Amorphous and highly nonstoichiometric titania (TiOx) thin films close to metal-like conductivity

Oxygen-deficient titanium oxide films (TiOx) have been prepared by pulsed laser deposition at room temperature. Samples in their as-deposited state have an average composition of TiO1.6, are optically absorbing and show electronic conductivities in the range of 10 S cm−1. The films are metastable and consist of grains of cubic titanium monoxide (γ-TiO) embedded in an amorphous TiO1.77 matrix. Upon annealing in an argon atmosphere the electrical conductivity of the films increases and comes close to metal-like conductivity (1000 S cm−1) at about 450 °C whereas the local structure is changed: nanocrystalline grains of metallic Ti are formed in the amorphous matrix due to an internal solid state disproportionation. The highly conductive state can be frozen by quenching. During heat treatment in an argon atmosphere a stoichiometric rutile TiO2 surface layer forms due to oxidation by residual oxygen. The combination of a highly conductive TiOx film with such an approximately 20 nm thick rutile cover layer leads to a surprisingly high efficiency for the water-splitting reaction without the application of an external potential

Coordination Numbers in Sm-Doped Ceria Using X-ray Absorption Spectroscopy

Sm-doped ceria has one of the highest ionic conductivities reported for rare earth-doped cerium oxides. The high oxygen-ion conductivity can be attributed to the creation of oxygen vacancies by doping and weak defect interactions between oxygen vacancies and dopants. Especially, oxygen vacancies in the nearest neighborhood to dopants decrease the conductivity due to trapping and blocking. In this work, the local structure around the Ce cations is investigated using the extended X-ray absorption fine structure. The resulting coordination numbers of cerium coordinated by oxygen are only marginally larger than in a random oxygen vacancy distribution, explaining the large ionic conductivity

The Effect of Jump Attempt Frequencies on the Ionic Conductivity of Doped Ceria

The macroscopic oxygen ion conductivity in doped ceria is determined by the microscopic activation energy barriers and jump attempt frequencies of oxygen ion jumps. While the influence of the local jump environment on the migration energy is widely investigated, its influence on the attempt frequency is rarely investigated. In this work, attempt frequencies in Sm, Yb, and Gd doped ceria are calculated using density functional theory. Moreover, ionic conductivities for varying local jump attempt frequencies in different jump environments are investigated using Kinetic Monte Carlo simulations. For doping along the migration pathway, where the migrating oxygen ion passes between two adjacent cations, large dopants lead to an increase and small dopants to a decrease in the attempt frequency. Sm doping in nearest neighborhood to the start position of the migrating oxygen vacancy also leads to an increase in attempt frequency. Kinetic Monte Carlo simulations show that at intermediate Sm dopant fractions oxygen vacancies frequently jump toward and away from dopants explaining why for Sm doped ceria one of the highest conductivities for a ternary cerium oxide was measured due to its low dopant-oxygen vacancy association in both nearest and next-nearest neighborhood

Computational Investigation of Chalcogenide Spinel Conductors for All-Solid-State Mg Batteries

We report seven new MgLn2X4 (Ln = lanthanoid, X = S, Se) spinels that have low barriers for Mg migration (< 380 meV) and are stable or nearly stable (within 50 meV/atom of stability with respect to competing structures and compositions) as calculated with density functional theory. As the size of the Ln increases, Mg mobility is found to increase, but stability in the spinel structure is found to decrease

The oxygen ion conductivity of Lu doped ceria

The oxygen ion conductivity of polycrystalline samples of Lu doped ceria is studied using impedance spectroscopy. Lutetium doped ceria is of particular interest as Lu has a similar ionic radius as the host cation Ce. The change of the ionic conductivity as a function of the Lu dopant fraction is investigated in detail revealing a similar behavior as Sm doped ceria that has one of the highest ionic conductivity in ternary cerium oxides. In comparison with simulations, the experimental dependence of the conductivity on the dopant fraction reveals that migration barriers for oxygen vacancy jumps around Lu ions are slightly higher than for jumps in pure ceria. The absolute conductivity is small due to the strong trapping of oxygen vacancies near Lu dopants

Computational investigation of chalcogenide spinel conductors for all-solid-state Mg batteries.

Seven MgLn2X4 (Ln = lanthanoid, X = S, Se) spinels are calculated with density functional theory to have low barriers for Mg migration (&lt;380 meV) and are stable or nearly stable (within 50 meV per atom of stability with respect to competing structures and compositions). As the size of the Ln increases, Mg mobility is found to increase, but stability in the spinel structure is found to decrease