Disorder, superlattice canting and chiral domains in zirconia–niobia ceramic alloys

The structures of the zirconia-based ceramic oxide superlattice alloy phases Nb₂Zr_x−2O_2x+1 (x ≈ 7–12) are reviewed. It is noted that recent investigations into the alloys' structure suggest they are not strictly crystalline, with consequences for their diffraction properties. It is suggested that several aspects of their behaviour may be interpreted as proper to a frustrated two-dimensional XY model, where the distinctive planes of oxygen atoms in the alloys form a lattice of planar XY `spins'. Evidence is presented for the existence of frustration, which produces superlattice canting in the model including electron-microscope evidence for the existence of domains of staggered Ising-type chirality in the alloys, as predicted for the frustrated two-dimensional XY model by Villain [J. Phys. C (1977), 10, 1717–1734].