The stoichiometry, stability and polymorphism of the perovskite-related solid solutions, Lio,-~REo,,+,TiO, : RE = La, Nd, has been studied. For both series, the data are presented in the form of a temperature vs. composition phase diagram. Unit cell data for the different polymorphs (three in the La system, four in the Nd system) are presented, together with data on the composition and thermal history dependence of the lattice parameters. The phase composition and microstructure of selected ceramic samples were analysed by electron microprobe techniques.

Scandia stabilised zirconias offer much better electrical performance than conventional yttria stabilised materials; however, the limited availability and high cost of scandia have generally limited interest in its application in fuel cells. Political and economic changes over the last decade have significantly enhanced scandia's availability, rendering it worth considering for commercial application, even though there is still some uncertainty about its ultimate market price. A small addition of 2 mol% yttria to scandia stabilised zirconia results in stabilisation of the cubic phase and so avoids the major phase changes that occur on thermal cycling of scandia substituted zirconias, which might be expected to be detrimental to long term electrolyte stability. This addition of yttria does slightly impair the electrical conductivity of the scandia stabilised zirconia, although this can be reversed by further addition of ceria. Samples which are cubic throughout the studied temperature range basically show two linear conductivity regions in Arrhenius conductivity plots. A key observation is that the low temperature activation energy decreases and the high temperature activation energy increases as yttrium content increases and scandium content decreases. This correlates with the strength of short-range order as indicated by neutron and electron diffraction studies. Although scandia substitution increases conductivity and decreases high temperature activation energy, it also increases the tendency to short-range ordering at lower temperatures, resulting in a significant increase in activation energy for conduction. This is attributed to the ionic size of the Sc ion which favours a lower coordination number than that associated with ideal fluorite phases. It should also be realised that Zr, which has a similar size to Sc, also prefers a lower coordination number than is ideal for fluorite hence driving the tendency for short-range order in zirconia fluorites.

Inorganic perovskites exhibit many important physical properties such as ferroelectricity, magnetoresistance and superconductivity as well their importance as energy materials. Many of the most important energy materials are inorganic perovskites and find application in batteries, fuel cells, photocatalysts, catalysis, thermoelectrics and solar thermal. In all these applications, perovskite oxides, or their derivatives offer highly competitive performance, often state of the art and so tend to dominate research into energy material. In the following sections, we review these functionalities in turn seeking to facilitate the interchange of ideas between domains. The potential for improvement is explored and we highlight the importance of both detailed modelling and in situ and operando studies in taking these materials forward.

A new oxide of the Ruddlesden-Popper series has been isolated and structurally characterized in the Eu-Sr-Co-Mn-O system. X-ray diffraction and electron microscopy show that polycrystalline Eu 2 SrCo 1.5 Mn 0.5 O 7 constitutes the n=2 member of a homologous series, the essential feature of which is the existence of two connected Co/Mn octahedral layers, separated by Eu atoms. Electrochemical study shows that, the area-specific resistance of this compound is 0.15Ω cm 2 at 700 ºC in air, a performance which is comparable to that of the best state-of-the-art materials used as cathode in intermediate temperature solid oxide fuel cells. Below 150 K the title material presents two different magnetic phenomena. The first one corresponds to the formation of ferromagnetic nanoclusters (T C ∼121 K) within an ordered Co 2+ /Mn 4+ atomic configuration, whereas at lower temperature (∼21 K) a spin glass state occurs. Figure 3. (a) HAADF image of along Eu 2 SrCo 1.5 Mn 0.5 O 7 [0 1 0]. A schematic model for cationic position has been inserted. (b) Corresponding ABF image where cationic atoms are in red and oxygen are in blue. Interstitial oxygen ions are indicated by blue arrows. a along [110] pseudocubic axis in a given two-layer perovskite block and along [-110] direction in adjacent blocks. Physical Properties Magnetic behaviour.The magnetic behaviour of oxides is related to metal oxidation states, charge localization and ordering phenomena, which are also related with transport properties. Thus, magnetic measurements may help to understand the electrical properties of a given material.

Mg-doping effects on the crystal structure and ion conduction properties of Scandia Stabilized Zirconia have been studied in the (ZrO 2) 0.89 (Sc 2 O 3) 0.11-x (MgO) x (0  x  0.07) system. The materials have been prepared by a sol-gel method. Characterization of the crystal structure has been carried out by means of X-ray diffraction, Raman spectroscopy, synchrotron X-ray diffraction, selected area electron diffraction and high resolution transmission electron microscopy. Cubic phase-stabilization is observed in materials corresponding to x ≥ 0.03 but single cubic-phase formation is achieved only in (ZrO 2) 0.89 (Sc 2 O 3) 0.08 (MgO) 0.03. Ionic conductivity of the oxides has been determined by complex impedance spoectroscopy. Stabilization of the cubic phase in the compounds with x ≥ 0.03 values avoids rhombohedral-cubic phase transformation, improving the conductivity bellow 600 ºC compare to the one of 11ScSZ.