Thermal Correction Of The General Equation Of State For Si <sub> 3 </ Sub> N <sub> 4 </ Sub> Nature

The Einstein model to consider thermal effect in universal equations of state (UEOS) is modified. It is proposed that the zero-point vibration term should be deleted in a thermal UEOS, and the parameters can not be directly taken as experimental data at a reference temperature, V_R , B_R , B'_R andγ_R^G, but their values at absolute zero temperature, V₀ , B₀ , B'₀ andγ₀^G. An approach is proposed to solve V₀ , B₀ , B'₀ andγ₀^G from V_R , B_R , B'_R andγ_R^G. The approaches are applied to three typical universal EOSs, including the Baonza, mMNH and Vinet EOSs. The numerical results show that the solved values of parameters are almost identical for different EOSs. And the thermo-physical properties predicted through different EOSs are almost identical at zero and low-pressure conditions, once the same approach and input experimental data are used to solve parameters. It is concluded that the prediction of thermo-physical properties at zero and low-pressure conditions cannot be taken as the criteria to judge the applicability of a universal EOS.The thermal Baonza is applied to study thermo-physical properties ofα,βandγ-Si3N4. Through analyzing experimental data in literature, the input data-set for the three phases are determined. The results calculated from the thermal Baonza are in agreement with experimental data available.