Crystal structures of two orthorhombic zirconias

The crystal structures of orthorhombic zirconias formed by cooling magnesia-partially-stabilized zirconia (Mg-PSZ) (space group Pbc21) and by quenching zirconia powder from 600 degrees C and 6 GPa (space group Pbca) are compared and contrasted. It is demonstrated that the two structures are easily distinguished by the neutron powder diffraction techniques used to establish them. The occurrence of two distinct phases is hence proved. Structural relationships between these two phases and also with the in situ high-pressure structure proposed from x-ray diffraction (XRD) are discussed. In this paper the three structures are virtually indistinguishable by XRD and so the structure of the high-pressure form in situ is considered to remain unknown