title: ɛ-TiO, a Novel Stable Polymorph of Titanium Monoxide.
abstract: For the Ti/O system, three titanium monoxide (TiO) phases (α, β, and γ) with defective NaCl-type structures and a high-temperature hexagonal phase (H) have been known for decades. In this work, single crystals of a novel polymorph, ɛ-TiO, were synthesized by using a bismuth flux. X-ray diffraction (XRD) revealed a hexagonal crystal structure (a=4.9936(3) Å, c=2.8773(2) Å, P6‾ 2m) that is isotypic with ɛ-TaN. While the Ti atoms are surrounded by trigonal prismatic (sixfold coordination) and trigonal planar (threefold coordination) arrangements of O atoms, the O atoms are found in a pseudo-square-pyramidal arrangement of Ti atoms. First-principles calculations of the formation enthalpy and the electron and phonon density of states and crystal orbital Hamilton population (COHP) analysis revealed that ɛ-TiO is more stable than α-TiO, which had previously been regarded as the most stable phase at low temperatures.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Shinsaku
authors.initials: S
authors.lastname: Amano
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056, Aachen, Germany.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Bogdanovski
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan. yamane@tagen.tohoku.ac.jp.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Yamane
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Masami
authors.initials: M
authors.lastname: Terauchi
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056, Aachen, Germany. drons@HAL9000.ac.rwth-aachen.de.
authors.forename: Richard
authors.initials: R
authors.lastname: Dronskowski
keywords: chemical bonding; computational chemistry; phase stability; polymorphism; titanium monoxide