• S Radhakrishna

      Articles written in Proceedings – Section A

    • A method of deriving shubnikov groups

      P V Pantulu S Radhakrishna

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      The 122 Shubnikov groups are derived directly starting from the 11 pure rotation groups and simultaneously introducing two anti-identity operations.

    • Trapped point defects in crystals: Simultaneous occurrence of two vacancies

      P V Pantulu S Radhakrishna

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      Group theoretical methods have been used for obtaining the relaxation modes and relaxation times for the case of two vacancies simultaneously occurring when a crystal with CsCl structure has a trivalent impurity like Pr3+ introduced substitutionally.

    • Piezoelectric relaxation in crystals containing point defects

      S Bhagavantam S Radhakrishna

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      The phenomenon of piezoelectric relaxation in crystals has been dealt with briefly by applying group theoretical methods. Three typical crystal classes which are capable of exhibiting piezoelectricity are considered in some detail and a study is presented of the possible piezoelectric relaxation when different defect complexes are introduced in the crystals. The concept of an anisotropy in piezoelectric relaxation has been brought out in a crystal class belonging to the orthorhombic system.

    • Raman spectra of irradiated NaClO3 and KClO3 crystals

      S Radhakrishna A M Karguppikar

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      Pure undamaged NaClO3 and KClO3 crystals show four Raman lines arising from the internal oscillations in the ClO3 ion, besides a few other Raman lines due to lattice oscillations. On radiation damage by X-rays or γ-rays some new lines are observed in each crystal. In particular, two lines at ∼ 680 and ∼ 930 are assigned to the ozonide ion (O3) in these lattices. It is postulated that by radiation damage a certain number of ClO3 ions, which initially have a pyramidal structure, loose the chlorine atom leaving the three oxygen atoms at the corners of an equilateral tri-angle. Since an equilateral triangular structure should exhibit two normal oscillations, both of which are Raman active, such a postulate satisfactorily explains experimental results.

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