Issue no. 27 3 O c t o b e r 2006 88 MODELING OF ANOMALOUS THERMODYNAMIC PROPERTIES USING LATTICE DYNAMICS AND INELASTIC NEUTRON SCATTERING R. Mittal Solid State Physics Division Bhabha Atomic Research Centre A b s t r a c t This paper summarizes the recent developments of the modeling of anomalous thermodynamic properties. It has been shown that lattice dynamics calculations along with inelastic neutron scattering measurements can be employed to reveal phonon properties and to predict thermodynamic properties of various compounds including materials with negative thermal expansion. There is a large variation in the thermal expansion, specific heat and equation of state pertaining to the compounds described in this paper. The interatomic potentials as determined for various compounds have been able to successfully model the thermodynamic behaviour. The variations in phonon spectra manifest in the thermodynamic properties of various compounds at high pressure and temperature. The author has received the “Golden Jubliee Young Achiever Award” during the DAE-Solid State Physics Symposium held at BARC, Mumbai, India, during December 5-9, 2005. Introduction The study of lattice vibrations is of considerable interest because several physical properties of crystals like specific heat, thermal expansion, thermal conductivity and phase transitions are related to the vibrations of atoms in solids [1-4]. We have developed models of interatomic potentials for several compounds of interest, which allow to calculate the structural and dynamical properties as a function of pressure and temperature. The data obtained from neutron scattering and optical experiments are used to test and validate models of interatomic potentials [1,2]. The models are then used for calculating various thermodynamic properties at high pressures and temperatures. We are able to provide the predictions of equation of state, specific heat and thermal expansion. A brief description of the scientific interest and results obtained for various compounds are given below. Results and discussion The compounds ZrW 2 O 8 , HfW 2 O 8 and ZrMo 2 O 8 are of considerable interest [5] due to their large