Crystal growth and structural analysis of zirconium sulphoselenide single crystals

A series of zirconium sulphoselenide (ZrS _x Se_3−x , where x = 0, 0·5, 1, 1·5, 2, 2·5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrS _x Se_3−x single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are n-type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrS _x Se_3−x series. The electrical resistivity parallel to c-axis as well as perpendicular to c-axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.     

Transport properties of MoSe x Te2−x (0 ≤x ≤ 2) single crystals

The layer type MoSe _x Te_2−x (0 ≤x ≤ 2) have been grown in single crystalline form by chemical vapour transport technique using bromine as the transporting agent. The electrical resistivity and Hall mobility perpendicular to thec-axis of the crystals were measured at room temperature. The variation of the Seeback coefficient with temperature was also investigated.     

Growth and transport property measurements of rhenium doped tungsten diselenide single crystal

Single crystals of rhenium doped tungsten diselenide i.e. Re_xW_1−xSe₂ (x = 0, 0.0005, 0.001, 0.05, 0.1) are grown by vapour phase technique. The stoichiometry of grown single crystals is confirmed by energy dispersive analysis of X-rays. X-ray powder diffractograms obtained of these compounds were used for lattice parameter determination based on hexagonal system similar to that of host WSe₂.The crystallite size for each sample for different reflection is calculated using Scherrer's formula. Surface morphology as observed under optical microscope reflects that screw dislocation mechanism is responsible for growth of crystals. Electrical properties viz. Hall effect at room temperature, resistivity measurements at low temperature, and high pressure resistivity measurements indicates the semiconducting behaviour of Re_xW_1−xSe₂ (x = 0, 0.0005, 0.001, 0.05, 0.1) single crystals. Thermoelectric power measurements shows p-type nature of host WSe₂ whereas n-type nature of rhenium doped WSe₂ which matches with the results of Hall effect.     

Growth and characterization of Hg1-xCdxTe epitaxial films by isothermal vapour phase epitaxy (ISOVPE)

Growth of Hg_1-xCd_xTe epitaxial films by a new technique called asymmetric vapour phase epitaxy (ASVPE) has been carried out on CdTe and CZT substrates. The critical problems faced in normal vapour phase epitaxy technique like poor surface morphology, composition gradient and dislocation multiplication have been successfully solved. The epitaxial films have been electrically characterized by using the Hall effect and capacitance-voltage (C-V) measurements.     

Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

Single crystals of the lamellar compound, ZrSe₃, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe₃ were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe₃ single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.     

Effect of oxygen content on the electrical properties of YBa2Cu3O7−x single crystals

The effect of oxygen content in the single crystals of high-temperature superconductor YBa₂Cu₃O_7−x on the electrical resistivity, the Hall effect in the plane perpendicular to thec axis and the energy gap Δ, measured with tunnelling electron microscope, has been studied. The distribution of the gap along the surface of the crystal was also studied. The results of the study on the relationship between the magnitude of the energy gap Δ and the superconducting transition temperatureT _c of single crystals with various oxygen contents are approximated by the linear dependence 2Δ_av=4·4kT _c .     

Study of electrical properties of CIGS thin films prepared by multistage processes

In this work, the dispersion mechanisms affecting the electric transport in CuIn_1−xGa_xSe₂ (CIGS) thin films grown by a chemical reaction of the precursor species, which are evaporated sequentially in two and three-stage processes are analyzed. It was found, through conductivity and Hall coefficient measurements carried out as functions of temperature, that the electrical conductivity of the CuIn_1−xGa_xSe₂ films is affected by the transport of free carriers in extended states of the conduction band as well as for variable range hopping transport mechanisms, each one predominating in a different temperature range.     

Preparation and some physical properties of Bi2−xInxSe3 single crystals

Bi_2–xIn _x Se₃ (x=0.00 to 0.66) single crystals were prepared using a modified Bridgmann method. Their homogeneity was studied by determining the indium content and the variations of Seebeck coefficient in the directions perpendicular and parallel to the crystal axis. X-ray structure analysis revealed that the volume of the unit cell of Bi_2–x In_xSe₃ crystal lattice decreases with increasing value of x. Measurements of the electrical conductivity, Hall constant and Seebeck coefficient showed that incorporation of the indium atoms into the Bi₂Se₃ crystal lattice results in an increase of free electron concentration for low indium content, whereas the free electron concentration is suppressed in the range of the high indium content. This effect is explained qualitatively on the basis of our ideas on the nature of point defects in Bi_2–x In_xSe₃ crystals.     

In-plane anisotropic electrical and optical properties of gold-doped rhenium disulphide

Au-doped ReS₂ layer crystals were grown by chemical vapour method with iodine as the transport agent. Room temperature Hall effect measurement showed p-type semiconducting character for the doped sample. The electrical conductivities parallel and perpendicular to the crystal b-axis were investigated. The near band-edge temperature-dependent in-plane anisotropic optical properties were studied by the polarization-dependent photoconductivity measurements, with the incident light beam parallel and perpendicular to the crystal b-axis, in the temperature range from 20 to 300 K. The influence of Au in the measured conductivity anisotropy and photoconductivity spectra of doped ReS₂ were analysed and discussed.     

Study of electrical properties of glassy Se100- xTexalloys

Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se_100- x _Te x(x = 10, 20 and 30) over different range of temperatures and frequencies. An agreement between experimental and theoretical results suggests that the a.c. conductivity behaviour of selenium-tellurium system (Se_100- xTex)can be successfully explained by correlated barrier hopping (CBH) model. The density of defect states has been determined using this model for all the glassy alloys. The results show that bipolaron hopping dominates over single-polaron hopping in this glassy system. This is explained in terms of lower values of the maximum barrier height for single-polaron hopping. The values of density of charged defect states increase with increase in Te concentration. This is in agreement with our previous results obtained from SCLC measurements.     

Thermo-chemical properties and electrical resistivity of Zr-based arsenide chalcogenides

Ternary phases in the systems Zr-As-Se and Zr-As-Te were studied using single crystals of ZrAs_1.40(1)Se_0.50(1) and ZrAs_1.60(2)Te_0.40(1) (PbFCl-type of structure, space group P4/nmm) as well as ZrAs_0.70(1)Se_1.30(1) and ZrAs_0.75(1)Te_1.25(1) (NbPS-type of structure, space group Immm). The characterization covers chemical compositions, crystal structures, homogeneity ranges and electrical resistivities. At 1223 K, the Te-containing phases can be described with the general formula ZrAs_xTe_2−x, with 1.53(1)?x?1.65(1) (As-rich) and 0.58(1)?x?0.75(1) (Te-rich). Both phases are located directly on the tie-line between ZrAs₂ and ZrTe₂, with no indication for any deviation. Similar is true for the Se-rich phase ZrAs_xSe_2−x with 0.70(1)?x?0.75(1). However, the compositional range of the respective As-rich phase ZrAs_x−ySe_2−x (0.03(1)?y?0.10(1); 1.42(1)?x?1.70(1)) is not located on the tie-line ZrAs₂-ZrSe₂, and exhibits a triangular region of existence with intrinsic deviation of the composition towards lower non-metal contents. Except for ZrAs_0.75Se_1.25, from the homogeneity range of the Se-rich phase, all compounds under investigation show metallic characteristics of electrical resistivity at temperatures >20 K. Related uranium and thorium arsenide selenides display a typical magnetic field-independent rise of the resistivity towards lower temperatures, which has been explained by a non-magnetic Kondo effect. However, a similar observation has been made for ZrAs_1.40Se_0.50, which, among the Zr-based arsenide chalcogenides, is the only system with a large concentration of intrinsic defects in the anionic substructure.     

Magnetic ordering in Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se crystals grown by solid-state recrystallization

Cr _x Hg_{1 − x} crystals grown by solid-state recrystallization have been characterized by electron paramagnetic resonance spectroscopy, transport measurements, and X-ray microanalysis. The results demonstrate that the crystals contain rectangular HgCr₂Se₄ inclusions elongated along one of their axes and irregularly shaped Cr _x Hg_{1 − x} and CrHg inclusions. In the range 77–400 K, the electrical properties of samples cut from different parts of the crystals are typical of semiconductors with a strongly degenerate electron gas.     

Synthesis and properties of Bi1.6Pb2-xSr2-xCa2Cu3Oy

Bi_1.6Pb_0.4Sr_2-xCa₂Cu₃O_y (x = 0, 0.2, 0.4) high-T_c materials were prepared from oxide-carbonate mixtures and presynthesized mixed oxides. The 2223 superconducting phase was found to be formed most rapidly in thex = 0.4 sample if the Pb-and Ca-containing starting reagents were separated in the initial stage of synthesis. The highest superconducting transition temperature, T_c (R = 0) = 104.3 K, was attained in the stoichiometric 2223 material. The materials were characterized by electrical resistivity, magnetic susceptibility, and Hall effect measurements. The Hall data were used to evaluate carrier concentration and mobility. The 77-K resistivity of the materials was measured as a function of magnetic field.     

Transport Properties of Bi_2S_3 Single Crystals

Bi2S3 single crystals were grown by using a modification of Bridgman method. Measurements of the electrical conductivity, Hall effect and thermoelectric power （TEP） were preformed in two crystallographic directions （parallel and perpendicular to the c-axis）. The measurements showed that the electrical conductivity, Hall mobility, and Seebeck coefficient have anisotropic nature. From these measurements some physical parameters were estimated and the crystals showed n-type of conduction mechanism. Also, values of the energy gap were found to be different in the two directions.     

Phase transformation of <Emphasis Type="Italic">p</Emphasis>-Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GeAs<Subscript>2</Subscript> single crystals at 5.5 GPa

The electrical resistivity and Hall coefficient of oriented single-crystal p-Cd_{1 − x} Mn _x GeAs₂ samples have been measured at high pressures. The results indicate that the crystals undergo a reversible structural transformation at 5.5 GPa, which is independent on the sample orientation.     

Cadmium substituted high permeability lithium ferrite

Polycrystalline Li_0.5-x/2Cd_xFe_2.5-x/22O₄ ferrites wherex = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared by a double sintering ceramic technique and characterized by X-ray diffraction and scanning electron microscopy (SEM). The lattice parameter is found to increase monotonically with the cadmium content. It is explained in terms of the sizes of component ions. The grain size of the samples increases up tox = 0.3 and then it decreases for higher values ofx. A similar trend is observed in the variation of Ms with Cd²⁺ content. The initial permeability (μ_i) is however found to increase continuously withx. The increase in μ_i is attributed to decrease of anisotropy constant K₁ and higher grain size of the samples.     

Copper-related deep acceptor in heat-treated Ge1-xSix single crystals

Hall measurements demonstrate that Cu-doped Ge_1-xSi_x (0 ≤x ≤ 0.15) single crystals quenched after heat treatment at 700–720°C contain a new deep acceptor. The ionization energy of this acceptor is linear in silicon content, E_DA (x) = 0.08 + 0.63x eV. Annealing the Ge_1-xSi_x crystals at 260–270°C leads to the disappearance of the deep acceptors and an equivalent increase in the concentration of shallow acceptors related to substitutional copper. The deep acceptor consists most likely of a substitutional copper atom and a mobile defect, presumably a vacancy or a copper, carbon, or oxygen interstitial.     

Electrical and optical properties of manganese-doped (3HgSe)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(Al<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystals

The transport and optical properties of (3HgSe)_{1 − x} (Al₂Se₃) _x 〈Mn〉 crystals have been studied, and their energy-band parameters have been determined. The transport measurements were made by a four probe method in the ranges T = 77–300 K and H = 40–400 kA/m; transmission was measured at 300 K. The Hall coefficient of the crystals is temperature-independent, their electrical conductivity shows metallic behavior and is a nearly linear function of temperature, and their thermoelectric power increases with temperature. Optical data attest to direct allowed interband optical transitions and suggest that the electrons in the crystals are scattered predominantly by ionized impurities. The energy-band parameters are determined and are used to construct the energy-band diagram of the crystals.     

Growth and Electrical Properties of Pb1 – x Mn x Te Crystals

Pb_{1 – x} Mn _x Te single crystals were grown, and their electrical conductivity, thermoelectric power, and Hall coefficient were measured from 80 to 300 K. The results indicate that the transport properties of the crystals are determined by lattice defects, the structure of the valence band, and Mn content.     

CVT growth of zirconium sulphoselenide single crystals

Large single crystals of a few important members (x=0, 1, 2) of the series ZrS _x Se_2−x compounds have been obtained by chemical vapour (iodine) transport method. The crystals have been characterized for several properties. Their semiconducting nature is inferred from resistivity vs temperature measurements, their optical absorption data reveal indirect gap transitions, their thermoscans indicate their stability over a limited temperature range, and they essentially grow by the mechanism of two dimensional layer propagation.