• K S Raju

      Articles written in Bulletin of Materials Science

    • Evidence of edge and screw dislocations in gypsum single crystals

      K S Raju

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      A row of closely packed equispaced etch pits are observed on etching (010) basal cleavages of gypsum with analar grade nitric acid and 0·1 N potassium hydroxide solution. It is established that these rows of pits are true to the whole bulk of the crystal, by successive etching and etching of match pairs, thin flakes as well as using different etchants. These rows of pits reveal low angle grain boundaries consisting of equispaced edge dislocations in the crystal. Irregular arrays of etch pits observed exactly correspond to its match face. Studying these rows on higher resolution, it is observed that they may reveal tilt or twist boundaries consisting of both edge and screw dislocations, probably created due to the impingement of the mis-oriented guest crystal causing stresses to the growing crystal. The implications are discussed.

    • Growth mechanism of Herring-Bone and Hour-glass synthetic gypsum

      D Jayakumar K S Raju

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      Synthetic gypsum crystals are grown from sodium meta silicate gel when 1M calcium chloride solution diffuses into the gel imbedded with 1M amonium sulphate solution. Acicular-shaped crystals of Herring-Bone structure are observed. When methanol was added to the gel medium, tabular crystals revealing Hour-glass structure are rarely observed. In the presence of methanol the silicate particles are inhibited from being incorporated into the crystals as a result of pushing and incorporating mechanisms. Inclusion of silicate particles in traces gives rise to Hour-glass pattern. The implications are discussed.

    • Evidence of screw dislocations on (002) cleavages of lithium carbonate single crystals

      K S Raju M Palaniswamy P Ramasamy G S Laddha

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      Well-defined triangular etch pits are produced on etching (002) cleavages of lithium carbonate single crystals with 2% citric acid. On etching of cleavage face and matched face these pits nucleate at the intersection sites of dislocations with the cleavage face. On successive etching of a cleavage face, shallow irregular arrays of pits do not enlarge in size as compared to other isolated pits on the same face. These irregular arrays of pits have reasonable correspondence on an etched match face, suggesting they form at dislocation sites.

    • Structural characterization of gel-grown neodymium copper oxalate single crystals

      K S Raju K N Krishna Jayakumari Issac M A Ittyachen

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      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 (3d5/2) and Cu (2p3/2) 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.

    • Praseodymium barium molybdate—its growth and structural characterization

      Jayakumari Isac M A Ittyachen K S Raju

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      Praseodymium barium molybdate (PBM) single crystals grown by gel method, reveal multiple and isolated octahedral bipyramidal crystals as well as spherulites of PBM at different depths from the surface inside the gel. Oscillation X-ray diffraction pattern of the sample reveals that PBM is single crystalline in nature. Infrared absorption spectrum confirms the presence of molybdate (MoO4)2− ions in PBM, while the thermogravimetric analysis shows that PBM loses molybdenum oxide component around 420°C. Energy dispersive X-ray analysis establishes the presence of Pr, Ba and Mo in the sample. X-ray photoelectron spectroscopic studies of PBM establish the presence of Pr, Ba and Mo in their respective oxide states. An empirical structure has been proposed on the basis of these findings. The implications are discussed.

    • Some structural aspects of neodymium praseodymium oxalate single crystals grown in hydro silica gels

      Cyriac Joseph M A Ittyachen K S Raju

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      The mixed crystals of neodymium praseodymium oxalate are grown by the diffusion of a mixture of aqueous solutions of neodymium nitrate and praseodymium nitrate (as an upper reactant) into the set gel embedded with oxalic acid. By varying the concentration (by volume) of rare earth nitrates in the upper reactant, the incorporation of Nd and Pr in the mixed crystals has been studied. Tabular crystals with the well defined hexagonal basal planes are observed in the mixed crystals of varying concentrations. X-ray diffraction patterns of these powdered samples reveal that these mixed crystals are ‘isostructural’, while IR and FTIR spectra establish the presence of oxalate groups. TGA and DSC analyses show the correctness of the chemical formula for the mixed crystals, by the release of water molecules (endothermic) and of CO and CO2 (exothermic), with the rare earth oxides as the stable residue. X-ray fluorescence (XRF) and energy dispersive X-ray analyses (EDAX) establish the presence of heavy rare earth elements qualitatively and to a good extent quantitatively. X-ray photoelectron spectroscopic (XPS) studies confirm the presence of rare earth elements (Nd and Pr) as their respective oxides. The findings of these techniques of characterization are in excellent agreement with the proposed empirical structure for the mixed rare earth oxalates. The implications are discussed.

    • Lanthanum samarium oxalate — its growth and structural characterization

      Varughese John M A Ittyachen K S Raju

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      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.

    • Growth and physico chemical characterization of lanthanum neodymium oxalate single crystals

      K S Raju Varughese John M A Ittyachen

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      Single crystals of lanthanum neodymium oxalate (LNO) are grown in sodium meta silicate gels, by the diffusion of a mixture of aqueous solutions of lanthanum nitrate and neodymium nitrate into the test tube having the set gel containing oxalic acid. The bluish pink coloured tabular crystals of LNO having well defined hexagonal basal planes appear either as ‘foggy’ or ‘clear’, the latter at the greater depths inside the gel. The colouration of LNO visually observed is evidenced in UV-visible spectrum, by the revelation of well pronounced characteristic peaks in the visible region (500–900 nm). X-ray diffraction (XRD) of powdered LNO is ordered, meaning crystalline in nature, besides its ‘isostructurality’ with similarly grown lanthanum samarium oxalate crystals. The single crystallinity of LNO is established by its oscillation XRD pattern. Thermogravimetric analysis (TGA) and differential scanning colorimetry (DSC) support that LNO loses water of crystallization around 120°C and CO and CO2 around 350–450°C, while the infrared absorption (IR) spectrum of LNO establishes the presence of oxalate (C2O4)2− ions. Energy dispersive X-ray analysis (EDAX) confirms the presence of La and Nd in the sample. X-ray photoelectron spectroscopic (XPS) studies of LNO establish the presence of La and Nd in their respective oxide states. An empirical structure for LNO has been proposed on the basis of these findings. The ‘smokiness’ in the foggy LNO crystal has been attributed due to the ‘gel inclusion’ during the growth process.

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