Silicon is the second most abundant element on the Earth and one of the more abundant elements in our Solar System. Variations in the relative abundance of the stable isotopes of Si (Si isotope fractionation) in different natural reservoirs, both terrestrial (surface and deep Earth) as well as extra-terrestrial (e.g. meteorites, lunar samples), are a powerful tracer of present and past processes involving abiotic as well as biotic systems. The versatility of the Si isotope tracer is reflected in its wide-ranging applications from understanding the origin of early Solar System objects, planetary differentiation, Moon formation, mantle melting and magma differentiation on the Earth, ancient sea-water composition, to modern-day weathering, clay formation and biological fractionation on land as well as in the oceans. The application of Si isotopes as tracers of natural processes started over six decades ago and its usage has seen a sudden increase over the last decade due to improvements in mass spectrometry, particularly the advent of multicollector inductively coupled plasma mass spectrometers, which has made Si isotope measurements safe and relatively easy while simultaneously improving the accuracy and precision of measurements.

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We report the observation of room temperature ferromagnetism in high quality, single crystalline dilute Fe-doped BaTiO 3. The large equilibrium solubility of Fe ions in the matrix refutes uncertainties about secondary phase magnetism, which has often eclipsed this interesting field of research. While room temperature ferromagnetism is observed at and above 5% Fe concentrations, one finds a highly concave temperature dependence of the susceptibility. Using detailed ab initio calculation, this has been related to intrinsic magnetic inhomogeneities arising from positional disorder. Apart from providing a mechanism for the observed high temperature ferromagnetism, our results point out that intrinsic disorder is a generic and essential component of dilute magnetism.

In order to identify new oxide ion‐conducting materials in the ceria family of oxides, the unique effect of co‐doping is explored and a novel series of Ce0.8Sm0.2–xCaxO2–δ compositions is identified that have enhanced properties compared to the single‐doped Ce0.8Sm0.2O1.9 and Ce0.8Ca0.2O1.9 compositions. Moreover, the superior characteristics of the co‐doped Ce0.8Sm0.2–xCaxO2–δ powders prepared by the mixed‐fuel process aid in obtaining 98 % dense ceramics upon sintering at 1200 °C for 6 h. Though a linear increase in conductivity is observed by replacing Sm with Ca, the composition with the maximum amount of Ca and the minimum amount of Sm exhibits a significant improvement in properties compared to the rest in the series. The composition Ce0.80Sm0.05Ca0.15O2–δ exhibits a conductivity as high as 1.22 × 10–1 S cm–1 at 700 °C with minimum activation energy (0.56 eV) and a superior chemical stability to reduction compared to any of the hitherto known (CaSm) compositions. The absence of CeIII, confirmed both from X‐ray photoelectron spectroscopy and X‐ray absorption spectroscopy, strongly suggests that the observed increase in conductivity is solely due to the oxide ion conductivity and not due to the partial electronic contribution arising from the presence of CeIII and CeIV. To conclude, the experimental results on the Ce0.8Sm0.2–xCaxO2–δ series underscore the unique effect of calcium co‐doping in identifying a cost‐effective new composition, with a remarkably high conductivity and enhanced chemical stability to reduction, for technological applications.

The observation of finite magnetic moment in antiferromagnetic materials is quite unusual and has been immensely investigated in nanoparticle systems. Here, the structural and magnetic properties of NiO particles are explored by x-ray diffraction, extended x-ray absorption fine structure, and magnetization measurements. Using similar-sized particles with different surface defect structure, we show that the observed magnetic enhancement, which is present even beyond finite-size limit, is due to the surface effects. However, the well known spin glass freezing is found to occur only in nano-regime.