Critical values for specific heat from Raman data

Abstract

Abstract The use of Raman frequency shifts of non-soft modes to provide detailed predictions of the critical behaviour of specific heat up to within a fraction of a degree of a second order (or weakly first order) phase transition is illustrated. As an example, the λ-transition of ammonium chloride under ambient pressure has been studied, and values of critical exponents of a − ≈0.76 and a + ≈0.82 have been derived for C p , from the Raman data. This approach is believed to be valid for a wide range of systems showing second-order or weakly first-order phase transitions and it is possible to use it for relatively inaccessible samples such as those within high pressure enclosures.