Mixed cation phases in sputter deposited HfO2 -Ti O2 nanolaminates

Abstract

Nanolaminate Hf O2 -Ti O2 films are grown by reactive sputter deposition on unheated fused Si O2, sequentially annealed at 573 to 973 K, and studied by x-ray diffraction. A nanocrystalline structure of orthorhombic (o) HfTi O4 adjacent to an interface followed by monoclinic (m) Hf1-x Tix O2 is identified. m- Hf1-x Tix O2, a metastable phase, is isomorphous with m-Hf O2 and a high pressure phase, m-HfTi O 4. A Vegard's law analysis shows that the Ti atomic fraction in m- Hf1-x Tix O2 is much greater than Ti equilibrium solubility in m-Hf O2. A space group-subgroup argument proposes that m- Hf1-x Tix O2 arises from an om-HfTi O4 second order phase transition to accommodate the larger Hf atom. © 2008 American Institute of Physics.