Synthesis and characterization of the atomic laminate Mn2AlB2

Herein, we synthesize dense, predominantly single-phase polycrystalline samples of the Mn2AlB2 ternary compound, using reactive hot-pressing of manganese, aluminum, and boron powder mixtures under vacuum. With a Vickers hardness of 8.7 GPa, Mn2AlB2 is relatively soft for a transition metal boride and lacked dominant cracks at the corners of the indentations. With Young's and shear moduli of 243 GPa and 102 GPa at 300 K, respectively, it is reasonably stiff. The Poisson's ratio is calculated to be 0.19. With compressive strengths of 1.24 ± 0.1 GPa, the samples were quite strong considering the grain size (1-15 μm). The electrical resistivity at 300 K was ∼5 μΩm and decreased linearly upon cooling. At 0.0036 K−1, the temperature coefficient of resistivity was relatively high compared to MoAlB. The average linear thermal expansion coefficient was also found to be relatively high at 18.6 × 10-6 K−1 from 298 to 1173 K. Mn2AlB2 was not thermally stable above ∼1379 K. While Mn2AlB2 was not machinable with conventional tooling, intriguingly, high-speed carbide tools bits readily penetrate the surface - with no cracking or chipping for a few millimeters - before stopping.