First-principles study on the stability and electronic structure of Mg/ZrB2 interfaces

The geometric optimizations, values of the ideal work of adhesion, interface energies and electronic structures of Mg(001)/ZrB2(001) interfaces with different stacking sequences (top, center and bridge) were studied by the plane wave pseudopotential method based on the first-principles density functional theory (DFT). The results show that the B-terminated top-site (top1 and top2) interfaces have little change and the B-terminated bridge-site interface transforms into a new B-terminated center-site interface, and both the Zr-terminated top- and bridge-site interfaces transform into new Zr-terminated center-site interfaces after geometry optimizations. The bond lengths of Mg-B, interfacial distances and values of the ideal work of adhesion of the newly formed center-site interfaces and the optimized original center-site interfaces are close to each other. The B-terminated center-site interface is the most stable as it has the largest value of the ideal work of adhesion and the smallest interfacial distance. The values of the ideal work of adhesion of the sub-interface regions indicate that the interfaces can improve the bond strengths of the sub-interfaces in Mg side while weaken those in ZrB2 side. The B-terminated (Zr-terminated) center-site interface has negative interface energy and can be formed spontaneously in B-rich (poor) environment. The B-terminated center- and top-site interfaces have both ionic bonds and covalent bonds which exhibit strong directionality in the B-terminated center-site interface. ZrB2 particles are suitable to be used as effective nucleants to refine the grain size of Mg alloy or as reinforcements to prepare Mg matrix composites due to the strongly bonded Mg/ZrB2 interfaces.