• R G Maines

      Articles written in Pramana – Journal of Physics

    • Effect of high pressure on the vibrational modes and the energy gap of ZnP2

      A Jayaraman R G Maines T Chattopadhyay

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      The pressure dependence of the vibrational modes in ZnP2 has been investigated by Raman Spectroscopy using a diamond anvil cell, up to 150 kbar pressure. The intrachain phosphorus modes exhibit a strong pressure dependence whereas the low frequency Zn-P modes soften very slightly under pressure. For a crystal which is treated as a molecular crystal this is an unexpected result. It is suggested that the behaviour may be due to a buckling of the phosphorus chain, or due to a double bond promotion between P atoms, or a charge transfer under pressure. The shift in the energy gap has also been measured to 100 kbar hydrostatic pressure. There is a small initial blue shift which gradually changes over to a red shift. However the whole shift in 100 kbar is quite small. Combining the (dEg/dP)T with the published (dEg/dT)P the thermal expansion contribution and the electron-phonon interaction contribution were evaluated. The latter dominates the total (dEg/dT)P of ZnP2.

    • Pressure-induced structural transitions in PbI2: A high-pressure Raman and optical absorption study

      A Jayaraman R G Maines T Chattopadhyay

      More Details Abstract Fulltext PDF

      The effect of pressure on the 2H and 4H polytype of PbI2 has been investigated by Raman and optical absorption spectroscopy, using the diamond anvil cell. The 2H-polytype undergoes pressure-induced phase transitions at 5 kbar and near 30 kbar. The 4H-polytype exhibits phase transitions near 8 kbar and above 30 kbar. The Raman modes abruptly change at these pressures. The optical absorption edge shifts red at the rate of 15±1 MeV/kbar in the 2H-PbI2 and at the rate of 7 MeV/kbar in phase II. The latter phase is most likely to possess a 3d-structure and not a layer type. The possible structures for the high pressure phases are discussed.

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