Oxalate Single Crystals Research Articles

EPR and optical absorption studies of vanadyl impurity in lithium hydrogen oxalate single crystal

Electron paramagnetic resonance (EPR) and optical absorption studies of vanadyl ions in lithium hydrogen oxalate monohydrate single crystal and powder are reported at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes, a b ∗ , b ∗ c ∗ and a c ∗ indicate four different vanadyl complexes. The detailed investigation of EPR spectra indicates that one of the VO 2 + sites (the intense one) may enter the lattice substitutionally and the other three occupy the interstitial positions. From the angular variation, the spin Hamiltonian parameters are evaluated and discussed. The optical absorption spectrum shows four bands. From the optical and EPR data, various bonding parameters are determined and the nature of bonding in the crystal is discussed.

Diamagnetic and photoabsorption characterisation of gel‐grown cadmium oxalate single crystals

AbstractPerfect single crystals of cadmium oxalate trihydrate have been grown using the slow and controlled reaction between Cd+2 and (C2O4)‐2 ions in agar‐agar gel, resulting in the formation of insoluble product Cd(COO)2.3H2O. The optimum growth parameters have been determined. The variation of magnetic moment of the grown crystals under an applied static magnetic field is studied and the material is found to be diamagnetic. The polarizability is found sensitive to optical band gap. An empirical relation between magnetic susceptibility and electronic polarizability has been established. Optical absorption spectra of the sample recorded in the range 200‐2500 nm reveal transitions involving absorption and emission of phonons. The detailed study supports the existence of allowed direct and indirect allowed gaps in the material. The direct allowed transition prevails in the region of relatively higher photon energy. Some feeble disorder in the crystal is conceived to be present. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal structure and thermal characterization of cadmium oxalate [CdC 2O 4 · 3H 2O] and barium-doped cadmium oxalate [Ba 0.5Cd 0.5(C 2O 4) 2 · 5H 2O] single crystals grown in silica gel

Pure cadmium oxalate trihydrate (COT) and barium added cadmium oxalate (BCO) single crystals were grown by controlled diffusion of Cd 2+ and Ba 2+ ions in silica gel at ambient temperature. A single test tube technique coupled with gel aging conferred maximum size crystals by controlling the nucleation rate. It was found that the pH and age of the gel greatly influenced the crystal quality, their size and transparency. Grown crystals CdC 2O 4 · 3H 2O and Ba 0.5Cd 0.5(C 2O 4) 2 · 5H 2O were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and thermal analysis. Effect of barium dopant on the growth and morphology of cadmium oxalate was studied. Pure cadmium oxalate crystallized in triclinic system and the barium-doped cadmium oxalate crystallized in hexagonal system with massive changes in their unit cell parameters. The infrared spectrum revealed the presence of oxalate ligands and water of hydration in both the pure and barium-doped crystals. Thermal analysis showed that the grown crystals were dehydrated thermally even from lower temperatures and the doped crystals were found more stable.

Thermal, FT-IR and dielectric studies of gel grown sodium oxalate single crystals

Oxalic acid metabolism is important in humans, animals and plants. The effect of oxalic acid sodium salt is widely studied in living body. The growth of sodium oxalate single crystals by gel growth is reported, which can be used to mimic the growth of crystals in vivo. The grown single crystals are colourless, transparent and prismatic. The crystals have been characterized by thermogravimetric analysis, FT-IR spectroscopy and dielectric response at various frequencies of applied field. The crystals become anhydrous at 129·3°C. Coats and Redfern relation is applied to evaluate the kinetic and thermodynamic parameters of dehydration. The dielectric study suggests very less variation of dielectric constant with frequency of applied field in the range of 1 kHz-1 MHz. The nature of variation of imaginary part of complex permittivity, dielectric loss and a.c. resistivity with applied frequency has been reported.

Growth and characterization of glycinium oxalate (GOX) single crystals

Glycinium oxalate (GOX) single crystals were grown by slow cooling solution growth method. The X-ray diffraction and Fourier transform infra red studies confirm the grown crystal. The hardness values of GOX are found to be higher than glycine. The increase in hardness may be due to the C–H---O bonding. The UV–Visible studies show that GOX crystals can be used for nonlinear applications. The dielectric measurement indicates that the GOX crystals have domains of varying sizes and varying relaxation time. The SHG output of GOX was 210 mV at given pulse energy of 5 mJ/s and KDP was 240 mV.

Optimized growth and characterization of cadmium oxalate single crystals in silica gel

Single crystals of cadmium oxalate hydrate have been grown in silica gel in the presence of divalent Cd 2+ ions impregnated with oxalic acid at room temperature. Gel aging technique was adopted to reduce the nucleation density and hence larger and more perfect single crystals were harvested. Obtained crystals exhibit triclinic structure with unit cell dimensions a = 6.0059 Å, b = 6.66 Å, c = 8.49 Å, α = 105.71°, β = 98.99° and γ = 74.66°. IR spectrum indicates the presence of oxalate ligands and water of crystallization. Thermal behavior and stability of the grown cadmium oxalate crystals were investigated in the temperature range of 30–600 °C. A.C. electrical conductivity of Cd(C 2O 4)·3H 2O was measured for different frequencies and was found to lie between usual conductivities of semiconductor and insulator. The activation energy required to move permanent intrinsic defects in the crystal lattice was found and was equal to 0.15 eV.

Growth and study of barium oxalate single crystals in agar gel

Barium oxalate was grown in agar gel at ambient temperature. The effect of various parameters like gel concentration, gel setting time and concentration of the reactants on the growth of these crystals was studied. Prismatic platy shaped spherulites and dendrites were obtained. The grown crystals were characterized by X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis. An attempt is made to explain the spherulitic growth mechanism.

Studies on the growth and optical characterization of dysprosium gadolinium oxalate single crystals

AbstractPreparation and optical characterization of dysprosium gadolinium oxalate (DGO) single crystal is reported. The crystals were grown using silica gel technique, by the controlled reaction of rare earth nitrates with oxalic acid. Crystals were characterized using X‐ray powder diffraction, optical absorption and fluorescence studies. Radiative transition probability, fluorescence branching ratio and radiative lifetime of Dy3+ in the crystal are evaluated by the parameterization of the absorption spectrum by the Judd‐Ofelt theory. The recorded fluorescence spectrum showed two well resolved peaks at 480 nm and 571 nm and are assigned to the transitions from 4F9/2 → 6H15/2 and 6H13/2 of Dy3+. Stimulated emission crossection and optical gain of these transitions are also evaluated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of temperature on nucleation and growth of cadmium oxalate single crystals in silica gels

In continuation of our earlier work on the gel growth of single crystals, this paper presents results on the effect of temperature on nucleation and growth of cadmium oxalate single crystals. It has been found that the nucleation centres decrease drastically (to as low as two) as the temperature increases. Low nucleation centres resulted in larger and more perfect single crystals. The decrease in nucleation centres at higher temperature has been interpreted in terms of a decrease in supersaturation, an increase in critical size of nucleus and free energy of nucleus formation. The growth rates of the crystals measured as a function of temperature has clearly indicated that the crystal growth process in gel is a one-dimensional diffusion controlled process.

Lanthanum samarium oxalate — its growth and structural characterization

Lanthanum samarium oxalate (LSO) single crystals are grown in silica gels by the diffusion of a mixture of aqueous solutions of lanthanum nitrate and samarium nitrate into the test tube having the set gel impregnated with oxalic acid. Tabular crystals of LSO having well defined hexagonal basal planes are observed at different depths inside the gel. LSO crystals grown by this method are colourless and transparent. Laue transmission X-ray diffraction pattern of LSO reveals well defined spots with two-fold symmetry along the horizontal axis. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) support that LSO loses water around 120°C, and CO and CO2 around 350–450°C. The infrared (IR) absorption spectrum of LSO establishes the presence of oxalate (C2 O4)2− ions. Energy dispersive X-ray analysis (EDAX) confirms the presence of La and Sm in the sample. X-ray photoelectron spectroscopic (XPS) studies of LSO confirm the presence of La and Sm in their respective oxide states. An empirical structure for LSO has been proposed on the basis of these findings.

Structural characterization of gel-grown neodymium copper oxalate single crystals

Sparingly soluble neodymium copper oxalate (NCO) single crystals were grown by gel method, by the diffusion of a mixture of neodymium nitrate and cupric nitrate into the set gel containing oxalic acid. Tabular crystal, revealing well-defined dissolution figures has been recorded. X-ray diffraction studies of the powdered sample reveal that NCO is crystalline. Infrared absorption spectrum confirmed the formation of oxalato complex with water of crystallization, while energy dispersive X-ray analysis established the presence of neodymium dominant over copper in the sample. X-ray photoelectron spectroscopic studies established the presence of Nd and Cu in oxide states besides (C2O4)2− oxalate group. The intensities of Nd (3d 5/2) and Cu (2p 3/2) peaks measured in terms of maximum photoelectron count rates also revealed the presence of Nd in predominance. The inductively coupled plasma analysis supports the EDAX and XPS data by the estimation of neodymium percentage by weight to that of copper present in the NCO sample. On the basis of these findings, an empirical structure for NCO has been proposed. The implications are discussed.

Studies on impurity incorporation in cadmium oxalate crystals grown by gel method

Aspects of gel growth of cadmium oxalate single crystals doped with monovalent (Li+, Na+, K+ and NH +4 ) and divalent (Ca2+, Co2+, Ni2+ and Zn2+) cation impurities are discussed. The growth experiments were carried out by single diffusion method. In this paper the effect of composition of the supernatant solution is considered. Rigorous characterization involves determination of composition of cations by employing atomic absorption spectrophotometer and of anions by titration method. The Pauling radius, hydration energy and distribution coefficient of the cations are tabulated and the results are described and discussed.

Nucleation and growth of CdC2O4·3H2O single crystals in silica gels

As part of our work on growth of cadmium oxalate single crystals in gels, we describe here variation of nucleation density and growth of these crystals as a function of concentration of feed solution, gel ageing, gel density, gel pH and intermediate neutral gel column. While high density and high pH gels have been found to produce opaque crystals, good quality transparent single crystals have been obtained in low density and low pH gels. It was observed that the intermediate neutral gel column and gel ageing considerably reduced the number of nucleation sites and increased the size of the crystals without affecting their quality. By concentration programming the size of the crystals increased.

Electron spin resonance and proton ENDOR studies in potassium hydrogen oxalate single crystals

Radicals trapped in a γ-irradiated single crystal of potassium hydrogen oxalate have been investigated using ESR and ENDOR techniques. The CO–2 radical produced exhibited hyperfine interaction with nearby protons, and detailed ENDOR study revealed that one of these protons was partially transferred onto the radical site along the hydrogen bridge. Theoretical interpretation of the dipolar couplings indicate that the shift form the crystallographic position of this proton is small. A second species was observed and tentatively assigned to a protonated anion radical. These findings are discussed in relation to the anomalous couplings observed in sodium hydrogen oxalate monohydrate.

High resolution 14N NMR in solids: Single crystals of ammonium hydrogen oxalate hemihydrate

Proton decoupled 14N NMR spectra of ammonium hydrogen oxalate (AHOX) single crystals have been employed to determine the electric field gradient tensor at the 14N sites. Despite the 99.4% abundance of 14N, the spectral lines are narrow (∼300 Hz) and show two inequivalent 14NH4+ ions with (e2qQ/h) =130 kHz, η=0.39 and (e2qQ/h) =350 kHz, η=0.27. On the basis of motional averaging arguments, we surmise that these nonvanishing field gradients arise primarily because of lattice distortions of the N–H distances. The results indicate that it should be relatively easy to obtain 14N spectra in single crystals, and thus to examine a number of phenomena which have heretofore been inaccessible.

Hydrazine Cation Radical Formation in γ-Irradiated Single Crystals of Hydrazinium Hydrogen Oxalate

Room-temperature γ irradiation of hydrazinium hydrogen oxalate single crystals yields the hydrazine positive ion, which has been studied by electron spin resonance. The complex is planar, symmetry D2h, with the unpaired electron delocalized over the two nitrogen nuclei, which have the axial hyperfine coupling tensor AN = (2.5, 2.5, 27.6)G, aN = 11.0 G. The principal components of the proton coupling tensors are AH = (+2, −20.6, −13.0)G, aH = −10.4 G. The relative signs of the latter principal elements have been ascertained by comparing experimental and calculated spectra, for orientations of the crystal where ΔMI = 1 transitions are observed. The radical has a different orientation in the crystal compared with that of the parent ion. The reorientation is thought to be due to the influence of the hydrogen bonds between the hydrazine positive ions and neighboring oxygen atoms.