• P Ganguly

      Articles written in Bulletin of Materials Science

    • Itinerant electron behaviour and long-range ordering in La1−xSrxCoO3

      P Ganguly W H Madhusudan

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      Electrical resistivity of La1−xSrxCoO3 is reduced significantly by the substitution of Ni3+ ions in place of the cobalt ions. In the La1−xSrxCo1−yNiyO3 system, for small values ofx(x=0·05) superparamagnetic clusters seem to be formed at lower temperatures (<300 K). The formation of such clusters is not affected by the presence of nickel ions. Whenx is large, the occurrence of long-range ordering seems to depend on the itinerancy of charge carriers.

    • Systematics in the electron transport and magnetic properties of LnBO3 perovskites

      P Ganguly C N R Rao

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      Systematics in the electrical and magnetic properties of transition metal perovskites LnBO3 (Ln=rare-earth ion, B=3d transition metal) with the variation of Ln and B ions are reviewed. The electrical resistivity and activation energy of LnBO3 compounds increase with the decreasing size of the Ln3+ ion for a given B ion. The low-spin to high-spin transition temperature of Co3+ ion in LnCoO3 similarly increases with the decrease in size of Ln3+ while the magnetic ordering temperatures in LnVO3, LnFeO3, LnCrO3 and LnSrCo2O6 decreases with decreasing size of the rare-earth ion. These results may be understood in terms of the increasing acidity of the rare earth ion with decreasing size and the competition between the Ln3+ and the B3+ ions for covalency with the oxygen ions. The effect of this competition on the metal oxygen covalency and crystal field parameter is discussed in relation to the results obtained and Goodenough’s phase diagram. The possibility ofd-f exchange interaction in La1−xLnx NiO3 is also discussed in the light of ESR results.

    • Low-temperature preparation of some perovskites La2MM′O6 (M, M′=Cr, Mn, Fe, Co, Ni, M≠M)

      P Ganguly

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      The low-temperature preparation of some La2MM′O6 compounds (M,M′=Cr, Mn, Fe, Co, Ni, M≠M′) by the decomposition of coprecipitated basic carbonates is described. Single phase compounds are formed. The stability of physical properties of these phases towards further heating depends on the M and M′ ions. The results are interpreted in terms of the stability of the M-M′ oxidation states.

    • Crystal growth from melt in space

      P Ganguly

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      A review of experiments on crystal growth from melt in nearly zero gravity environments in space is given. The review includes experiments from skylab and ASTP missions. The results discussed are morphological observations, melt interfaee observations, dopant segregation, alloy solidification and containerless experiments.

    • Near-neighbour impurity effect on the spin-state transitions in LaCoO3 at low temperature (12<T<300 K)

      N Y Vasanthacharya P Ganguly

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      The low-temperature magnetic susceptibility behaviour of LaCoO3 prepared under different conditions as well as substituted samples such as LaCo0.95M0.05O3 (M=Al, Ga, Cr, Fe, Mn, Ni) and La0.98Sr0.02CoO3 have been investigated in the temperature range 12–300 K. Earlier interpretations of the magnetic susceptibility have been reexamined. In the case of LaCoO3 samples containing Al, Ga, Cr and Fe impurities spin-state transitions involving a temperature independent activation energy (∼0.01 eV) are observed atT<200 K. Analysis of the data indicates that either the excited state has an intermediate-spin (t2g5eg1) configuration or only half the Co ions are involved in the activated transition to the high-spin (t2g4eg2) configuration. Al3+, and Cr3+ increases the activation energy considerably. Substitution of L ≠ 0 ions such as Mn3+ and Ni3+ or Co4+ (low-spin) seems to introduce ferromagnetic interactions and stabilizes the paramagnetic state. LaCoO3, when Co is substituted by Mn (5%) or La is substituted by Sr (2%) show giant magnetic moments. When Co is substituted by Ni (5%) a ferromagnetic ground state is observed.

    • In situ photoacoustic spectroscopic studies on heterogeneous catalysts under conditions of gas flow

      T Somasundaram P Ganguly

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      An all-glass open photoacoustic cell through which gases can be passed without affecting the signal has been described. The cell has been characterized for various chopping frequencies and temperatures. Several heterogeneous catalytic reactions have been studied under conditions of gas flow at elevated temperatures and the potential application of this method in the field of heterogeneous catalysis has been pointed out.

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