Mixed cation phases in sputter deposited HfO2-TiO2 nanolaminates

Nanolaminate HfO2-TiO2 films are grown by reactive sputter deposition on unheated fused SiO2, sequentially annealed at 573 to 973 K, and studied by x-ray diffraction. A nanocrystalline structure of orthorhombic (o) HfTiO4 adjacent to an interface followed by monoclinic (m) Hf1-xTixO2 is identified. m-Hf1-xTixO2, a metastable phase, is isomorphous with m-HfO2 and a high pressure phase, m-HfTiO4. A Vegard's law analysis shows that the Ti atomic fraction in m-Hf1-xTixO2 is much greater than Ti equilibrium solubility in m-HfO2. A space group-subgroup argument proposes that m-Hf1-xTixO2 arises from an o/m-HfTiO4 second order phase transition to accommodate the larger Hf atom. (C) 2008 American Institute of Physics.