The Macroscopic Atom Model (MAM) is extended with the halogens to obtain formation enthalpies and molar volumes of halides. Molar volumes and electron densities were obtained with ab initio methods assuming a hypothetical metallic state. The electronegativity parameter and transformation enthalpy were obtained by linear extrapolation and regression analysis. Negative transformation enthalpies were introduced to obtain reliable values for the formation enthalpy of halides. Formation enthalpies of halides are computed within 25 kJ/mol·at and their molar volumes are underestimated by 20%. The MAM provides better estimates than models using Pauling electronegativity or Born-Haber cycle calculations assuming an ionic lattice of the Born-Haber type. The inclusion of the halogens in the MAM scheme has extended its application to both alloys and ionic compounds. This model can now predict their formation enthalpies and molar volumes, which is not the case in all other electronegativity schemes.

Almost pure (Ti_1-xZr_x)₃SiC₂ MAX phase solid solutions with x ranging up to 0.17 were synthesized at temperatures in the range of 1450–1750 °C with reactive Spark Plasma Sintering (SPS). The zirconium partially replaces the M-element titanium of the Ti₃SiC₂ MAX phase up to x equals 0.17. The lattice parameters of the hexagonal (Ti_1-xZr_x)₃SiC₂ MAX phase are determined with X-ray diffraction using Rietveld refinement and show an anisotropic lattice expansion upon Zr insertion into Ti₃SiC₂. This observation is in very good agreement with density functional theory calculations where the deviation between the measured and calculated lattice parameter is less than 1%. The predicted elastic modulus reduction is only 4%. This behavior can be rationalized by considering the electronic structure, where only minute changes are observable as Zr is incorporated into Ti₃SiC₂. The measured nanohardness of the synthesized (Ti_1-xZr_x)₃SiC₂ MAX phase increases from 12.7 ± 1 GPa for Ti₃SiC₂ to 16.3 ± 1.1 GPa when x is raised from 0 to 0.17 due to an increasing amount of accompanying Ti_1-yZr_yC. The elastic moduli of (Ti_1-xZr_x)₃SiC₂ solid solutions measured by an ultrasonic pulse-echo method (325–354 GPa) are in good agreement with the predicted elastic moduli (357–342 GPa).