Размещение водорода в оксигидриде титана

Possible models of the arrangement of hydrogen atoms at the sites of the cubic lattice of titanium oxyhydride TiOyHp with vacancies in the metallic and nonmetallic sublattices are considered. It was found that titanium oxyhydride retains the B1 type crystal lattice of the initial cubic titanium monoxide TiOy and contains structural vacancies in the metal and oxygen sublattices. Comparison of the found analytical expressions for the intensity of diffraction reflections with experimental X-ray and neutron diffraction data showed that interstitial H atoms in oxyhydrides occupy vacant octahedral positions 4(b) of the oxygen sublattice. No displacement of H atoms in tetrahedral positions 8(c) is observed. A disorder-order phase transition channel associated with the formation of an ordered monoclinic titanium oxyhydride of the Ti5O5 type was found. The distribution functions of Ti, O, and H atoms in the partially ordered monoclinic oxyhydride Ti5.33O5.12H0.74 (Ti0.89O0.85H0.12) with a Ti5O5-type structure are calculated for the first time, and the concentrations of these atoms at the positions of its lattice were found.

Exploring the Spatial Control of Topotactic Phase Transitions Using Vertically Oriented Epitaxial Interfaces

Engineering oxygen vacancy formation and distribution is a powerful route for controlling the oxygen sublattice evolution that affects diverse functional behavior. The controlling of the oxygen vacancy formation process is particularly important for inducing topotactic phase transitions that occur by transformation of the oxygen sublattice. Here we demonstrate an epitaxial nanocomposite approach for exploring the spatial control of topotactic phase transition from a pristine perovskite phase to an oxygen vacancy-ordered brownmillerite (BM) phase in a model oxide La0.7Sr0.3MnO3 (LSMO). Incorporating a minority phase NiO in LSMO films creates ultrahigh density of vertically aligned epitaxial interfaces that strongly influence the oxygen vacancy formation and distribution in LSMO. Combined structural characterizations reveal strong interactions between NiO and LSMO across the epitaxial interfaces leading to a topotactic phase transition in LSMO accompanied by significant morphology evolution in NiO. Using the NiO nominal ratio as a single control parameter, we obtain intermediate topotactic nanostructures with distinct distribution of the transformed LSMO-BM phase, which enables systematic tuning of magnetic and electrical transport properties. The use of self-assembled heterostructure interfaces by the epitaxial nanocomposite platform enables more versatile design of topotactic phase structures and correlated functionalities that are sensitive to oxygen vacancies.

‘Horror Vacui’ in the Oxygen Sublattice of Lithium Niobate Made Affordable by Cationic Flexibility

The present review is intended to interest a broader audience interested in the resolution of the several decades-long controversy on the possible role of oxygen-vacancy defects in LiNbO3. Confronting ideas of a selected series of papers from classical experiments to brand new large-scale calculations, a unified interpretation of the defect generation and annealing mechanisms governing processes during thermo- and mechanochemical treatments and irradiations of various types is presented. The dominant role of as-grown and freshly generated Nb antisite defects as traps for small polarons and bipolarons is demonstrated, while mobile lithium vacancies, also acting as hole traps, are shown to provide flexible charge compensation needed for stability. The close relationship between LiNbO3 and the Li battery materials LiNb3O8 and Li3NbO4 is pointed out. The oxygen sublattice of the bulk plays a much more passive role, whereas oxygen loss and Li2O segregation take place in external or internal surface layers of a few nanometers.

Особенности структуры и оптические свойства номинально чистых кристаллов LiNbO-=SUB=-3-=/SUB=-, выращенных из шихты, содержащей B-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

It is shown that the use of B2O3 as a flux allows us to obtain the nominally pure LiNbO3 crystals possessing high compositionally uniformity. The LiNbO3:B crystals have both the increased ordering of the structural units of the cation sublattice, close to stoichiometric crystals, and high optical damage resistance. According to the results of computer simulation it was found that the boron element can incorporate into the faces of oxygen tetrahedra of the LiNbO3 crystal structure. Trace amounts of boron (10⋅10-4 wt. %) in the LiNbO3:B structure prevent the formation of the point defects (NbLi). At the same time, B3+ noticeably deforms the oxygen sublattice of the LiNbO3 crystal structure thereby it changes the polarizability of the oxygen octahedra, which determines the nonlinear optical properties of the crystal.

Anomalous hydrogen dynamics of the ice VII–VIII transition revealed by high-pressure neutron diffraction

Above 2 GPa the phase diagram of water simplifies considerably and exhibits only two solid phases up to 60 GPa, ice VII and ice VIII. The two phases are related to each other by hydrogen ordering, with the oxygen sublattice being essentially the same. Here we present neutron diffraction data to 15 GPa which reveal that the rate of hydrogen ordering at the ice VII–VIII transition decreases strongly with pressure to reach timescales of minutes at 10 GPa. Surprisingly, the ordering process becomes more rapid again upon further compression. We show that such an unusual change in transition rate can be explained by a slowing down of the rotational dynamics of water molecules with a simultaneous increase of translational motion of hydrogen under pressure, as previously suspected. The observed cross-over in the hydrogen dynamics in ice is likely the origin of various hitherto unexplained anomalies of ice VII in the 10–15 GPa range reported by Raman spectroscopy, X-ray diffraction, and proton conductivity.

Perovskite hetero-anionic-sublattice interfaces for optoelectronics and nonconventional electronics

Perovskite hetero-anionic-sublattice interfaces can provide a new platform for emergent phenomena that may or may not have homo-oxygen-sublattice interface analogues.

Structure change of monoclinic ZrO2 baddeleyite involving softenings of bulk modulus and atom vibrations

Monoclinic ZrO2 baddeleyite exhibits anomalous softenings of the bulk modulus and atom vibrations with compression. The pressure evolution of the structure is investigated using neutron powder diffraction combined with ab initio calculations. The results show that the anomalous pressure response of the bulk modulus is related not to the change in the bonding characters but to the deformation of an oxygen sublattice, especially one of the layers made of oxygen atoms in the crystallographic a* plane. The layer consists of two parallelograms; one is rotated with little distortion and the other is distorted with increasing pressure. The deformation of this layer lengthens one of the Zr—O distances, resulting in the softening of some atom vibrational modes.

The Effect of Protonation on Structural Modification in Layers

The results on protonation in solutions and melts of salts and acids, as well as structural changes associated with the formation of nanocomposition structure of materials are presented. It is shown by structural methods that proton localization is invariant to the volume in the protonated layer and is accompanied by changes between oxygen distances, enlargement of the unit cell and transition to the rhombic phase. Having the maximum crystal-chemical activity, protons create a hexagonal lattice in accordance with the features of equipotential pictures of their nonequilibrium electrostatic fields. The increase in the integral intensity of reflexes observed on neutronograms of protonated LiNbO3 (102), (111), (113) it is associated with the ordering of protons in the hexagonal oxygen sublattice of the initial phase.