Growth of CaMoO4 and SrMoO4 crystals in silica gel media

Growth kinetics and characterization of calcium and strontium molybdate crystals grown in silica gel have been studied under a variety of parameters. The changes in nucleation characteristics, growth habit, quality of these crystals were carefully observed and are found directly related to pH of the medium. The profound influence of pH on spontaneous crystallization of CaMoO₄ crystals has been carefully investigated; and its crystallization range has been determined. The wide morphological change of SrMoO₄ with respect to pH variation has been studied. The quality of the crystals has been critically examined.     

Chemical kinetics of dissolution of BaMoO4 crystals

An etchant capable of revealing the sites of dislocations in the flux-grown crystals of BaMoO₄ has been established. Using this etchant (HNO₃), effect of etching time, acid concentration and temperature on the selective etch rate is demonstrated. It is established that the process of dissolution in unstirred HNO₂ solutions is one of the diffusion rate controlled; an empirical equation governing the kinetics has been suggested.     

Periodic precipitation of barium molybdate in silica gel

The mechanism of formation of the rhythmic pattern of precipitate of barium molybdate in one-dimensional Liesegang phenomena is investigated quantitatively. They rhythmicity is found to be influenced by the molarity of inner and outer electrolytes and pH of the gel medium. The ‘time-law’, ‘spacing-law’ and ‘Δx-law’ are verified.     

On the morphology of BaMoO4 crystals: A theoretical and experimental approach

BaMoO₄ crystals were obtained by a co‐precipitation method, and their structures were characterized by X‐ray diffraction and Rietveld refinement techniques. Field emission scanning electron microscopy was utilized to investigate the morphology of the as‐synthesized aggregates.‐ Through systematic first principle calculations within the density functional theory method at the B3LYP level, we investigated the structure; the surface stability of the (001), (101), (110), (100), (111), and (112) surfaces; and the morphological transformations of BaMoO₄. The relative surfaces energies were further varied to predict a complete map of the available morphologies through a Wulff construction approach. This revealed that the obtained experimental and theoretical morphologies coincided when the surface energy values of the (001) surface decreased while those of the (100) and (101) facets increased simultaneously. Analysis of the surface structures showed that the electronic properties were associated with the presence of undercoordinated [BaO_x] (x = 4, 5, and 6) and [MoO_y] (y = 3) clusters. The presented results provide a comprehensive catalog of the morphologies most likely to be present under realistic conditions, and will serve as a starting point for future studies on the surface chemistry of BaMoO₄ crystals.     

Growth of different habits of lead bromide crystals in silica gel by the new gel technique

Lead bromide crystals of high optical perfection and of different habits have been grown in silica gel by new gel technique starting from colloidal lead tartrate and KBr solution. pH is found to be not a factor for habit modification. Certain habits of the grown crystals exhibit interesting surface features. The growth conditions have been optimized and the various aspects of the growth process have been widely investigated.     

Electrical Conductivity of BaMoO4 Single Crystals

Electrical conductivity measurements have been made on the flux grown barium molybdate single crystals in the temperature range 425 to 1000 K. The mechanisms of conduction in the region of lower and higher temperatures have been distinguished.     

Growth and characterization of mixed neodymium praseodymium oxalatze decahydrate crystals in silica gel

Mixed single crystals of neodymium praseodymium oxalate decahydrate were grown from silica gel by controlled reaction of rare earth nitrates with oxalic acid. The crystals were characterized using X-ray powder diffraction and optical absorption studies.     

Characterization of lead(II)chloride single crystals grown in silica gel

Acousto‐optical materials play an important role in acousto‐optic devices as acousto‐optic modulators. Lead(II) chloride is an acousto‐optical material, having high figure of merit approximately ten times greater than that of lead molybdate, which is an efficient acousto‐optical material. It also possesses high birefringence, low attenuation coefficient, wide transparency range and good mechanical properties. This paper discusses in detail, the growth of single crystals of lead(II) chloride in silica gel by the process of diffusion in a highly acidic medium. Needle‐type lead(II) chloride crystals have been obtained. The crystal system is confirmed to be orthorhombic by powder X‐ray diffraction analysis. To study the optical transparency of the grown crystal, the transmission spectrum has been recorded in the range 190 – 1100 nm. Thermal stability of the crystal is also studied. Results are discussed in detail. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of pure and doped potassium hydrogen tartrate single crystals grown in silica gel

Growth of pure‐, sodium‐ and lithium‐ doped potassium hydrogen tartrate single crystals by gel technique is reported. Growth conditions conducive for the growth of single crystals are worked out. The crystals are characterized by using powder XRD, SEM, FTIR, AES, EDAX, CH analysis and thermoanalytical techniques. The stoichiometric composition for the grown crystals are established as KHC₄H₄O₆.H₂O, (K)_0.98(Na)_0.02.H₂O and (K)_0.94(Li)_0.06HC₄H₄O₆.H₂O. Doping of sodium and lithium in the pure potassium hydrogen tartrate single crystals is found to influence the size, perfection, morphology, crystal structure and the thermal stability of crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observations on the growth of NiMoO4 crystals in Silica gel media

Growth of NiMoO₄ crystals by gel method has been described. By manipulating the condition of growth parameters, crystals of fairly large dimensions have been obtained at ambient temperature. The crystal faces are examined by optical and scanning electron microscopy and thus a two-dimensional layer growth mechanism for the development of the faces have been proposed.     

Growth of crystals of calcium sulphate in silica gel in presence of additive and their characterisation

Procedure for the growth of calcium sulphate dihydrate crystals in silica gel, in the presence of barium chloride as additive, is described. Optimum conditions for the growth of good quality crystals are worked out. The crystals are characterised by laser Raman spectroscopy, infrared spectroscopy, thermogravimetric analysis and Atomic absorption spectroscopy. It is shown that crystals in the presence of the additive have a greater degree of perfection than those without additive. Amount of water in the crystals is estimated as 20.97%. Presence of calcium and absence of barium in the crystals are indicated.     

Growth and characterization of pure and doped lead hydrogen phosphate single crystals in silica gel

Following the chemical reaction method pure and doped lead hydrogen phosphate single crystals were grown in silica gel using different gel density, various concentrations of phosphoric acid, and lead nitrate solutions. As the gel pH plays an important role in the formation of different H₃PO₄ species in the phosphoric acid system, the pH range in which HPO ions dominate, was considered which in turn in necessary for the growth of lead hydrogen phosphate crystals. Characteristics of these crystals were carried out by infrared spectral analysis and microhardness study.     

Study of crystalline perfection and thermal analysis of zinc cadmium thiocyanate single crystals grown in silica gel

Zinc cadmium thiocyanate ZnCd(SCN)₄ abbreviated as ZCTC is a bimetallic thiocyanate complex that exhibits excellent nonlinear optical property. Single crystals of ZCTC have been grown in silica gel by the process of diffusion. Colorless transparent crystals of size 12 mm x 2 mm x 1.3 mm have been obtained. High resolution X‐ray diffraction study was carried out to investigate the crystalline perfection of the grown crystal and the quality of the crystal was found to be quite good. Thermal stability of the grown crystal was investigated by thermogravimetric and differential thermal analyses. Fourier Transform Infrared spectrum was recorded to confirm the functional groups. Microhardness of the crystal is also studied. Being a nonlinear optical material, a comparative study of its second harmonic generation efficiency with urea has been made. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A comparative study of pure and potassium doped cadmium mercury thiocyanate single crystals grown in silica gel

Pure and potassium doped cadmium mercury thiocyanate single crystals have been obtained from silica gel by the process of diffusion. The X‐ray diffraction studies reveal the crystal lattice of both pure and doped crystals to be tetragonal. The crystalline perfection of the grown crystals were investigated by high resolution X‐ray diffraction analysis and the quality of the crystals are found to be extremely good. Transmission and Fourier transform infrared spectra were recorded for the grown crystals. The TG/DTA analyses show that the crystals are highly thermally stable. The mechanical strength of the crystals were studied by Vickers microhardness test and a study of their second harmonic generation efficiency in comparison with urea has been made by performing Kurtz powder test. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diffusion of gases in porous silica gel

Gas diffusion in porous silica gels prepared by the sol-gel process is studied at room temperature. It is shown from the measurement of helium or oxygen gas diffusion in the gels that the gas diffusion is limited by the average pore diameter of the gel, R_a; that is, the mean free path of gas in a porous gel can be regarded as equal to R_a. The results also indicate that the gas diffusing length is about three times larger than the geometrical thickness of the sample gel. Some adsorption of oxygen gas appears to take place on the silica surface of the gel at room temperature.     

Growth of Te(OH)6Na2HPO4 · H2O single crystals in silica gel and their characterization

Single crystals of Te(OH)₆Na₂HPO₄ · H₂O were grown in silica gel medium using single-test tube diffusion method. Hexagonal pyramidal and hexagonal tabular single crystals were obtained. Crystals were characterized by IR, X-ray, and Raman studies.     

Growth of manganese tartrate trihydrate in silica gel

Growth of manganese tartrate trihydrate crystals in silica gel media with manganese chloride and manganese sulphate as the reactant is attempted. The reason for the occurrence of platelets along with dendrites in the case of manganese sulphate is discussed. IR, X-ray, atomic absorption and thermogravimetric techniques are employed to characterize the grown crystals and the results are discussed.