P V Pantulu
Articles written in Proceedings – Section A
Volume 58 Issue 1 July 1963 pp 1-5
A new and elegant method, based on group theory, has been given for obtaining the maximum number of force constants needed in expressing the potential energy of a vibrating molecule characterised by a certain point group symmetry.
Volume 58 Issue 4 October 1963 pp 183-196
Group theoretical methods are developed for studying two types of point defects in crystals, namely trapped and untrapped ones, and the relaxation phenomena that arise therefrom. It is pointed out that a very close analogy exists between the relaxation modes on the one hand and normal oscillations on the other. This analogy enables us to utilise many of the concepts developed and the results obtained earlier in connection with studies on molecular spectra and Raman effect for an investigation of the relaxation phenomena. Simple rules are given for writing out the modes, ascertaining their activity or otherwise in regard to external electric and mechanical fields, evaluating the relaxation times and so on. Specific examples which are of practical interest are worked out under both the classes of defects studied. The methods developed can be applied to any general case.
Volume 59 Issue 1 January 1964 pp 1-13
Application of group theoretical methods to a study of the effect of symmetry on the physical properties of the 32 crystal classes as given earlier by Bhagavantam has been extended in this paper to a similar study of the magnetic properties of the 90 magnetic crystal classes. Results obtained in various cases agree with those derived earlier by more elaborate methods.
Volume 60 Issue 1 July 1964 pp 1-10
A group theoretical method given by one of us in earlier publications for studying the effect of crystal symmetry on physical properties is now extended to cover the galvanomagnetic, thermomagnetic and piezo-galvanomagnetic effects in single crystals. These effects have gained importance in semi-conductor physics and such studies are therefore of current interest and may be expected to yield valuable new information.
Volume 63 Issue 6 June 1966 pp 391-399
One-dimensional, two-dimensional and three-dimensional magnetic lattices have been derived making use of methods adopted by the authors in an earlier paper in deriving cystallographic magnetic point groups.
Volume 66 Issue 1 July 1967 pp 33-39
Neumann’s principle is examined in the context of the recent generalizations relating to symmetry and physical properties of crystals. It is shown that the difficulties encountered in applying the principle to transport properties are only apparent and that it is not necessary to impose restrictions on the principle. A proper interpretation of the symmetry of crystals resolves the difficulties and brings out clearly the axiomatic nature of this principle and its universal applicability.
Volume 66 Issue 2 August 1967 pp 107-111
The 122 Shubnikov groups are derived directly starting from the 11 pure rotation groups and simultaneously introducing two anti-identity operations.
Volume 67 Issue 2 February 1968 pp 109-114
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.
Volume 69 Issue 5 May 1969 pp 279-283
An alternative way of obtaining the generalized Onsager relations (Kleiner, 1966) which are valid for magnetic as well as non-magnetic crystals is given.