Computer simulation techniques have been used to investigate the defect chemistry of perovskite-structured ionic conductors based upon AZrO 3 (A = Ca, Ba) and LaMO 3 (M = Sc, Ga). Our studies have examined dopant site-selectivity, oxide ion migration and dopant-defect association at the atomic level. The energetics of dopant incorporation in AZrO 3 show strong correlation with ion size. We predict Y 3ϩ to be one of the most favourable dopants for BaZrO 3 on energetic grounds, which accords with experimental work where this cation is the commonly used acceptor dopant for effective proton conduction. Binding energies for hydroxy-dopant pairs in BaZrO 3 are predicted to be favourable with the magnitude of the association increasing along the series Y < Yb < In < Sc. This suggests that proton mobility would be very sensitive to the type of acceptor dopant ion particularly at higher dopant levels. Oxygen vacancy migration in LaScO 3 is via a curved pathway around the edge of the ScO 6 octahedron. Dopant-vacancy clusters comprised of divalent dopants (Sr, Ca) at the La site have significant binding energies in LaScO 3 , but very low energies in LaGaO 3 . This points to greater trapping of the oxygen vacancies in doped LaScO 3 , perhaps leading to higher activation energies at increasing dopant levels in accord with the available conductivity data.

Lithium / Tetrelides / Ionic Mobility / Crystal ChemistryLithium-transition metal (T)-tetrelides (tetr. = C, Si, Ge, Sn, Pb) are an interesting class of materials with greatly differing crystal structures. The transition metal and tetrel atoms build up covalently bonded networks which leave cavities or channels for the lithium atoms. Depending on the bonding of the lithium atoms to the polyanionic network one observes mobility of the lithium atoms. The crystal chemistry, chemical bonding, 7 Li solid state NMR, and the electrochemical behavior of the tetrelides are reviewed herein.

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The new germanide TaRhGe was prepared from the elements by arc-melting and subsequent annealing at 1020 K for 10 days. TaRhGe crystallizes with the TiNiSi-type structure, space group Pnma, Z = 4, oP12, a = 640.2(2), b = 383.2(2), c = 741.7(2) pm, wR2 = 0.0550, 432 F2 values, 20 parameters. The structure consists of a three-dimensional [RhGe] network of distorted RhGe4/4 tetrahedra with Rh-Ge distances ranging from 244 to 250 pm. The tantalum atoms are coordinated within this network by two folded and mutually tilted Rh3Ge3 hexagons. TaRhGe is Pauli-paramagnetic and shows no superconducting transition down to 3 K