• O M Prakash

      Articles written in Pramana – Journal of Physics

    • Photoacoustic determination of energy band gap of semiconductors

      R S Ram O M Prakash A N Pandey

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      Semiconducting materials are employed in the fabrication of a number of semiconductor devices and opto-electronic detectors etc depending on their properties, state of purity and perfection and energy band gap values. In the present study, a latest and novel photoacoustic spectroscopic technique has been employed for the determination of energy band gap of some semiconductors namely CdS, CdSe, CdTe, ZnS, ZnO, Se and Si in the powder form. Values obtained have been compared with those reported by conventional methods.

    • Photoacoustic spectra of some laser dyes

      R S Ram O M Prakash

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      Photoacoustic spectra of rhodamine 110, rhodamine 6 G, rhodamine B, rhodamine 101 and coumarin 102 laser dyes have been recorded at room temperature of 25°C in the spectral range of 350–750 nm. These samples were taken in powder as well as in solution forms. For this purpose the closed and the open photoacoustic cells have been used. It is hoped the present study would be useful for characterization of these dyes.

    • Annealing, quenching and substitution effects on YBa2Cu3O7-δ: An XAS study

      P K Mehta S R Reddy O M Prakash B D Padalia

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      K-absorption edge region of copper in oxygen and air-annealed highTc(∼91 K) superconducting (SC) samples, YBa2Cu3O7-δ, has been investigated. The spectra exhibit a weak structure at ∼23 eV. To understand its origin, the spectra have been recorded for quenched Ce-substituted and semiconducting Y2BaCuO5 samples. It is argued that the weak structure (∼23 eV) is not a characteristic feature of an SC compound but appears to be a final state effect.

    • Thermal expansion of orthorhombic and tetragonal phases of the highTc superconductors RE1Ba2Cu3Oy (RE=Y, Gd, Dy)

      O M Prakash Ashok Rao O Prakash P N Dheer

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      Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases of RE1Ba2Cu3Oy(RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77–300 K. All the superconducting samples exhibit a jump Δα at their respective transition temperatures,Tc. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content.

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