Thermodynamics shows halide perovskites to be highly unstable against oxygen. Light accelerates O2 interaction kinetics. The materials stays metastable in the dark.

Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 - δ (BSCF) is an interesting material for high temperature oxygen permeation membranes and solid oxide fuel cell cathodes, applications for which oxygen transport properties are crucial. Here oxygen isotope exchange is performed on dense BSCF films prepared by pulsed laser deposition on MgO single crystal substrates. The oxygen isotope profile is analyzed by secondary ion mass spectrometry to extract tracer diffusion coefficients D∗ and effective surface exchange constants k∗. Tracer diffusion has a low activation energy of 0.5 eV. At moderate temperatures, the related oxygen vacancy diffusion coefficient DVÖ is significantly larger than that for (La,Sr)(Fe,Co)O3−δ perovskites.

Large single crystals of LiFePO(4) have been chemically delithiated. The relevance of chemical oxidation in comparison with electrochemical delithiation is discussed. Analyses of the Li content and profiles were done by electron energy loss spectroscopy and secondary ion mass spectrometry. The propagation of the FePO(4) phase growing on the surface of the large single crystal was followed by in situ optical microscopy as a function of time. The kinetics were evaluated in terms of linear irreversible thermodynamics and found to be characterized by an induction period followed by parabolic growth behavior of the FePO(4) phase indicating transport control. The growth rate was shown to depend on the crystallographic orientation. Scanning electron microscopy images showed cracks and a high porosity of the FePO(4) layer due to the significant changes in the molar volumes. The transport was found to be greatly enhanced by the porosity and crack formation and hence greatly enhanced over pure bulk transport, a result which is supposed to be very relevant for battery research if coarse-grained powder is used.

We investigate methylammonium (MA) transport in MA lead iodide under illumination and show this, as in the dark, to be measurable but negligible when compared with the major carriers. 1 H and 13 C nuclear magnetic resonance (NMR) spectra show constant linewidths as a function of temperature, indicating the absence of significant MA diffusion. 13 C tracer-exchange experiments reveal two distinct diffusion processes, one attributed to bulk MA transport and the other most probably due to higher dimensional defects. The former process has a diffusion coefficient that is consistent with the upper limit extracted from NMR measurements. Derived bulk conductivities for MA cations are orders of magnitude below the experimental ionic conductivity, corroborating the picture of pure iodine transport under illumination, as it was previously experimentally shown only for the dark situation.