Highly Correlated Hydride Ion Tracer Diffusion in SrTiOH Oxyhydrides.

Mixed oxide hydride anion systems constitute a novel class of materials exhibiting intriguing properties such as solid-state hydride ion conduction and fast anion exchange. In this contribution we derive the kinetics of hydride ion transport in a mixed oxide-hydride system, SrTiOH , through isotope exchange and depth profiling. Density functional theory (DFT) calculations indicate that migration of H to neighboring vacant oxygen lattice sites is fast, but that long-range transport is impeded by slow reorganization of the oxygen sublattice.

Tracer diffusion of Zr and Ba in polycrystalline BaZrO.

Cation tracer diffusion in polycrystalline cubic BaZrO perovskites was studied using the stable isotopes Ba and Zr in air at 1015-1200 and 1300-1500 °C, respectively. Thin films of BaO and ZrO were deposited on polished BaZrO pellets by drop casting of aqueous precursor solutions containing the tracers. Isotope distribution profiles were recorded using secondary ion mass spectrometry.

Unravelling the fundamentals of thermal and chemical expansion of BaCeO from first principles phonon calculations.

Differentiating chemical and thermal expansion is virtually impossible to achieve experimentally. While thermal expansion stems from a softening of the phonon spectra, chemical expansion depends on the chemical composition of the material. In the present contribution, we, for the first time, completely decouple thermal and chemical expansion through first principles phonon calculations on BaCeO, providing new fundamental insights to lattice expansion.

Hydration thermodynamics of the proton conducting oxygen-deficient perovskite series BaTi1-xMxO3-x/2 with M = In or Sc.

This article establishes the effect of structure and composition on water uptake and the hydration and proton transport properties of the oxygen-deficient perovskite series BaTi1-x(In,Sc)xO3-x/2, with 0.2 ≤ x ≤ 0.7.

Hydration thermodynamics of pyrochlore structured oxides from TG and first principles calculations.

In this contribution we investigate trends in the defect chemistry and hydration thermodynamics of rare-earth pyrochlore structured oxides, RE(2)X(2)O(7) (RE = La-Lu and X = Ti, Sn, Zr and Ce). First principles density functional theory (DFT) calculations have been performed to elucidate trends in the general defect chemistry and hydration enthalpy for the above-mentioned series. Further, to justify the use of such theoretical methods, the hydration properties of selected compositions were studied by means of thermogravimetric measurements.

Determination of proton- and oxide ion tracer diffusion in lanthanum tungstate (La/W = 5.6) by means of ToF-SIMS.

Tracer diffusion of protons and oxide ions, as well as chemical diffusion of water, have been determined for the high temperature proton conductor lanthanum tungstate by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). The oxygen tracer diffusion and surface exchange coefficients, D(O)* and k(O)*, were measured after exchange anneals in water vapor enriched in H(2)(18)O between 350 and 620 °C, and the apparent activation energies were 176 and 82 kJ mol(-1), respectively. The hydrogen tracer diffusion coefficient (D(H)*) was measured between 220 and 320 °C after exchange anneals in D(2)O-containing atmospheres, and the apparent activation energy was 63 kJ mol(-1).

Defect chemistry of a BaZrO3 Σ3 (111) grain boundary by first principles calculations and space-charge theory.

Defect calculations from density functional theory are implemented with space-charge theory models to describe the equilibrium defect chemistry of a Σ3 (111) symmetric tilt boundary in BaZrO(3). As such, the space-charge potential and the concentrations of , , , NH and in the bulk, core and space-charge regions of the interface are calculated as a function of temperature and atmospheric conditions. Our results show that the core will be predominated by under hydrating conditions and that the space-charge potential increases with water vapor pressure.

Nitrogen defects in wide band gap oxides: defect equilibria and electronic structure from first principles calculations.

The nitrogen related defect chemistry and electronic structure of wide band gap oxides are investigated by density functional theory defect calculations of N(O)(q), NH(O)(×), and (NH2)(O)(·) as well as V(O)(··) and OH(O)(·) in MgO, CaO, SrO, Al(2)O(3), In(2)O(3), Sc(2)O(3), Y(2)O(3), La(2)O(3), TiO(2), SnO(2), ZrO(2), BaZrO(3), and SrZrO(3). The N(O)(q) acceptor level is found to be deep and the binding energy of NH(O)(×) with respect to N(O)' and (OH(O)(·) is found to be significantly negative, i.e.

Nitrogen defects from NH3 in rare-earth sesquioxides and ZrO2.

Effects of nitrogen defects on the electrical properties of RE(2)O(3) (RE = Nd, Gd, Er, Y) and ZrO(2) have been investigated by equilibration in ammonia (NH(3)) atmospheres in the temperature range 1000-1200 °C. The electrical conductivity in ammonia corresponded to that in H(2)-Ar mixtures of similar pO(2). However, upon replacing ammonia with an inert gas, the conductivity increases abruptly, typically one order of magnitude, before gradually returning to its equilibrium value.

Proton mobility through a second order phase transition: theoretical and experimental study of LaNbO4.

The gradual change in the crystal structure of the high temperature proton conductor LaNbO(4) through a second order phase transition and its relation to the activation enthalpy of mobility of protons have been studied by means of first principles calculations and conductivity measurements. The computations have revealed that protons diffuse by an inter-tetrahedral mechanism where the activation enthalpies of mobility are 39 and 60 kJ mol(-1) in tetragonal and monoclinic LaNbO(4), respectively. The activation enthalpy of mobility of protons for tetragonal LaNbO(4), determined from the conductivity curve, is 35 kJ mol(-1).

Local condensation around oxygen vacancies in t-LaNbO4 from first principles calculations.

First principles calculations reveal that formation of a fully ionized oxide vacancy leads to local condensation of coordination polyhedra forming Nb3O11(7-) in t-LaNbO4.