air, and a single evolution of the c-axis→a-axis in the pure oxygen atmosphere. By combining supersaturation with the NGO etch-back, and solute diffusion, the transition origin of the film orientation in various temperature regions was clarified.     

Thermal expansion in CuAlTe2 compound

The lattice parameters a and c as well as the axial thermal expansion coefficients α ⟂ and α ∥ in the CuAlTe₂ chalcopyrite-type compound are determined as a function of temperature in the range from 80 to 650 K by a X-ray diffractometry technique. The data obtained are used to evaluate the axial ratio c/a, the tetragonal distortion δ = 2 — c/a, the interatomic distances for Cu Te and Al Te bonds and their temperature coefficients. It is found that the thermal expansion behaviour of CuAlTe₂ is similar to that of other CuB^IIIC^VI₂ compounds in having a relatively small expansivity along the c-axis and a large one in the perpendicular direction. When comparing the results for a series of the CuB^IIIC^VI₂ compounds (B Al, Ga, In; C S, Se, Te) it is shown that the correlations between the thermal expansion coefficients α ⟂, α ∥, α_m, dδ/dT and the tetragonal distortion δ, as well as the molar mass of the compound take place.     

Temperature dependence of electrical conductivity and hall effect of Ga2Se3 single crystal

Electrical conductivity (σ) and Hall coefficient (R_H) of single crystal grown from the melt have been investigated over the temperature range from 398 K to 673 K. Our investigation showed that our samples are p-type conducting. The dependence of Hall mobility an charge carrier concentration on temperature were presented graphically. The forbidden energy gap was calculated and found to be 1.79 eV. The ionization energy of impurity level equals 0.32 eV approximately. At 398 K the mobility equals to 8670 cm² V⁻¹ s⁻¹ and could described by the law μ = aTⁿ (n = 1.6) in the low temperature range. In the high temperature range, adopting the law μ = bT^–m (as m = 1.67), the mobility decreases. This result indicates that in the low temperature range the dominant effect is scattering by ionized impurity atoms, whereas in the high temperature range the major role is played by electron scattering on lattice vibrations (phonons). At 398 K the concentration of free carriers showed a value of about 1.98 × 10⁷ cm⁻³.     

Crystal growth of InN by MOCVD with electric field along the c-axis

We report on physical properties of InN grown by metalorganic chemical vapor deposition (MOCVD) with electric field applied along the c-axis. The electric field is applied continuously from the growth of the low temperature InN buffer layer to the procedure of cooling down to room temperature. As a result, the crystal morphology degrades, c-lattice constant elongates by 0.12% at ±1 kV/cm, Hall mobility decreases, and the phonon vibration along the c-axis broadens, which suggests that the physical properties of InN can be controlled by the electric field applied along the c-axis during the crystal growth.     

Structural and Electrical Characterization of Ag3Ga5Te9 and Ag3In5Se9 Crystals

X-ray powder diffraction studies revealed that Ag₃Ga₅Te₉ and Ag₃In₅Se₉ crystallize in orthorhombic and tetragonal systems, respectively. The temperature dependent conductivity and Hall effect measurements have been carried out between 65—480 K. Ag₃Ga₅Te₉ exhibits p-type conduction with a room temperature conductivity of 4.3 × 10^—4 (Ω · cm)^—1 and mobility less than 1 cm²/V · s. Ag₃In₅Se₉ was identified to be n-type with room temperature conductivity 7.2 × 10^—5 (Ω · cm)^—1 and mobility 20 cm²/V · s. From temperature dependence of the conductivity three different impurity ionization energies were obtained for both compounds. The anomalous behavior observed in the temperature dependence of mobility was attributed to the different features of the microstructure.     

Thermal Expansion of Thiourea in the Range of Phase Transition

By means of a quartz dilatometer three principal expansion coefficients have been determined in the temperature range 100–273°K, and their anisotropy within (100) plane. The appearance of singular points, corresponding to phase transformations, depends on direction of measurements but most drastic changes are observed along the crystallographic c-axis, in agreement with the direction of the weakest intermolecular interactions. The calculated pressure necessary to shift the phase equilibrium I/II to room temperature is in good agreement with the value observed in a direct experiment.¹¹     

Thermal expansion in the AgGa(S1−xSex)2 solid solutions from X-ray diffraction data

The lattice parameters a and c as well as the axial thermal expansion coefficients in the AgGa(S_1-xSe_x)₂ solid solutions with chalcopyrite-type structure were determined as a function of temperature in the range from 80 to 700 K and composition x using an X-ray powder diffractometry technique. It is found that the thermal expansion coefficients were anisotropic and for all the solid solutions the thermal expansion coefficients along the tetragonal c-axis were negative whereas those along the a-axis and the volume coefficients were positive. The directions in which the crystal thickness does not change as temperature varies, were found. The composition dependences of these coefficients were non-linear.     

Crystal Data,Electrical Resisitivity and Mobility in Cu3In5Se9 and Cu3In5Te9 Single Crystals

X-ray powder diffraction data were obtained for Cu₃In₅Se₉ and Cu₃Te₉, which were found to crystallize in orthorhombic and tetragonal systems, respectively. The electrical resistivities and Hall mobilities of these compounds were investigated in the temperature range 35–475 K. Cu₃In₅Se₉, was identified to be n-type with a room temperature resistivity of 3 × 10³ Ω·cm which decreases with increasing temperature. For T < 65 K impurity activation energy of 0.03 eV and for T > 350 K onset of intrinsic conduction yielding a band gap energy of 0.99eV were detected. The neutral impurity scattering was found to dominate at low temperatures, while in the high temperature region thermally activated mobility was observed. Cu₃In₅Te₉ exhibits p-type conduction with a room temperature resistivity of 8.5 × 10⁻³ Ω·cm decreasing sharply above 400 K and yielding an impurity ionization energy of 0.13 eV. The temperature dependence of mobility indicates the presence of lattice and ionized impuritiy scattering mechanisms above and below 160 K, respectively.     

Synthesis of Dysprosium Oxychloride (DyOCl)

Dysprosium oxychloride, DyOCl, was synthesized using a simple hydrolysis method with DyCl₃·6H₂O. X-ray powder diffraction (XRD) data was used to determine the crystal structure. The DyOCl compound is isostructural to the matlockite (PbFCl) crystal structure and crystallizes in the tetragonal P4/nmm (#129) space group. The crystal structure contains the alternating cationic layers of (DyO)_n and anionic layers of nCl^? along the c-axis. The structural data including unit cell, volume, and density of DyOCl were compared to other rare-earth oxychloride data from the Inorganic Crystal Structure Database (ICSD) and our previous study on TbOCl. Fourier-transform infrared spectroscopy was performed on DyOCl and peaks observed at 543 and 744 cm^?1 were attributed to Dy–O and Dy–Cl. Scanning electron microscopy analysis showed irregularly shaped crystals. Hot-stage XRD, thermogravimetry, as well as differential scanning calorimetry coupled to a gas chromatograph and a mass spectrometer (evolved gas analysis) were performed on DyCl₃·6H₂O to understand the phase transformation to DyOCl (and Dy₂O₃) as a function of temperature and time at temperature.

Graphic Abstract

DyOCl compound with the tetragonal P4/nmm space group is composed of the alternating layers of (DyO)_n and nCl^? along the c-axis.

     

Anisotropy of the ionic conductivity of CsCu2Cl3 single crystals

The conductivity of CsCu₂Cl₃ single crystals (orthorhombic system, sp. gr. Cmcm) has been investigated for different electric-field directions, perpendicular to the crystallographic c axis and along it, in the temperature range 390–530 K. The increase in conductivity with temperature is due to the ion-carrier transport with activation energies E _a = 0.65 and 0.80 eV for the directions perpendicular to and along the crystallographic axis, respectively. The anisotropy of the crystal ionic conductivity is found to be σ_⊥c /σ_∥c ≈ 40 at 435 K. The thermally activated contribution to the conductivity in the CsCu₂Cl₃ structure is determined by the transport of Cu⁺ ions.     

Concentration dependence of the critical resolved shear stress of Cd-Zn single crystals in the temperature interval 1.5 K—50 K

Cd—Zn single crystals were deformed in creep at temperatures between 1.5 K and 50 K. The from the creep experiments established critical resolved shear stress (CRSS) increases with cⁿ where c is the atomic concentration of zinc as solute. The exponent n was found to be close to 2/3, i.e. the concentration dependence of the CRSS can be explained according to the theory of LABUSCH .     

On a Hypothesis on the Molecule Vacancies in PbTe

The temperature dependence of the current carriers mobility in SnTe(I) and PbTe (I) synthesized in presence of SnI₂ or PbI₂ respectively was studied. An experimental formula was established, showing that current carriers scattering in SnTe(I) is due to vacancies at constant Hall coefficient. For PbTe (I) crystallized from tellurium solution by traveling heater method the mobility is high (between 2.10⁴ and 4.10⁴ cm²/Vs) and the Hall coefficient is constant within the interval 77 K–450 K. Only within 77 K–160 K interval the current carriers scattering is due to vacancies. A hypothesis is proposed based on the presence of molecular vacancies (V_pbTe). These vacancies do not change electron gas concentration but do change the carriers mobility. Specimens with a negligibly low lead atoms vacancies Concentration were investigated. An empirical expression is established which shows that their mobility depends on molecular vacancies concentration and explains observed weak temperature influence upon carriers mobility. These results are obtained only from Hall coefficient and electric conductivity measurements within the 77 K–160 K temperature interval.     

Carrier Scattering Mechanisms in GaS0.5Se0.5 Layered Crystals

Systematic dark electrical resistivity and Hall mobility measurements have been carried out in the temperature range 150‐400 K on n‐type GaS_0.5Se_0.5 layered crystals. The analysis of temperature dependent electrical resistivity and carrier concentration reveals the extrinsic type of conduction with a donor impurity level located at 0.44 eV, donor and acceptor concentrations of 3.4 ×10¹⁷ and 4.1×10¹⁶ cm^‐3, respectively, and an electron effective mass of 0.41 m₀. The Hall mobility is limited by the electron‐phonon short‐range interactions scattering at high temperatures combined with the ionized impurity scattering at low temperatures. The electron‐phonon short‐range interactions scattering mobility analysis reveals an electron‐phonon coupling constant of 0.25 and conduction band deformation potential of 5.57 eV/Å.     

On crystal chemistry and morphology of extended organic molecules

The present paper is concerned with the morphology and crystal structure of extended organic compounds in the space group P 2₁/c. In the structures with molecules in general position (Z = 4) the longitudinal axis of all molecules run parallel to a (h0l)-plane. The molecule arrangements are based on four different structure types. The planes through the molecule axis contain a) 2₁-axis and symmetry centres (l = 2n), b) 2₁-axis or symmetry centres (l = 2n + 1) and c) respectively d) no symmetry element (l = 2n resp. 2n + 1). In the last two cases the net plane distances are to be halved. As in P 2₁/c the a-und c-axis are not set, one can confine oneself to the examination of the net planes (1 02), (2 02), (2 04), and (4 04). In the cases of a) and b), only certain morphological lattices appear, which distinguish themselves through additional translations in three-dimensional space resp. in the projections. In the cases of c) and d) there are also found morphological lattices which generate additional “morphological extinctions” (consequently possessing a higher symmetry than the generating space group), but which contain no translationally higher symmetry. (h0l)-faces, to which the molecule axis run parallel, appear with preference on crystals. As a rule the first two and the last two cases can be differentiated on account of the position of the (h0l)-faces in the Donnay-Harker series. Some examples will show that the morphological lattice can be preserved through Fourier transformation of crystal morphology.     

Effect of low temperature thermocycling on microhardness anisotropy of commercially pure beryllium

Commerically pure beryllium polycrystals prepared by hot uniaxial crucible extrusion have been used for statistical investigation of the microhardness distribution on various faces distinguished by the orientation with respect to the extrusion axis. The microhardness anisotropy coefficient K (the relative difference of the statistical average values of microhardness for faces perpendicular and parallel to the extrusion axis) of the tested material was high. Low temperature thermocycling between 300 and 77 K essentially reduced K, which is thought to be a result of structural state changes and internal stress redistribution in the material induced by thermoeleastic stresses due to thermocycling. The result of the experiment is in qualitative agreement with data on the beryllium defect structure and fracture character found by transmission and scanning electron microscopy.     

Annealing effect on electrical and photoconductive properties of Si implanted GaSe single crystal

GaSe single crystals grown by Bridgman method have been doped by ion implantation technique. The samples were bombarded in the direction parallel to c‐axis by Si ion beam of about 100 keV to doses of 1 × 10¹⁶ ions/cm² at room temperature. The effects of Si implantation with annealing at 500 and 600 °C on the electrical properties have been studied by measuring the temperature dependent conductivity and photoconductivity under different illumination intensities in the temperature range of 100–320 K. It is observed that Si implantation increases the room temperature conductivity 10⁻⁷ to 10⁻³ (Ω‐cm)⁻¹ depending on the post annealing temperature. The analysis of temperature dependent conductivity shows that at high temperature region above 200 K, the transport mechanism is dominated by thermal excitation in the doped and undoped GaSe samples. At lower temperatures, the conduction of carriers is dominated by variable range hopping mechanism in the implanted samples. Annealing of the samples at and above 600 °C weakens the temperature dependence of the conductivity and photoconductivity. This indicates that annealing of the implanted samples activates Si‐atoms and increases structural deformations and stacking faults. The same behavior was observed from photoconductivity measurements. Hence, photocurrent‐illumination intensity dependence in the implanted samples obeys the power low I_pc ∝ Φⁿ with n between 1 and 2 which is an indication of continuous distribution of localized states in the band gap. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correlation between growth orientation and growth temperature for bismuth tri‐iodide films

This paper reports the growth of bismuth tri‐iodide thick films intended for direct and digital X‐ray imaging. Films were grown by the vertical physical vapor deposition method, onto glass substrates 2″x 2″ in size, with gold previously deposited as rear electrode. The film thickness was up to 33 μm (±5 %). Optical microscopy and SEM were performed on the films and grain size resulted to be up to 40 μm. A strong correlation was found between the microcrystals growth orientation and the growth temperature. At low temperatures, microcrystals grow with their c axis parallel to the substrate, whereas at higher temperatures, they grow with their c axis perpendicular to the substrate. The higher the growth temperature, the lower the dark current of the film, and the higher the resistivity, which was from 10¹³ to 10¹⁵ Ωcm. A sensitivity to X‐rays of 6.9 nC/R.cm² was measured irradiating the films with X‐rays from a mamographer. Film properties were correlated with the growth temperature, with previous results for bismuth tri‐iodide films and monocrystals and with data for films of alternative materials such as lead and mercuric iodide. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Liquid phase epitaxial growth of undoped gallium arsenide from bismuth and gallium melts

Electrical properties of undoped GaAs layers grown from Ga and Bi melts under identical conditions are compared as a function of growth temperature and pregrowth baking time. Identification of residual shallow donors and acceptors is performed by means of laser photoelectrical magnetic spectroscopy and low temperature photoluminescence. It is shown that a change of solvent metal results in complete alteration of major background impurities in grown epilayers due, mainly, to changes of distribution coefficients of these impurities. High purity, low compensation n-GaAs layers can be grown from Bi melt (epilayers with the Hall mobility of electrons μ77K ≈ 150000 cm²/V · sat n = 2.5 · 10¹⁴ cm⁻³ has been grown).