Effect of indium intercalation on various properties of MoSe2 single crystals

Indium intercalated MoSe₂ single crystals i.e. In_xMoSe₂ (0 ≤ x ≤ 1) are grown by direct vapour transport technique. These crystals are structurally characterized by X‐ray diffraction, by determining their lattice parameters ‘a’ and ‘c’ and X‐ray density. The Hall effect and thermoelectric power measurements shows that In_xMoSe₂ (0 ≤ x ≤ 1) are p‐type in nature. The direct and indirect band gap measurements are also undertaken on these semiconducting materials. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoelastic and X-ray topographic studies of residual stress and lattice deformation in GaAs single crystals

The GaAs crystals, grown with three different methods were simultaneously studied by means of photoelastic and X-ray topographic methods. The methods provide complementary information about lattice deformation. The correspondence between interplanar distance changes and photoelastically measured stress values and the connection between cellular structure and high stress values were also found.     

Surface topographical studies of prism faces of ammonium tartrate single crystals

A study of surface structures of Prism faces (110) of ammonium tartrate single crystals grown by gel technique is described and illustrated. Vertical striations closly and widely spaced are observed. Isolated as well as densely populated rectangular elongated hillocks are reported and mechanism of the growth of these faces is assessed in the light of observed surface structure.     

X-ray topographic studies of the melting of nearly perfect gallium crystals

The temperature dependence of the concentration and shape of long dislocation lines in pure, nearly perfect gallium crystals has been measured by X-ray topography in anomalous transmission (Borrmann-topography). The dislocation structure did not change appreciably between temperatures of 22°C and at least 0.1 mK below the melting point T_m = 29.75°C. A few dislocations decreased their length due to tempering at the melting point. Pre-melting effects could not be detected.     

Dielectric studies on sodium fluoroantimonate single crystals

Dielectric properties of grown single crystals of Na₂SbF₅ and Na₃Sb₂F₉ have been carried out. The values of the dielectric constant of Na₂SbF₅ and Na₃Sb₂F₉ are about 24.1 and 14.3, respectively, at temperatures from 30 °C to 250 °C and 225 °C for 100 kHz.     

Dielectric studies of lead nitrate phosphate single crystals

Ferroelectric Lead Nitrogen Phosphate (LNP) single crystals have been synthesized using the controlled reaction between lead nitrate and orthophosphoric acid solutions by slow diffusion process in silicagel medium. The colourless transparent LNP crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The dielectric measurements have been carried out in the temperature range between 300 to 690 K. The effect of applied frequency on the dielectric constants and dielectric losses has been investigated. It has been observed that the mechanism of the dielectric behaviour is different in the lower and higher frequency and temperature ranges. The activation energy of the oscillators has been calculated and found to be 1.125 eV. Attempt has been made to draw some qualitative conclusions, taking in view, the existing theories of various kinds of polarizations and implications.     

Microhardness studies of ammonium hydrogen tartrate single crystals

Single crystals of ammonium hydrogen tartrate AHT NH₄HC₄H₄O₆ have been grown employing the controlled reaction between NH₄Cl and (CHOHCOOH)₂ by slow diffusion process in silica gels. The variation in the microhardness of AHT crystals has been determined using Vicker's microhardness indentor. The effects of annealing and quenching on the mechanical properties of these crystals have been studied. It is observed that: (i) irrespective of the relative orientation of the indentor and the crystal, the median vents initiated at the sharp indentation edges, (ii) the microhardness of the crystals depends on the applied load, (iii) the microhardness of the crystal is independent on the duration of loading, and (iv) maximum plasticity is observed in quenched crystals. The implications of this behaviour are discussed.     

On growth and morphological studies of TGS single crystals

The effect of various growth parameters; seed morphology, growth-temperature and pH of the mother solution on the growth of TGS single crystals is studied. The effect of these variables on the crystal morphology and perfection is reported. It is shown that; (i) The crystal quality is much dependent on the seed and the growth temperature and (ii) the pH-control is a simple and an effective method for obtaining TGS crystals of required morphology.     

DC conductivity studies in K3Na(SeO4)2 single crystals

DC electrical conductivity studies were carried out along the three crystallographic axes for Tripotassium sodium diselenate (K₃Na(SeO₄)₂ or KNSe). Earlier studies of phase transition in this crystal show successive phase transitions at 334 K, 346 K, 730 K, and 758 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303 K – 430 K along a, b and c – axes. An anomaly in conductivity was obtained around 341 K and another one around 333 K. These can be attributed as due to phase transitions in this crystal. A strong anomaly also has been observed along the c‐axis and comparatively week one along a and b axes around 395 K for the first time. This can be due to newly observed phase transition in the crystal. DSC taken for the sample also shows endothermic peak supporting the occurrence of newly observed phase transition. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deformation and microhardness studies on KClO4 single crystals

The deformation characteristics of KClO₄ single crystals have been studied by the methods of static and dynamic indentation on (001) plane. The cracks produced by the dynamic indentation have been interpreted in terms of slip-twin interactions. Also, the load dependence of Vickers microhardness and its anisotropy in this crystal are reported. The observed hardness anisotropy has been used to confirm the indices of the slip system 〈101〉 〈111〉 operative in this crystal at ordinary temperatures.     

Microscopic studies on imperfections in selected YAB single crystals

The as‐grown surface and inner structures of undoped and Nd³⁺‐, Cr³⁺‐, V³⁺‐, Ce³⁺‐, Er³⁺ and Yb³⁺ – and (Er³⁺ + Yb³⁺) – doped yttrium aluminum borate (YAB) single crystals grown from (K₂Mo₃O₁₀ + B₂O₃) flux by spontaneous crystallization or top seeded solution growth (TSSG) technique, were investigated using optical and scanning electron microscopic and analytic chemical methods. Fine and rough growth hillocks of dislocational origin, growth layers, traces of inner planar defects and foreign phase crystalline debris were found and analyzed on the as‐grown faces of crystals. Irregular grains and regular block structures and foreign phase inclusions were observed and studied in the interior of the crystals. The chemical compositions measured by energy dispersive X‐ray spectrometry on perfect and imperfect micro regions are compared with those obtained by flame atomic absorption spectrometry on bulk crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and dielectric studies on succinic acid single crystals

Single crystals of ferroelectric succinic acid (SA) with very high degree of transparency were grown from aqueous solution by slow evaporation technique. Single crystal X‐ray diffraction analysis reveals that the crystal belongs to monoclinic system with the space group P2₁/c. Some physical parameters have been determined for grown crystal. The optical absorption study reveals the transparency of the crystal in the entire visible region and the cut off wave length was found to be 240 nm. The optical band gap is found to be 3.75 eV. The dependence of extinction coefficient (k) and refractive index (n) on the wavelength have also been reported. The presence of functional groups was determined qualitatively by using Fourier transform infrared spectrum (FTIR) from which force constant has been calculated. The dielectric constant was also studied as a function of frequency at room temperature and electrical conductivity has been calculated from the Cole‐Cole plot. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray and Raman studies of single crystals of CsSbF6

Crystals of CsSbF₆ belong to the rhombohedral space groupR¯3-C _3i ² witha=7.904(1)andc=8.261(1) Å,V=446.95 ų,Z=3,D _c=4.11 gcm^–3. The antimony atom is surrounded by six fluorine atoms in a nearly perfect octahedral configuration with Sb-F 1.875(9) Å, while 12 fluorine atoms surround the cesium atom with closest contact 3.116 Å. Polarized Raman spectra of single crystals of CsSbF₆ have been obtained, and it is shown that these results can be interpreted in terms of a unimolecular rhombohedral structure. The small distortion from an octahedral arrangement for the SbF ₆ ^– group is clearly reflected in the spectra. The Raman results are in better agreement with the space groupR¯3m-D _3d ⁵ than withR¯3-C _3i ² , but this conclusion must be regarded with caution since the two features in the vibrational spectra of CsSbF₆ which can be used to distinguish between the two structures are weak and ill-defined.     

Oxidation kinetics of BaF2 single crystals

Oxidation of BaF₂ single-crystals as a result of annealing in air in the temperature range 600° to 900 °C leads to mechanical strengthening. The process kinetics was investigated. It is shown that oxidation takes place in the bulk of crystals owing to oxygen diffusion by formation and growth of oxidation centres. These centres are precipitates of a BaO phase which were revealed by chemical etching.     

Analysis of current ‐ voltage ‐ temperature characteristics of In and Cu contacts on n‐type MoSe2 single crystals

The current voltage characteristics of In / Cu with n‐type MoSe₂ Schottky diodes were measured over a wide temperature range 50 < T < 300 K. The interface formed by In and MoSe₂ shows ohmic behavior after annealing the contact at 100 °C for 12 h. The ohmic nature was retained at all the measured temperatures. The Cu ‐ nMoSe2 interface formed a Schottky junction diode with a good rectification ratio. The Schottky barrier height and the ideality factor thereby obtained were 0.72 eV and 1.45, respectively, at room temperature. Below room temperature, the barrier height and the ideality factor vary with decreasing temperature. The changes are significant at low temperatures. Barrier height inhomogeneities at the interface cause deviation in the zero‐bias barrier height and the ideality factor at low temperatures, and produce extra current such that I‐V characteristics remain consistent with the thermionic emission mechanism. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and microscopic studies of yttrium aluminium garnet single crystals

A study has been made to understand the growth history and growth mechanism of flux grown yttrium aluminium garnet (YAG) single crystals. Etching has been done to reveal the growth patterns of flux grown crystals. Optical and scanning electron micrographs are presented. Optical micrographs were taken under polarised light and oblique incident light. The nature and origin of growth hillock is elucidated.