From binary to ternary and back to binary: Transition of electromagnetic wave shielding to absorption among MAB phase Ni 3ZnB 2 and corresponding binary borides Ni n +1B n ( n= 1, 3)

Due to the chemical inertness of nickel and boron, the preparation of nickel borides and corresponding layered ternary transition metal borides Ni₃ZnB₂ (MAB phase) has always required high-temperature and/or high-pressure conditions. Yet, an innovative and efficient approach to prepare Ni₃ZnB₂ at only 600 °C and without applied pressure is presented in this study. It is discovered that by simply adjusting the temperature, a phase transition from Ni₃ZnB₂ to Ni₄B₃ with a layered structure could be induced. This transition between binary-component and ternary-component brings about significant variation of electromagnetic wave (EMW) shielding/absorption performance of prepared borides. For instance, Ni₂B is of good EMW shielding performance (42.54 dB in X band) and Ni₃ZnB₂ is of weak EMW shielding (13.43 dB in X band); Ni₃ZnB₂ has poor EMW absorption performance (-5 dB) while Ni₄B₃ has excellent EMW absorption performance (-45.19 dB) at a thickness of 2.7 mm with effective absorption bandwidth (10.4 GHz).