Single crystals of Ga-containing MAX-phases Ti2GaC, Ti4GaC3, and Cr2GaC were grown from a metallic melt generated by an excess of Ga. This technique allows the crystal growth at different temperatures to control the product distribution. Compounds developed were Ti2GaC and TiC at 1500 °C, and Ti2GaC and Ti4GaC3 at 1300 °C. Crystal structures were refined from single crystal data. Ti2GaC and Cr2GaC were previously known, and belong to the Cr2AlC type as well as the solid solutions V2Ga1–xAlxC and Cr2Ga1–xAlxC. Ti4GaC3 is one of the few 413-phases (P63/mmc, a=3.0690(4) Å, c=23.440(5) Å) and the first Ga-containing representative. The crystal structures of MAX-phases are intergrowths of layers of an intermetallic MGa in a hexagonal stacking sequence with carbidic layers (MC)n of the NaCl type. The thickness of the layer depends from the value of n. The results of the structure refinements also demonstrate that also the structural details follow this description.
Single crystals of Ga-containing MAX-Phases (TiC)n(TiGa) (n=1, 3) were grown from a metallic melt including and characterised by X-ray diffraction. Ti4GaC3 is one of the few 413-phase and the first containing Ga.
Coordinates, displacement parameters (in 104 Å2), and site occupation factorsa.
a esd's in parentheses, U11=U22=2 U12, U23=U13=0. b In order to check for mixed occupations and/or vacancies site occupation factors were treated by turns as free variables at the end of the refinement. c Coupled refinement (see text). d Uiso.