Calorimetric determination of the enthalpy of formation of InN and comparison with AlN and GaN

The standard enthalpy of formation of InN at 298 K has been determined usin g high-temperature oxidative drop solution calorimetry in a molten sodium m olybdate solvent at 975 K. Calorimetric measurements were performed on six InN samples with varying nitrogen contents. The samples were characterized using x-ray diffraction, chemical analysis, electron microprobe analysis, a nd Brunauer-Emmett-Teller surface area measurement. The variation of the en thalpy of drop solution (kJ/g) with nitrogen content is approximately linea r. The data, when extrapolated to stoichiometric InN, yield a standard enth alpy of formation from the elements of -28.6 +/- 9.2 kJ/mol. The relatively large error results from the deviation of individual points from the strai ght line rather than uncertainties in each set of data for a given sample. This new directly measured enthalpy of formation is in good agreement with the old combustion calorimetric result by Hahn and Juza (1940). However, th is calorimetric enthalpy of formation is significantly different from the e nthalpy of formation values derived from the temperature dependence of the apparent decomposition pressure of nitrogen over InN. A literature survey o f the enthalpies of formation of III-N nitride compounds is presented.