Habit modification and improvement in properties of potassium hydrogen phthalate (KAP) crystals doped with metal ions

Potassium hydrogen phthalate (KAP) single crystals were grown by slow evaporation and slow cooling techniques. The growth procedure like temperature cooling rate, evaporation rate, solution pH, concentration of the solute, supersaturation ratio etc., has been varied to have optically transparent crystals. Efforts were made to dope the KAP crystals with rubidium, sodium and lithium ions. The dopant concentration has been varied from 0.01 to 10 mole percent. Good quality single crystals were grown with different concentrations of dopants in the mother phase. Depending on the concentration of the dopants and the solution pH value, there is modification of habit. Rubidium ions very much improve the growth on the prismatic faces. The transparency of the crystals is improved with rubidium and sodium doping. The role of the dopants on the non‐linear optical performance of KAP indicates better efficiency for doped crystals. The grown crystals were characterized with XRD, FT‐IR, chemical etching, Vickers microhardness and SHG measurements. The influence of the dopants on the optical, chemical, structural, mechanical and other properties of the KAP crystals was analysed. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Growth,spectral and thermal properties of KAP single crystals in the presence of DL‐Alanine and L‐Methionine amino acid dopants

Single crystals of potassium acid phthalate (KAP) and amino acid (DL‐Alanine, L‐Methionine) doped KAP were grown from aqueous solutions by slow cooling method. The grown crystals were characterized using powder X Ray diffraction (XRD) and Fourier Transform Infrared (FTIR) analysis. The thermal stability of KAP in the presence of dopants was analysed using Thermogravimetric and Differential Scanning caloriemetric (TGA/ DSC) studies and the maximum temperature for non linear optical application of this compound in the presence of dopants was found out. The transmittance of KAP was found to increase in the presence of dopants. Etch pits were observed for all the crystals using different etchants. Vickers microhardness tests were performed to study the mechanical stability of the crystals. The hardness of DL‐alanine doped KAP is more than that of L‐alanine doped KAP crystal. The dielectric constant and loss were determined as a function of temperature. Frequency response of the dielectric constant and dielectric loss factor have been studied over the frequency range of 50Hz – 5MHz. Second harmonic generation (SHG) was confirmed in all the crystals using the Kurtz and Perry powder technique. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the incorporation mechanism and distribution mode of impurities in potassium acid phthalate crystals grown from aqueous solutions

Mechanism of impurity structure formation in crystals grown from aqueous solutions has been studied on the example of potassium acid phtalate (abbreviated hereafter as KAP) single crystals. Gold decoration technique at an electronmicroscopic scale has been applied to the study of the distribution of uncontrolled impurities on KAP cleavage face (010) after 10, 20 and 30 days of growth, taking into consideration different growth rates in 〈001〉 and 〈001 〈 directions. A technique for visualization of impurities in water, based on the adsorption of these impurities by the surface of amorphous film of nitrocellulose (parlodion) and the vacuum decoration with gold of these impurities, has been developed. Differences in the impurity structure of KAP regions located in 〈001〉 and 〈001〉 directions from the seed have been established. In 〈001〉 direction after 20 days of growth impurity assemblies 0.1—0.4 μm in size are revealed, and in 〈001〉 direction heterogeneous impurity structure is revealed only after 30 days of growth. The real (impurity) structure of KAP outside impurity assemblies is quite homogeneous and is the same throughout the whole crystal volume, the impurities incorporating mainly into complex active centres. From comparison of the changes in time of the impurity structure of water used for crystallization solutions and the impurity structure of KAP crystals a conclusion is made that the impurity structure of crystals is “programmed” in the impurity structure of crystallization solutions which regularly changes with time, i. e. impurities from different kinds of assemblies which are selectively adsorbed by the growing crystal faces. The role of the adjacent to the growing face interfacial layers which control the growth rate and have a complex impurity structure is stressed.     

Crystal and molecular structures of potassium cobalt hydrogen phthalate K2[Co(H2O)6](C8H5O4)4 ⋅ 4H2O and mechanism of Co2+ impurity trapping in KAP crystals

The single-crystal X-ray diffraction analysis of K₂[Co(H₂O)₆](C₈H₅O₄)₄ ? 4H₂O has been carried out. The K₂[Co(H₂O)₆](C₈H₅O₄)₄ ? 4H₂O single crystals are obtained in attempting to grow the KAP crystals with the maximum possible content of Co²⁺ impurity cations. The crystals are isostructural to the earlier-studied similar crystals with Ni(II). The structure is formed by double layers of biphthalate anions and the Co²⁺ and K⁺ cations in between. The Co²⁺ cations are coordinated only by water molecules, whereas the coordination of the K⁺ cations involves both the biphthalate anions and water molecules. A detailed crystal chemical analysis, together with the data on the growth kinetics of KAP crystals in the presence of Co²⁺ and the mass-spectrometric data obtained earlier for the KAP crystals, leads to the conclusion that the Co²⁺ impurity cations should be located in the form of the [Co(H₂O)₆]²⁺ cationic complexes in the interblock layers of the KAP crystals.     

Morphological effects in liquid phase epitaxy (The C8H5O4K-C8H5O4Rb-H2O system)

The results of the complex study of the morphology and defect state of the crystals of the isomorphous potassium acid phthalate-rubidium acid phthalate (KAP-RbAP) series formed in aqueous solutions are presented. The crystals are characterized by heteroepitaxial porous and solid textures formed as a result of the exchange reaction between the crystals and solution. The interaction of the KAP and RbAP crystals with saturated RbAP and KAP aqueous solutions is studied both in situ and in vitro under optical and atomic force microscopes. The results obtained are used to create a theoretical model of formation of characteristic morphological textures in liquid phase epitaxy, including their formation from the aqueous solutions of the respective salts.     

A Novel Method to Enhance Metastable Zone Width for Crystal Growth from Solution

A novel method has been found to enhance the metastable zone width of solutions in their supersaturated region in order to grow large size crystals. In which, the incorporation of a small quantity of Ethylenediamine tetra acetic acid (EDTA), a well‐known chelating agent, enhances the zone width significantly due to its chelating action. Also this incorporation reduces the nucleation rate and enhances the growth rate of the crystal. X‐ray rocking curve experiment for the grown crystals reveals that EDTA addition does not affect the crystalline quality. This concept was first realized with Potassium acid phthalate (KAP) solutions and then confirmed with Potassium dihydrogen phosphate (KDP) and Triglycine Sulphate (TGS).     

The Czochralski growth of doped bismuth-germanium oxide (BGO) and bismuth-silicon oxide (BSO) single crystals

Doped single crystals of BGO and BSO with Cr, Mn, Cu, Ni have been grown. The conditions for the growth of doped single crystals by the Czochralski method have been determined, analyses of distributions of dopants in the crystals have been made. For the Mn, Cr, Cu, doped crystals changes of coloration after illumination with visible light have been observed.     

Morphology of PbI2 Crystals Grown by Gel Method

The single crystals of Lead Iodide have been grown by gel method. X‐ray diffraction studies on these crystals shows that the lattice parameters of grown crystals are almost matching with reported values. The results of detailed studies made on the microstructures of Lead Iodide crystals, have been described. The observations of the faces of these crystals revealed that they have grown by layer as well as spiral mechanisms. The probable role of these parameters is explained along with the surface microstructures on these various shaped crystals.     

Stoichiometric dependence of electrical characteristics in WSSe single crystals grown by direct and chemical vapour transport techniques

Single crystals of tungsten sulphoselenide (WSSe) have been grown by both direct and chemical vapour transport techniques. The crystals have been subjected to Hall effect and resistivity measurements for their electrical characterization. The observed differences in the electrical resistivity, type of conduction, and activation energy have been attributed to the stoichiometric differences between the crystals grown by the two techniques. The crystals grown by chemical vapour transport technique with iodine as the transport agent have been found to be more stoichiometric.     

Investigations of the growth mechanism and morphology of silver crystals grown electrolytically in gels

Gel medium has been used for the electrolytic growth of silver dendrites and single crystals of a variety of morphological features and forms. Microtopographic studies of the crystals have been carried out using optical and scanning electron microscopes. Some unusual growth surface morphologies have been observed. The surfaces of some of the crystals have a high degree of perfection. Sufficient experimental evidences are obtained for the striated growth of crystals and twin plane re-entrant edge (TPRE] mechanism of growth. The formation of tertiary three-dimensional (T3D) dendrites and dendrites with obliquely forward and backward branchings at different stages of growth have been investigated.     

Electrical and photoelectrical properties of chalcopyrite n-AgInS2 crystals

The chalcopyrite n-type crystals have been grown from AgInS₂ material having stoichiomtric Ag excess. The temperature dependence of the Hall effect in these crystals have been studied. The ionization energies of donors have been determined. The dependence of the photoconduction on the photon energy, the light intensity and the temperature in the n-AgInS₂ crystals have been measured. The recombination model of photoconductor with one class of recombination centres has been proposed for explanation of the photoelectrical results.     

Growth and properties of calcium tungstate

CaWO₄ single crystals have been grown and compared by three different high temperature solution methods, viz. the normal flux-cooling procedure, the indirect flux-reaction technique and the isothermal flux-evaporation method. The typical as-grown bipyramidal crystals obtained by these methods have been found to be mostly large and perfect with varying degree of transparency. The crystals are characterised by using EDAX, X-ray diffraction, electrical conduction, micromechanical tests and chemical etching. The assessment of various characteristics of the grown crystals is likely to show enormous usefulness of the flux grown crystals.     

Effect of Flux on thermoluminescence in Flux-grown BaFCl crystals

BaFCl crystals have been grown using BaF₂ and BaCl₂ by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF₂ flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.     

Synthesis and growth of PbTe crystals at low temperature and their characterization

Lead telluride crystals have been grown for the first time by the cold traveling heater method. The structural properties of the crystals have been studied by neutron diffraction, and rocking-curves with a full-width at half-maximum of about 36 arcsec have been measured, indicating a very weak mosaicity. The lattice parameter of the crystals has been found to be ∼0.64618±0.00004 nm by X-ray diffraction. Vickers microhardness in the range 25–30 kg/mm² have been measured, depending on the charge applied to the crystals. The electronic properties of the crystals, either as-grown or annealed, have been measured and demonstrate their very high purity level, as expected from the low-temperature growth and purification process by traveling heater method. Finally, the potentialities of PbTe as a substrate for the growth of HgCdTe layers are discussed in the light of all the results reported.     

PVT and CVT Growth and Characterization of SnSxSe2-x (0 ≤ x ≤ 2) Single Crystals

Single crystals of solid solutions of tin sulphoselenide have been grown in the same ampoule. Specific conditions for growing single crystals of SnSSe have also been identified. A study of microstructures on the growth surfaces responds to the mechanism of growth of these crystals. The dependence of electrical resistivity, Hall mobility and carrier concentration with the values of the configuration parameter 2 has been studied.     

Growth and Characterisation of Pure and Nickel-doped Strontium Tartrate Tetrahydrate Single Crystals

Strontium tartrate tetrahydrate single crystals doped with nickel have been grown in silica gel. The grown crystals have been characterized by X-ray, atomic absorption spectroscopy (AAS), thermogravimetric analysis (TGA), and etching technique.     

Strength of Crystals of Small Dimensions and their Triboluminescence

Stress-dependence of triboluminescence (TBL) in uranyl nitrate, tartaric acid and other nine crystals has been studied with the help of a new technique of crushing the crystals. As the appearance of TBL needs the creation of new surfaces in a crystal, the minimum stress at which TBL appears has been taken to be the fracture-strength of the crystal. The value of the fracture-strength and stress coefficient of binding energy determined from TBL measurements are found to be of correct order. It has been found that the rate of rise of TBL intensity with stress is higher for those crystals which have less value of the fracture-strength. The fracture strength (σ_f) is found to be higher for those crystals which have less value of stress coefficient of binding energy (β) and the product of σ_f and β is higher for those crystals which have higher melting point. It has been shown that the rate of rise of TBL intensity with stress decreases at higher values of stress due to strain hardening in the crystals.     

Microstructures on {111} faces of stannic iodide single crystals

Single crystals of stannic iodide (SnI₄) havebeen grown using the controlled reaction between SnCl₂ and KI by diffusion process in silica gel medium. Orange to reddish octahedral stannic iodide crystals up to 3–4 mm in size have been grown at room temperature. Optical studies have been made on the various surface structures of {111} faces of the asgrown crystals. On octahedral faces of these crystals, triangular-shaped hillocks with growth layers in the 〈110〉 directions have been observed. Occasionally, growth spirals on octahedral faces have also been reported. Close loops of growth fronts have been investigated and have been interpreted. It has been suggested that two-diemensional nucleation, spreading and pilling up of triangular growth layers is mainly responsible for the growth and occasionally the growth is due to screw dislocations. The implications are discussed.     

Li离子浓度对铌酸钾锂晶体[NbO6]7-八面体畸变的影响

用顶部籽晶法生长了一批不同组成的铌酸钾锂晶,用同步辐射X射线分析了晶体结晶特性,用Philips PW2400 X射线荧光光谱法测量了晶体的组成.对三种组成的晶体样品测量了红外拉曼光谱,分析了晶体中组分离子浓度对晶体红外拉曼光谱特征的影响,结果表明,晶体中位于C格位的Li离子浓度对晶体拉曼光谱产生了强烈的影响,影响的本质在于晶体中Li含量的提高导致晶体中[NbO6]7-八面体畸变程度加大,对八面体晶格振动产生了强烈的影响.