Vaporization thermodynamics and heat capacities of Ti₅Ge₃ and Ti₆Ge₅

Thermodynamic stabilities of titanium germanides Ti₅Ge₃ and Ti₆Ge₅ have been studied by means of high-temperature Knudsen effusion mass spectrometry (KEMS) and differential scanning calorimetry (DSC). Thermodynamic activities of Ti and Ge have been measured over the two-phase mixtures of Ti₅Ge₃+Ti₆Ge₅ in a temperature range of ca. 1680-1880 K by direct comparison with solid Ti and liquid Ge metals. The standard free energies of formation of Ti₅Ge₃ and Ti₆Ge₅ at high temperature were determined from the activity data. Heat capacities of Ti₅Ge₃ and Ti₆Ge₅ were measured by DSC in the temperature region 300-700 K. Standard enthalpies of formation of Ti₅Ge₃ and Ti₆Ge₅ at 298 K were calculated by the third-law method with the use of estimated absolute entropy and high-temperature heat capacity data. The results obtained are: 1/8Ti₅Ge₃, -69.8±5 kJ; 1/11Ti₆Ge₅, -70.1±5 kJ. The results obtained in this work are compared with previous estimates and measurements.