HEAT-CAPACITY OF MGSIN2 BETWEEN 8 AND 800 K

The specific heat at standard pressure (C(p)degrees) of MgSiN2 was det ermined by adiabatic calorimetry in the range of 8-400 K and different ial scanning calorimetry in the range of 300-800 K. The measured C(p)d egrees data for T < 24 K can be described using the Debye T-3 approxim ation: C(p)degrees = aT(3) with a = 1.3632 x 10(-5) J mol(-1) K-4. For temperatures between 350 and 650 K the C(p)degrees can be described w ith the Debye equation using a constant Debye temperature of 996 K. Fo r temperatures between 24 and 350 K the Debye temperature is a functio n of temperature and has a minimum value of 740 K at about 55 K. The C (p)degrees data for T greater than or equal to 300 K were compared wit h those of AlN. As expected, the C(p)degrees data of MgSiN2 were about a factor 2 larger than those of AlN. The entropy S(T)degrees, the ent halpy (H(T)degrees - H(O)degrees), and the energy function (G(T)degree s - H(O)degrees) in the range of 0-800 K were calculated using standar d thermodynamic formulas. By extrapolating the C(p)degrees data to hig h temperatures at which G(T)degrees is known, H(O)degrees was estimate d to equal -534 kJ mol(-1).