Thermochemistry of phosphorus oxynitrides: PON and LiNaPON glasses

High-temperature solution calorimetry has been very useful in elucidating t he energetics of many oxide materials. Recently, a sodium molybdate melt, 3 Na(2)0.4MoO(3), has been shown to be very effective for nitride calorimetry . This methodology has now been used to determine the energetics of formati on of phosphorus oxynitride PON samples and of a series of LiNaPON oxynitri de glasses. Enthalpies of formation from the elements at 298 K are --371.71 +/- 4.45 and -356.14 +/- 3.98 kJ mol(-1) for beta-cristobalite and amorpho us PON, respectively, and -961.88 +/- 3.86 kJ mol-l for a 9 wt % nitrogen-c ontaining LiNaPON glass. The P-cristobalite energy of amorphization is -15. 57 +/- 5.97 kJ mol(-1). A linear relation, Delta H-f(0)(Li0.5PO(3-3x/2)Nx) = Delta H-f(0)(Li0.5Na0.5PO3) + 441.7x, was found between the enthalpies of formation of the glasses and their atomic nitrogen content, x (0 less than or equal to x less than or equal to 0.57). The magnitude of the energetics of nitrogen/oxygen substitution within PON and LiNaPON glasses has been co rrectly evaluated by using N-N, O-O, P-N, and P-O bond strengths. The in-si tu precipitation of metallic particles from corresponding oxides in LiNaPON glasses has been predicted from high-temperature solution calorimetry resu lts and appropriate thermodynamic cycles. These results constitute the firs t set of energetic data on nitridophosphates.