Julius Koettgen

University of California, Berkeley | UCB · Department of Materials Science and Engineering

Materials with a high oxygen ion conductivity and a low electronic conductivity are required for the electrolytes in solid oxide fuel cells (SOFC) and high-temperature electrolysis (SOEC). A potential candidate...

We have studied the free energy migration barriers ΔF‡ for oxygen diffusion in pure ceria and Sm-doped ceria for the temperatures 300, 700, and 1000 K. We used the density functional theory in the generalized gradient approximation and an additional Hubbard U parameter for the Ce 4f electronic states. We compare the results for the free energy dedu...

The rate of oxygen ion jumps in a solid oxide depends not only on the activation energy but also on the pre-exponential factor of diffusion. In order to allow a fully ab initio prediction of the oxygen ion conductivity in pure and samarium doped ceria we calculated the attempt frequency for an oxygen ion jump from first principles combining DFT+U,...

We investigate the dopant distribution and its influence on the oxygen ion conductivity of ceria doped with rare earth oxides by combining density functional theory and Monte Carlo simulations. We calculate the association energies of dopant pairs, oxygen vacancy pairs and between dopant ions and oxygen vacancies by means of DFT + U including finit...

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-...

Ionic conductivities of solid-state materials are crucial for the performance of various applications ranging from batteries and fuel cells to resistive switching devices. The macroscopic ionic conductivity results directly from the microscopic energy landscape of ion diffusion. Lattice site energies and migration barriers depend on lattice defects...

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets re...

Calcium dodecahydro- closo -dodecaborate, CaB 12 H 12 , has a percolating Ca migration path with low activation barrier (650 meV) and can be doped with Al, Bi, or a number of trivalent rare-earth cations.

Magnesium batteries hold potential for overcoming the safety and energy density limitations faced by Li-ion batteries. However, the development of Mg battery technology is plagued by the poor kinetics of Mg transport in solid state materials. Recently, the chalcogenide spinel structure was found to be suitable for rapid Mg ²⁺ diffusion. [1] Based o...

The oxygen ion conductivities of Sm doped ceria and Gd doped ceria are the highest for a rare-earth doped cerium oxide, which can be applied in solid oxide fuel cells (SOFC), high-temperature electrolysis with solid oxide electrolysis cells (SOEC), and high-temperature batteries. At the same time, zirconium oxide is a common impurity that has been...

Calcium dodecahydro-closo-dodecaborate, CaB12H12, was calculated to have a percolating Ca migration path with low activation barrier (650 meV). The formation of Ca vacancies required for diffusion was calculated to be thermodynamically feasible by substitution of Ca with Al, Bi, or a number of trivalent rare-earth cations

Calcium dodecahydro-closo-dodecaborate, CaB12H12, was calculated to have a percolating Ca migration path with low activation barrier (650 meV). The formation of Ca vacancies required for diffusion was calculated to be thermodynamically feasible by substitution of Ca with Al, Bi, or a number of trivalent rare-earth cations.

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 a...

Oxygen ion diffusion determines the performance of materials in energy conversion, energy storage and catalysis. For nominally pure cerium oxide, experiments measure high activation enthalpies while calculations predict low activation enthalpies. Moreover, for doped oxides, e.g. doped ceria, experiments show a high activation enthalpy for both pure...

The oxygen ion conductivity of polycrystalline samples of Sm doped ceria and of Gd doped ceria is studied as a function of doping fraction and temperature using impedance spectroscopy allowing the separation of bulk and grain boundary conductivity. The introduction of a fine spacing for the Sm dopant fraction allows the clear identification of the...

Seven MgLn 2 X 4 (Ln = lanthanoid, X = S, Se) spinels are calculated with density functional theory to have low barriers for Mg migration (< 380 meV) and are stable or...

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...

Sm-δoped ceria has one of the highest ionic conductivities reported for rare earth-δoped 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 c...

Zirconium doping in cerium oxide, as a result of intentional material engineering or unintentional impurities, impacts material properties like the reduction behavior and defect migration. In this study, we investigate the influence of zirconium doping on the conductivity of yttrium doped ceria using DFT+U calculations. We calculate the migration e...

For the development of solid oxide fuel cells (SOFC) and high-temperature electrolysis an electrolyte, which has a high oxygen ion conductivity and a low electronic conductivity, is required. Potential candidates are fluorite-structured oxides such as doped zirconia (ZrO2) and doped ceria (CeO2). The latter allows a reduction in the operating tempe...

A number of structural properties of orthorhombic Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) have been investigated by means of quantum-chemical calculations based on density-functional theory (DFT) and compared with experimental results. The role of the cation arrangements and the location of the oxygen vacancies within the orthorhombic structure have been e...