Phase pure and well crystalline Cr2AlB2: A key precursor for two-dimensional CrB

Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900 degrees C. Cr2AlB2 exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-like grain with the increase of holding time. The morphology-structure relationships of Cr2AlB2 are delicately discussed. Meanwhile, as the precursor for fabrication of Cr2AlB2, high purity CrB powders are also prepared by high-temperature reaction of B and Cr elemental powders at 1800 degrees C. CrB grains grow into regular plate-like morphology. Through Rietveld structure refinement, new sets of diffraction data are presented for both CrB and Cr2AlB2 and overlapped peak positions and intensities are revealed which make up for the deficiency of the existing data in ICDD PDF (#)32-0277 (CrB) and ICDD PDF (#)72-1847 (Cr2AlB2). Moreover, since MAB phases are precursors for preparing MBenes, 2D-CrB nanosheets are successfully prepared by completely etching out Al atomic layers from Cr2AlB2. 2D-CrB crystalizes in CrB structure with two-dimensional lamellar morphology. Simultaneously the formation mechanism of 2D-CrB is vividly depicted. A system of materials preparation from CrB to Cr2AlB2 and then to 2D-CrB is well established. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.