• Bipin K Srivastava

      Articles written in Pramana – Journal of Physics

    • Infrared spectra of BeSO4.4H2O and its deuterated analogue in 4000–1200 cm−1 region

      Bipin K Srivastava D P Khandelwal H D Bist

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      IR spectra of BeSO4.4H2O and its deuterated analogue at ∼300 K and ∼110 K are reported in the region 4000–1200 cm−1 using thin film and nujol mull techniques. The observed bands have been assigned as the internal modes of the water and the overtones and combinations of various modes using the recently revised assignments of SO42− and Be(aq)4 fundamentals in the region 1200–250 cm−1 (Srivastavaet al 1976). The splitting of the internal modes of water has been discussed in the light of the effects of deuteration and cooling and it is shown that all the water molecules in a unit cell are asymmetric but crystallographically equivalent.

    • Infrared spectra of BeSO4.4H2O and its deuterated analogue at 110K in 1200–250 cm−1 region

      Bipin K Srivastava D P Khandelwal H D Bist

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      IR absorption spectra of BeSO4.4H2O and its deuterated analogue are reported in the region 1200–250 cm−1 at 110 K. The half-widths and relative integrated intensities of the bands are also reported. The study largely confirms the assignments for thev3 andv4 modes of SO42− ion and thev3 mode of Be(aq)42+, complex as made by Diemet al. The assignments of the other modes of SO42− and Be(aq)42+, and the librational modes of water are given a more solid footing as result of the present investigation.

    • Lattice sum calculations and a Mössbauer study on electric field gradient in phlogopite

      Anjali Krishnamurthy Bipin K Srivastava S Lokanathan

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      Lattice sum contributions have been calculated at the two octahedral sites in a phlogopite mica assuming a systematic distribution of octahedral cationic charges. This, unlike the case of a random distribution of charges, is able to reproduce broad features of quadrupole doublet spectra in Mössbauer experiments suggesting that the doublet assignments in terms of the two structural sites,M1 (trans) andM2(cis), are quite valid. Angle dependence of Mössbauer spectra has also been studied for a ferric-rich phlogopite mica sheet to determine the orientation of the EFG principal axis component and the sign of the quadrupole coupling constant. Quadrupole splitting values and the positive sign of coupling constants match the theoretical predictions quite well but the model fails to predict the observed EFG orientation.

    • On preparation of fine particles of MnFe2O4 and their magnetic properties

      S N Dolia Anjali Krishnamurthy Bipin K Srivastava Vipasha Ghose

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      Influence of the heat treatment, following a wet chemical process, has been examined on the sizes of the obtained particles of MnFe2O4. X-ray diffraction, magnetization and Mössbauer measurements have been used. The average sizes of the obtained particles are in the range of ∼ 100 Å–300Å with the upper size limit being ∼ 450 Å and more. The average size as well as size distribution is strongly influenced by the nature of the heat treatment followed for preparation of the sample. Prolonged hydrothermal heating resulted in larger average size than did dry heating at 400°C of the precipitate obtained from the initial wet process. Further dry heating following hydrothermal treatment did not lead to any major growth. Chemical nature of the starting materials also affects the sizes.

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