Formation and crystal chemistry of cubic ternary phases with filled Th6Mn23-type and AuCu3-type in the systems Ti–MVIII–Al

Crystal chemistry of the G-phase region in the Ti–Co–Al system

“…In order to elucidate the construction principle of the G-phase as a function of Al/Ti substitution with simultaneous increase in Co-content several model atom distributions were developed and studied as outlined in the following. The basis for all these models is formed by our previous information [1,2] on the atom site preference in G-phases of composition TiMAl w2 . This information was gathered via combined X-ray single crystal and powder diffraction assisted by electron diffraction and by neutron powder diffraction in the case of Ti 22.5 Ni 24.5 Al 53 .…”

“…In all cases the crystal structure of these compounds was confirmed to be a novel filled variant of the Th 6 Mn 23 type (space group Fm 3m) as earlier suggested by [3,4] from Rietveld refinement of X-ray powder diffraction data. Single crystal X-ray data [1,2] revealed a rather high atom order reflecting a number of common features in the architecture of the G-phases at Al-rich compositions. The sites 4a (M1) and 24d (M3) host only atoms of the 8th group element M, whilst Ti-atoms preferably occupy the 24e site (M4) and Al-atoms prefer the 4b (M2) and the two 32f sites, M5 and M6.…”

“…But only the composition range from 50 to 55 at.% Al is common to all G-phases. In order to elucidate the general building principle of the crystal structure of these compounds we focused in our previous articles [1,2] on the X-ray investigation of single crystals containing 45-55 at.% Al. In all cases the crystal structure of these compounds was confirmed to be a novel filled variant of the Th 6 Mn 23 type (space group Fm 3m) as earlier suggested by [3,4] from Rietveld refinement of X-ray powder diffraction data.…”

“…Insert shows the extension of the homogeneity regions for various Ti-M-Al based G-phases (M is 8th group metal, for details see[2]). …”

Solidus surface of the Al–Ti–Pd system in the Al–AlPd–TiPd–Ti region

“…The solubility of the third element in Al-Ti and Al-Pd binary compounds is no more than 2.5 at.%. The structures of the τ 1 and τ 2 ternary cubic phases are examined in the paper [2] using neutron powder and single-crystal diffraction. According to [3], the Al-Ti-Pd system has a structural variant of the τ 3 phase with Nb(Ir,Al) 2 prototype (superlattice of MgZn 2 type, P6 3 /mcm).…”