Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900~℃.Cr2AlB2 exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-...Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900~℃.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℃.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-CrBnanosheets 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.展开更多
First-principles calculations of the structural, optical, and thermal properties of Cr2AlB2 are performed using the pseudopotential plane-wave method within the generalized gradient approximation （GGA）. Calculation ...First-principles calculations of the structural, optical, and thermal properties of Cr2AlB2 are performed using the pseudopotential plane-wave method within the generalized gradient approximation （GGA）. Calculation of the elastic constant and phonon dispersion indicates that Cr2AlB2 is mechanically and thermodynamically stable. Analysis of the band structure and density of states indicates that Cr2AlB2 is metallic. The thermal properties under increasing temperature and pressure are investigated using the quasi-harmonic Debye model. The results show that anharmonic effects on Cr^AlB~ are important at low temperature and high pressure. The calculated equilibrium primitive cell volume is 95.91 ~3 at T = 300 K, P - 0 GPa. The ability of Cr2AlB2 to resist volume changes becomes weaker with increasing temperature and stronger with increasing pressure. Analysis of optical properties of Cr2AlB2 shows that the static dielectric function of Cr2AlB2 is 53.1, and the refractive index no is 7.3. If the incident light has a frequency exceeding 16.09 eV, which is the plasma frequency of Cr2AlB2, Cr2AlB2 changes from metallic to dielectric material.展开更多
基金financial supports from the National Natural Science Foundation of China under grant No. 51672064, No. U1435206 and No. 61271049
文摘Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900~℃.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℃.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-CrBnanosheets 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.
基金This work was supported by the National Natural Science Foundation of China （Grant No. U1304111）, the Program for Science ＆ Technology Innovation Talents in Universi- ties of Henan Province （Grant No. 14HASTIT039）, and the Inno-vation Team of Henan University of Science and Technology （Grant No. 2015XTD001）.
文摘First-principles calculations of the structural, optical, and thermal properties of Cr2AlB2 are performed using the pseudopotential plane-wave method within the generalized gradient approximation （GGA）. Calculation of the elastic constant and phonon dispersion indicates that Cr2AlB2 is mechanically and thermodynamically stable. Analysis of the band structure and density of states indicates that Cr2AlB2 is metallic. The thermal properties under increasing temperature and pressure are investigated using the quasi-harmonic Debye model. The results show that anharmonic effects on Cr^AlB~ are important at low temperature and high pressure. The calculated equilibrium primitive cell volume is 95.91 ~3 at T = 300 K, P - 0 GPa. The ability of Cr2AlB2 to resist volume changes becomes weaker with increasing temperature and stronger with increasing pressure. Analysis of optical properties of Cr2AlB2 shows that the static dielectric function of Cr2AlB2 is 53.1, and the refractive index no is 7.3. If the incident light has a frequency exceeding 16.09 eV, which is the plasma frequency of Cr2AlB2, Cr2AlB2 changes from metallic to dielectric material.
