Enthalpy of Formation of Gallium Nitride

Abstract

A major discrepancy in the literature concerning the enthalpy of formation of GaN has been resolved using oxidative oxide melt solution calorimetry. Four samples of differing nitrogen contents were measured by dropping them into molten 3Na 2 O‚4MoO 3 in a calorimeter at 975 K with oxygen gas bubbling through the solvent. The samples were characterized by X-ray diffraction, chemical analysis, transmission electron microscopy, particle size analysis, and BET measurements. The enthalpy of drop solution (kJ/g) varied approximately linearly with nitrogen content. Extrapolated to stoichiometric GaN, the data yield a value of -156.8 ( 16.0 kJ/mol for the standard enthalpy of formation from the elements at 298 K. The relatively large error reflects the deviation of individual points from the straight line rather than uncertainties in each set of data for a given sample. This new directly measured enthalpy of formation is in excellent agreement with that obtained from the temperature dependence of the equilibrium pressure of nitrogen over GaN, -157.7 kJ/mol, measured by Madar et al.

Calculation of the thermodynamic properties of AIII nitrides

“…High-temperature oxidative solution calorimetry was used recently [13] to determine the heat of formation of solid GaN. The value À156.8716.0 kJ mol À1 is in very good agreement with the data derived from high-pressure equilibrium measurements: À157.7 kJ mol À1 [14,15] (without any correction due to differences between the mean temperature of measurements and 298.15 K).…”

“…The resulting values fall into the experimental error bars of the calorimetric and equilibrium measurements-À312.273.3 kJ mol À1 for AlN [7][8][9], À156.8716 kJ mol À1 for GaN [13], and À71.078.0 kJ mol À1 for InN [6].…”

High-temperature oxide melt calorimetry of oxides and nitrides

“…This serves to control oxygen fugacity in the melt and, equally importantly, to stir the solvent effectively (and with no spurious calorimetric signals like those from mechanical stirring). Maintaining high oxygen fugacity by bubbling oxygen through the solvent also has led to success in an oxidative dissolution process for nitrides (12)(13)(14)(15)(16)(17)(18)(19)(20)(21) for Fe 2+ -bearing carbonates, (22,23) and for Ce 3+ -bearing oxides. (24) These improvements have dramatically extended the chemical variety of systems for which we can obtain reliable thermochemical data.…”

Final Report, "Thermochemical Studies of Nitrides, Oxynitride, and Oxide Ceramic Materials"

“…As part of Mandar Ranade's thesis, the hearts of formation of indium and gallium nitride, important materials in the semiconductor industry, were redetermined and serious discrepancies in the literature resolved (Ranade et al 2000. Iron nitrides (Tessier et al 2000b) and cerium manganese nitrides were also studied.…”