Competitive formation of intermetallic phases in Y0.7(Nb,Ti)0.3Co2 system: Experiment and thermodynamic modeling

Process of crystallization of Nb and Ti substituted compounds was analyzed using x-ray diffraction and semi-empirical modeling. Different crystallization products were observed for Y0.7Nb0.3Co2 and Y0.7Ti0.3Co2 despite similar electronegativities and atomic radii of niobium and titanium. Calculations using Miedema's model confirmed the stability of intermetallic compounds in the broad range of compositions at the expense of solid solution and amorphous phase. While in Y0.9(Nb, Ti)0.1Co2 single C15 Laves phase is forming, two phases (YCo2 and NbCo2) are crystallizing in Y0.7Nb0.3Co2. In the case of Ti-substituted sample, three phases with different Ti content were observed due to similar formation enthalpies of intermetallic compounds in analyzed range of compositions (−33.7 and −32.1 kJ/mol for Y0.9Ti0.1Co2 and Y0.7Ti0.3Co2, respectively).