Investigation on growth and characterization of a new inorganic NLO material: Zinc sulphate (ZnSO4:7H2O) doped with Magnesium Sulphate (MgSO4:7H2O)

Single crystal of Zinc sulphate doped with Magnesium sulphate, a nonlinear material, was grown from aqua solution by slow evaporation method at room temperature. Good quality single crystals were grown by slow evaporation technique (four weeks) and the crystals subjected to single crystal X-ray diffraction and FT-IR analyses to confirm the formulation of new crystals. The TGA and DTA reveal that the material has good thermal stability. The UV-Vis spectrum confirms that the material has wide optical transparency and the existence of the second harmonic generation has also been ascertained by Kurtz powder method.     

Special features of growing diamond single crystals in the Fe-Co-Zr-C system

The results have been considered of the investigations into the effect of various concentrations of zirconium addition to the Fe-Co alloy solvent on the growth rate and habit of a diamond single crystal grown by the temperature gradient method in the diamond thermodynamic stability region. The dependence of the defect and impurity state of grown crystals on the percentage of the zirconium addition has been established. The maximum zirconium content and temperature of the alloy solvent, which provide the growth of structurally perfect type IIa diamond single crystals, have been defined.     

Interatomic bond energy and analytical scale of hardness

Based on detailed models of interatomic cohesion and the well-developed structural-thermodynamic approach, the interatomic bond energy has been determined for some covalent and metallic crystals and it has been found to agree with experimental data. Using the proposed analytical relationship for the degree of covalency of crystals the author has elaborated a generalized model that describes experimental hardness of supersclerometer materials (diamond, cBN, SiC, and others), minerals, refractory compounds, semiconductors, ionic crystals and metals. On the basis of the mechanical-chemical approach to (nano)flow a dislocation model of crystal-mechanical anisotropy of yield strength has been put forward for monocrystalline diamond and lonsdaleite; the model makes it possible to draw a conclusion on a slight difference in their sclerometric characteristics. The experimental relationships that govern high-temperature high-pressure plasticity in some covalent crystals are discussed.     

Effect of frictional forces on the behaviour of dislocation loops

A detailed analysis of the effect of frictional forces on the stability of dislocation loops lying in their glide planes and the effect of these forces on the cross-slip behaviour of these loops under both applied stresses as well as internal stresses arising from other dislocation loops, has been made. In addition, the passing as well as cross-slip behaviour of non-coaxial dislocation loops has been analyzed and it is shown that these loops could give rise to Frank-Read sources by way of cross-slip; and the conditions for generations of such Frank-Read sources have been determined. The results show that depending upon strain, the cross-slip of dislocation loops could lead to regeneration of dislocation and subsequent work-hardening, or to dynamic recovery or stage III deformation. The significance of the above results in relation to the behaviour of dislocation loops observed in real crystals is discussed in detail.     

Effect of Metastable Phases on the Structural Perfection of Single Crystals of Stable Bismuth Oxide Compounds

It is shown that a detailed understanding of metastable phase relations is crucial for the ability to grow perfect Bi₄Si₃O₁₂ and Bi₄Ge₃O₁₂ single crystals by the Czochralski process. The high stability of metastable states in melts of bismuth-oxide-containing systems has a marked effect on the structural perfection of the growing crystals of stable compounds. Crystals containing inclusions of metastable phases are grown from overheated melts.     

The growth of benzophenone crystals by Sankaranarayanan–Ramasamy (SR) method and slow evaporation solution technique (SEST): A comparative investigation

Longest unidirectional〈1 0 0〉 benzophenone (BP) crystal having dimension of 1060 mm length and 55 mm diameter was grown by Sankaranarayanan–Ramasamy method. The growth rate was measured by monitoring the elevation of the crystal–solution interface at different temperatures. The high resolution X-ray diffraction and etching measurements indicate that the unidirectional grown benzophenone crystal has good crystalline perfection and less density of defects. The optical damage threshold of SEST and SR grown BP crystals has been investigated and found that the SR grown benzophenone crystal has higher laser damage threshold value than the conventional method grown crystal. Microhardness measurement shows that crystals grown by SR method have a higher mechanical stability than the crystals grown by SEST method. Dielectric permittivity and birefringence are high in SR grown crystal compared to SEST grown BP crystal. The UV–vis-NIR results show that SR method grown crystal exhibits 7% higher transmittance as against crystals grown by conventional method.     

Perturbation analysis of high strain-rate shear localization in B.C.C. crystalline materials

Summary A perturbation analysis has been used to obtain a detailed and fundamental understanding of the high strain-rate material mechanisms associated with material instabilities and adiabatic shear-band formation in single body-centered cubic (b.c.c.) crystals. The interrelated effects of wave number, shear-band orientation, strain hardening, strain-rate sensitivity, and thermal and geometrical softening on material instability and shear-strain localization have been investigated in terms of the competition between the softening and hardening mechanisms for nominal strain-rates from 100/s to 5000/s. A perturbed system of equations has been obtained, accounting for arbitrary crystal orientations, and since no approximations have been made for the magnitude of the strain-rate sensitivity parameter, all the roots associated with the stability of the perturbed equations can be obtained for physically representative deformations. Hence, a comprehensive characterization of material instabilities can be obtained beyond the initial instability point, and the strength of material instabilities can be then monitored throughout the deformation history to distinguish between material instabilities and shear-strain localization.     

Specific Heat and Interface Energy of Nanostructured ZrAlNiCuCo Alloy

The specific heat of the nanostructured crystals, the glass, the liquid and the crystals for a ZrAINiCuCo alloy has been measured by using the differential scanning calorimeter. The specific heat value and its temperature coefficient of the nanostructured crystals are larger than that of the relaxed glass and of the crystals. Through measuring crystallization enthalpies and specific heat of the alloy in different states, the enthalpy difFerences among the crystals, the liquid and the nanostructured crystals are calculated and the intedece energies of nanostructured crystals are estimated. The stability and the grain size limit of the nanostructured crystals are discussed.     

Growth and thermal studies of SnSe single crystals

Single crystals of SnSe have been grown by a direct vapour transport (DVT) technique. The confirmation of single crystallinity and lattice parameter determination of the grown crystals have been made by using electron and X-ray diffraction techniques respectively. The thermal analysis of the crystals has been studied by the well known TGA and DTA techniques. The results obtained during the analysis showed the stability of SnSe phase at higher temperatures. The implications of the results have been discussed.     

Effect of twins on deformation of graphite single crystals

A detailed investigation has been made of deformation and fracture in graphite single crystals, between 20 and 2400° C, under a tensile stress parallel to the basal plane. Crystals are shown to be inherently weak when twins are present and the low value of modulus recorded in twinned crystals is attributed to dislocation glide within these regions. A mechanism of fracture is proposed which is consistent with the low strength and the fracture characteristics of graphite.It has been shown that graphite single crystals exhibit anomalous behaviour in that the tensile fracture strength increases if tests are made at temperatures greater than 2000° C.This increase in strength is associated with the movement and annihilation of twin boundaries and subsequent reduction in stress concentration. Delamination is also shown to result from twin boundary movement.     

Investigation on growth,structural, optical,thermal, dielectric and mechanical properties of organic l-prolinium trichloroacetate single crystals

A new organic nonlinear optical material l-prolinium trichloroacetate (l-PTCA) single crystal has been synthesized and grown by slow solvent evaporation technique at room temperature using water as solvent. Single-crystal X-ray diffractometer was utilized to measure unit cell parameters and to confirm lattice parameter. The powder X-ray diffraction pattern of the grown l-PTCA has been indexed. The modes of vibration of different molecular groups present in the sample were identified by the FTIR spectral analysis. The optical transmittance window and the lower cutoff wavelength of the l-PTCA have been identified by UV–vis–NIR studies. Thermal stability of the l-prolinium trichloroacetate was determined by TGA/DTA measurements. Dielectric measurements were carried out at various temperatures at frequency range 10–1 MHz. The mechanical properties of the grown crystals have been analyzed by Vickers microhardness method. The chemical etching studies were carried out on the grown crystals. Its SHG efficiency has been tested by Kurtz powder method.     

Time-dependent, protein-directed growth of gold nanoparticles within a single crystal of lysozyme

Gold nanoparticles are useful in biomedical applications due to their distinct optical properties and high chemical stability. Reports of the biogenic formation of gold colloids from gold complexes has also led to an increased level of interest in the biomineralization of gold. However, the mechanism responsible for biomolecule-directed gold nanoparticle formation remains unclear due to the lack of structural information about biological systems and the fast kinetics of biomimetic chemical systems in solution. Here we show that intact single crystals of lysozyme can be used to study the time-dependent, protein-directed growth of gold nanoparticles. The protein crystals slow down the growth of the gold nanoparticles, allowing detailed kinetic studies to be carried out, and permit a three-dimensional structural characterization that would be difficult to achieve in solution. Furthermore, we show that additional chemical species can be used to fine-tune the growth rate of the gold nanoparticles.     

Growth and characterization of a new non-linear optical l-histidinium dihydrogen phosphate single crystal

New non-linear optical single crystal of l-histidinium dihydrogen phosphate was grown by slow evaporation and temperature lowering technique from aqueous solution. Solubility studies have been carried out for three different solvents (water, acetone and ethanol). The grown crystals have been subjected to single crystal X-ray diffraction analysis to identify the cell parameters and morphology. Optical transmission spectra reveal the optical properties of the grown crystals. The NLO property of the crystal has been confirmed by Kurtz SHG test. Comparing the output power it has been confirmed that l-HDP crystals possess higher SHG efficiency than KDP. Thermal studies were carried out to check the thermal stability of the crystals.     

Micromorphological studies on the ZnSe single crystals grown by chemical vapour transport technique

Single crystals of ZnSe have been grown by chemical vapour transport technique. Microscopic observation of crystal surfaces has been carried out using optical microscope and scanning electron microscope (SEM). Different micromorphological patterns such as microsteps, spirals and kinks were observed on the surface of the grown crystals in different growth conditions. Present studies show that the formation of these microstructures on the surface of the grown crystals depends on the growth parameters such as undercooling and stability of the growth interface. The morphology and lattice parameters of the grown crystals have also been determined by X-ray analysis.     

Compounds and solid solutions of the Zn-Cd-P-As system in semiconductor electronics

Using the constructed pseudobinary joins and phase equilibria in the Zn-Cd-P-As system, we have determined the stability regions and space groups of ternary and quaternary solid solutions. Evidence is presented that orthorhombic cadmium diphosphide does not exist. Based on detailed studies of the physicochemical properties of II–V crystals, we have proposed and fabricated a number of electronic devices.     

Growth by SR method and characterization of bis(thiourea)zinc(II) chloride single crystals

Large size single crystals of bis(thiourea)zinc(II) chloride (BTZC), a potential nonlinear optical material, have been grown successfully by the Sankaranarayanan-Ramasamy (SR) method. Powder X-ray diffraction and Fourier transform infrared analyses confirmed the material of the grown crystal. Thermal stability was assessed by the thermogravimetric/differential thermal analysis. The high-resolution X-ray diffraction and dielectric measurements indicate that the crystal grown by the SR method has good crystalline perfection and low density of defects.     

Effect of cobalt (Co<Superscript>2+</Superscript>) concentration on structural,optical, thermal and mechanical properties of potassium acid phthalate (KAP) crystals

Single crystals of pure and Co²⁺ (0.2, 0.4 and 0.6 mol%) doped KAP crystals were grown by low temperature slow evaporation method. The grown crystals were subjected to various characterization techniques such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV–visible spectroscopy and Second Harmonic Generation studies. The XRD profile confirms that Co²⁺ ions incorporated into the KAP crystal lattice. The existence of functional groups in the grown crystals have been studied by FTIR analysis. Optical transmission is decreased when doping Co²⁺ concentration increase. After melting point, no decomposition is found in the pure crystal. Vickers micro hardness studies revealed that the doped crystals possess very high hardness values. The dielectric constant, dielectric loss and thermal stability values have been measured as a function of frequency and temperature respectively for the doped crystals.     

Organization of the production of 100 tons of lead tungstate crystals for the CMS experiment at CERN

The CMS collaboration at CERN has undertaken at the end of 1994 an ambitious R&D program on Lead Tugstate scintillating crystals for its electromagnetic calorimeter. All the parameters of this crystal have been extensively studied in order to optimize its performances in the context of the Large Hadron Collider. Full size crystals (23 cm in length, up to 2.5 × 2.5 cm² in section) with the desired trapezoidal geometry can now be grown and mechanically processed with a yield in excess of 80%. A thorough investigation of the raw material preparation and of the growing conditions has led to a significant improvement in the optical transparency and in the light yield of the crystals. A detailed understanding of the light emission mechanism was 1995. A systematic analysis of the parameters influencing the structural quality of the crystals was at the origin of a considerable improvement of the radiation hardness of full size crystals. All these progress will be illustrated by results of measurements on a statistically representative number of crystals. The conditions of these improvements will be discussed in the context of the mass production of more than 80,000 crystals in a cost effective way.     

A Comparison between TGT and Cz Grown Nd：YAG

Large sized neodymium-doped Y3Al5O12 （Nd：YAG） laser crystals have been grown by temperature gradient technique （TGT） method and compared with Czochralski （Cz） method. The comparison of these two crystal growth methods has been listed. The results showed that the TGT method has many advantages over the Cz method. The concentration distribution of Nd ions in the crystals was determined and the absorption spectra of these crystals have been investigated and compared. The TGT grown highly doped Nd：YAG crystal has a larger absorption FWHM than that of Cz grown Nd：YAG crysral. Highly doped Nd：YAG （～2.8 at. pct） crystals could be obtained by TGT.