Event calendar file
DCMPMS Seminars
Role of thermal vibrations in alloy and magnetic phase Transitions
by Prof. Prasanna T.R.S. (Dept of Metallurgical Engg. and Materials Science IIT Bombay),
Tuesday, September 27, 2011
from
to
(Asia/Kolkata)
at Colaba Campus ( AG-80 )
at Colaba Campus ( AG-80 )
| Description |
We address and resolve a fundamental contradiction that has existed from the earliest studies on phase transitions between theoretical models that ignore the role of thermal vibrations and analysis of diffraction data that always incorporates the role of thermal vibrations even though it is also possible to analyse the same data by ignoring thermal vibrations. All theoretical models are constrained by diffraction data to represent the interaction parameter or the exchange integral as temperature dependent, J(T). A new representation of the long range order parameter is proposed that fully represents its dependence on several key variables. In alloy phase transitions, the discrepancy between the experimental and theoretical ordering energies in Ni3V and Pd3V is direct evidence of their temperature dependence. Thermal vibrations influence order/disorder transitions through both the configurational and vibrational terms and not just the vibrational terms as hitherto believed. For magnetic phase transitions, the error due to neglect of thermal vibrations can be obtained from diffraction data. This error must be reported if the experimental order parameter is compared with that predicted from static lattice models. |
