HEAT-CAPACITY MEASUREMENTS OF MG-Y-SI-AL-O-N GLASSES

Heat capacity measurements on two glasses in the Mg-Y-Si-Al-O-N system have been carried out by differential thermal analysis in the range f rom room to the glass transition temperatures. The substitution of oxy gen by nitrogen in the anionic network, the cationic one remaining the same, leads to an increase in the solid heat capacity measured at a c onstant pressure, over the whole range of temperature. Furthermore, th e difference between the C-p of the solid state and the liquid state i s close to 10 kJ per mole in the two glasses. The determination of the Debye temperature gives 930 K for the oxide glass and 952 K for the o xynitride one, the corresponding Debye frequencies being 647 and 663 c m(-1), respectively. Moreover, we determined the activation energies f or relaxation of these glasses: 836 and 962 kJ/mol for the oxide glass and the oxynitride glass, respectively. (C) 1998 Elsevier Science B.V . All rights reserved.