High Pressure Sintering And Crystal Structures Of Al-Cr Quasicrystal Systerms

The project focused on preparing binary Al-Cr quasicrystal related phases by high-pressure sintering approach,followed by resolving and refinement their crystal structures by single crystal X-ray diffractions.Firstly,a monoclinic Al₄₅Cr₇C_0.32.32 solid solution single phase was obtained serendipitously in the educts while high-pressure sintering?HPS?of Al₇Cr alloys.The determined unit cell parameters are a=20.623?2??,b=7.5900?9??,c=10.9626?13??,?=107.310?3?°with the C2/m space group.The partially occupied C atom exist in the atomic gap of the monoclinic Al₄₅Cr₇ phase and the occupying factor was 0.160?11?.The crystal structure of monoclinic Al₄₅Cr₇C_0.32.32 is similar to the approximates of Al₄₅Cr₇.All of them are layered structure,and there are icosahedral chains along the[101]direction.Secondly,a new monocline Al₄Cr phase,named?-Al₄Cr,was found in the Al₄Cr samples after HPS treatments.The unit cell parameters are a=5.1574?6??,b=17.413?2??,c=5.1107?7??,?=100.357?4?°with the Cm space group.The monoclinic?-Al₄Cr phase is found to be isomorphic to those of the Al₄Mo and Al₄W phases and there are only30 atoms in the unit cell of the monoclinic?-Al₄Cr phase.The new phase has a layered structure and consists of eight close-packed layer structures which parallel to?010?crystal plane.Finally,the"Nanoclustering"method in Topospro software were used to analysize the topological features of Al₄₅Cr₇,?-Al₄Cr,?-Al₄Cr,?-Al₁₁Cr₂ and?-Al₈Cr₅ phases that all locate at the Al-rich portion of Al-Cr binary alloy diagram.It is found that the 1@12 type icosahedral clusters exist in all the crystal structures of the studied binary Al-Cr phases.Another type of 1@12 type fifteen-hedral cluster is found to be existence in the crystal structures of Al₄₅Cr₇,?-Al₄Cr and?-Al₁₁Cr₂ three phases.In addition,a 1@12@46multilayer cluster are found in the crystal structures of both?-Al₄Cr and?-Al₁₁Cr₂ phases.