The project is aimed at experimental investigation of phonon density of states (PDOS) in cementite (Fe3C) at different temperatures using Inelastic Neutron Scattering (INS). The data obtained in our work will be used to calculate the carbon equilibrium stable isotope fractionation factor (so-called beta-factor) for Fe3C. The results are crucially important for understanding carbon behaviour and isotopic fractionation in deep Earth. Knowledge of the PDOS allows to calculate the phonon contribution into thermal thermodynamic properties of cementite and to find magnetic contribution into thermodynamic quantities such as heat capacity from comparison with appropriate calorimetry measurements. The PDOS obtained at different temperatures will allow us to estimate the anharmonic correction on thermodynamic properties of cementite (including the isotope factor).