Structure and bonding at Ni-ZrO2 (cubic) interfaces formed by the reduction of a NiO-ZrO2 (cubic) composite

The Ni-ZrO2 (cubic) interfaces formed by the reduction of NiO-ZrO2 (cubic) directionally solidified eutectics (DSEs) have been studied at an atomic scale by Z-contrast scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The Ni maintains the same crystallographic orientation relationship with ZrO2 as does NiO, but the Ni twins with respect to the NiO during the phase transformation. The quantitative structural and chemical information obtained from electron imaging and spectroscopy techniques indicates that bonding at the Ni-ZrO2 interface occurs between Ni and Zr, not between Ni and O. EELS confirms that the first Ni plane is predominately metallic with less than 4% Ni2+ ions residing in the interface plane.