Calculation of the Thermodynamic Quantities for Cubic Gauche Nitrogen (cg-N)

Abstract

This work aims to investigate the thermodynamic properties of the cubic gauge nitrogen (cg-N) by calculating the relevant thermodynamic quantities as a functions of temperature and pressure. The thermodynamic quantities of volume (V), thermal expansion (αp), isothermal compressibility (κT), bulk modulus(B), and the heat capacity (Cp) are calculated as a function of temperature at constants pressures (0, 35, 125, 250 GPa) for the cg-N structure. Also, the pressure dependences of V, κT, αp, Cp and γ (macroscopic Grüneisen parameter) are predicted at T= 295 K for this structure. This calculation is caried out by the thermodynamic relations using some literature data. From our calculations, we find that the κT, αp and also B exhibit anomalous behavior as the temperature lowers below about 100 K at constant pressures studied. This is an indication that cg-N transforms to a solid phase at low temperatures (below about 100 K). Experimental measurements can examine this prediction when available in the literature for the cg-N phase. Also, our predictions of the κT, αp, Cp and γ at various pressures (T= 295 K) can be examined experimentally for the cg-N phase. This calculation method can be applied to some other structures.