Phase selection and transition in Hf-rich hafnia-titania nanolaminates

Journal Article · Wed Jun 15 00:00:00 EDT 2011 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3597321· OSTI ID:21538442

Cisneros-Morales, Massiel Cristina; Rubin Aita, Carolyn

Hf-rich hafnia-titania nanolaminate films with five HfO{sub 2}-TiO{sub 2} bilayer architectures (0.64 to 0.94 Hf atom fraction) were sputter deposited on unheated fused silica substrates, annealed post-deposition from 573 to 1273 K, and analyzed by x-ray diffraction to study phase selection and transition. Isochronal annealing for 1 h intervals from 573 to 1173 K produces weak crystallization into monoclinic (m) HfO{sub 2} doped with Ti, i.e., m-Hf{sub 1-x}Ti{sub x}O{sub 2}. The amount of Ti incorporated into m-HfO{sub 2} depends upon both architecture and overall stoichiometry, but in all but the coarsest architecture, exceeds the bulk solubility limit of x = 0.05. Initial annealing at 1273 K produces significant crystallization into a biphasic structure, m-Hf{sub 1-x}Ti{sub x}O{sub 2} and orthorhombic (o) HfTiO{sub 4}. From bulk phase equilibrium considerations, o-HfTiO{sub 4} is expected to crystallize under conditions of interfacial bilayer mixing. However, upon further annealing at 1273 K, o-HfTiO{sub 4} proves to be unstable. o-HfTiO{sub 4} demixing inevitably occurs independent of architecture and stoichiometry, resulting in final crystallization products after 96 h at 1273 K that are m-Hf{sub 1-x}Ti{sub x}O{sub 2} with x {approx_equal} 0.05 and TiO{sub 2} doped with Hf. We suggest that o-HfTiO{sub 4} instability arises from a driving force to form domains similar to those found in the low temperature in/commensurate structures of ZrTiO{sub 4}. A detailed crystallographic group-subgroup analysis of the o (Pbcn) {yields} m (P2{sub 1}/c) transition shows that these domains can be represented by an orientation twin in the latter structure and their creation can be achieved by a single step second-order phase transition.

• OSTI ID: 21538442
• Journal Information: Journal of Applied Physics, Vol. 109, Issue 12; Other Information: DOI: 10.1063/1.3597321; (c) 2011 American Institute of Physics; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
ANNEALING
CRYSTALLIZATION
CRYSTALLOGRAPHY
DOPED MATERIALS
HAFNIUM OXIDES
INFRARED SPECTRA
LAYERS
MONOCLINIC LATTICES
NANOSTRUCTURES
ORTHORHOMBIC LATTICES
STOICHIOMETRY
SUBSTRATES
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THIN FILMS
TITANIUM OXIDES
X-RAY DIFFRACTION
CHALCOGENIDES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
FILMS
HAFNIUM COMPOUNDS
HEAT TREATMENTS
MATERIALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
REFRACTORY METAL COMPOUNDS
SCATTERING
SPECTRA
SPECTROSCOPY
TEMPERATURE RANGE
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS