Stabilization of cubic structure in Mn-doped hafnia

The compounds Hf1−xMnxO2−δ (x = 0–0.5) have been synthesized by conventional solid state reaction method in Ar. Rietveld analysis of X-ray diffraction data has shown that the Mn-doped HfO2 undergoes a structural transformation from monoclinic to cubic phases, which is significantly dependent on the Mn content under current synthesis conditions. The stabilized cubic structure by multivalent Mn ion doping can transform to the monoclinic structure when annealed at high temperature in air. Transmission electron microscopy and electron diffraction investigations have also confirmed the existence of the high-temperature cubic structure. A mechanism of stabilizing the high-temperature cubic phase in the Hf1−xMnxO2−δ system has been analyzed based on considerations of manganese substitution effect for hafnium ions and oxygen vacancy formation.