Pure and Applied Chemistry

Abstract: The defect chemistry of different ordered intermetallic compounds with the A₃B stoichiometry was investigated. Three groups were distinguished according to their crystal structure: L1₂ compounds (Ni₃Al, Ni₃Ga, Pt₃Ga, Pt₃In), D0₁₉ compounds (Ti₃Al), and D0₃ compounds (Fe₃Al, Ni₃Sb). Statistical-thermodynamic models were derived based on a Wagner-Schottky approach, and the calculated activity curves (thermodynamic activity vs. composition) were compared with experimental activity data. In this way, we attempted to obtain at least estimated values for the energies of formation of the different types of point defects present in the corresponding compound, both as configurational defects (which are responsible for nonstoichiometry) and as thermal defects. In the majority of cases, thermodynamic activities had to be determined experimentally in the present study, using either an emf method with a solid electrolyte (Ni₃Ga, Pt₃Ga, Pt₃In, Fe₃Al) or a Knudsen cell-mass spectrometric method (Ni₃Sb).