Structural phase transition and internal fields in rubidium thiocyanate probed through vibrational spectroscopy |
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Authors: | S Sathaiah H D Bist |
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Institution: | (1) Department of Physics and Centre for Laser Technology, Indian Institute of Technology, Kanpur, India |
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Abstract: | A comprehensive vibrational study of Rubidium thiocyanate (RbNCS), in the 298–448°K range reveals that the orthorhombic to tetragonal transition atT
c440°K is of order-disorder type exhibiting purely second order characteristics. A consistent order-parameter exponent 0.45±0.04 has been obtained from both Raman and IR measurements. In the Raman spectra, the appearance of sidebands in both the C–N&C–S stretching modes and their temperature dependence indicate the existence and a gradual diminution of internal electric field asT approachesT
c. These results have been discussed in the context of an anharmonic oscillator model. An activation energy (U) for the reorientational motion of NCS– ions,U0.29±0.02 eV, has been calculated from large changes in the bandwidth (C-N) nearT
c. |
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