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The elaboration of nanostructures including both functional materials and functional morphology is a crucial scientific and technological challenge. In this work diatom frustule replicas mainly consisting of magnesium silicon nitride and nanocrystalline silicon have been obtained by simultaneous metallothermic reduction and nitriding of silica diatom frustules at 800 °C. The frustule replicas retained most of the complex nanoporous structures from the original frustules in the conversion. The optical scattering, transmittance and luminescence properties of the replicas have been investigated. Luminescence was observed and attributed to the presence of silicon nanocrystals. Wavelength dependent diffraction of light was observed in bio-silica frustules but not in frustule replicas, this was attributed to surface coarsening of the replicas during reaction. Light transmittance was found to be lower in frustule replicas and was consistent with absorption of light by Si nanocrystals.

Layered Li[Ni0.8Co0.1Mn0.1]O2 cathode materials have been prepared by sol–gel and co-precipitation methods. The structural, morphological and electrochemical properties of the materials were compared. The XRD patterns show that both the sol–gel and the co-precipitation method formed single phase materials with good layered characteristics. Rietveld refinement reveals some differences in cation disorder between the two materials, where the sample synthesized by the sol–gel method shows lower Li/Ni cation disorder. SEM and BET measurements show that the sol–gel sample consists of relatively less aggregated particles giving larger BET surface area compared to the co-precipitation sample. Electrochemical tests indicate that the material prepared by the sol–gel method has slightly better electrochemical properties, with an initial discharge capacity of 200 mAh·g− 1 and capacity retention of 82.2% after 50 cycles at a cycling rate of 0.5 C, as well as better capability at 5 C. The improved performances of the sol–gel synthesized material may be attributed to the low Li/Ni disorder combined with high surface area, the latter increasing the interfacial contact area between the electrolyte and the active material. Effects of calcination conditions on the structure and electrochemical performance of the materials were also investigated. The electrochemical performance was improved by either increasing the O2 concentration in the calcination atmosphere, or by increasing the flow rate of air, showing the potential of developing low-cost synthesis routes for high-quality cathode materials.

The crystal structure, anisotropic thermal expansion and structural phase transition of the perovskite LaFeO3 has been studied by high-temperature X-ray diffraction from room temperature to 1533 K. The structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R 3 ¯ c structure of LaFeO3 is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes. Non-linear lattice expansion across the antiferromagnetic to paramagnetic transition of LaFeO3 at TN=735 K was compared to the corresponding behavior of the ferroelectric antiferromagnet BiFeO3 to gain insight to the magnetoelectric coupling in BiFeO3, which is also multiferroic. The first order phase transition of LaFeO3 from Pbnm to R 3 ¯ c was observed at 1228±9 K, and a subsequent transition to P m 3 ¯ m was extrapolated to occur at 2140±30 K. The stability of the Pbnm and R 3 ¯ c polymorphs of LaFeO3 is discussed in terms of the competing enthalpy and entropy of the two crystal polymorphs and the thermal evolution of the polyhedral volume ratio VA/VB.

One important challenge, among several others, in using silicon nanostructures as anodes in lithium ion batteries concerns finding cost effective fabrication routes for their connection to a suitable current collector. Here we present synthesis and characterization of silicon nanostructures by plasma enhanced chemical vapor deposition and template assisted electrodeposition on conducting substrates. The two methods give materials with different morphologies. Silicon nanowires were grown by chemical vapor deposition utilizing the gold catalyzed vapor-liquid-solid growth mechanism. A decrease in the nucleation time for silicon wire growth on stainless steel and aluminum substrates was observed with increasing growth temperature and SiH4 pressure. The utilization of plasma enhancement resulted in the formation of silicon thin films. Copper substrates, without diffusion barrier, were found to be unsuitable for gold catalyzed vapor-liquid-solid growth. Silicon films and dots were deposited on copper and copper/gold substrates by template assisted electrochemical deposition in ionic liquids.

Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3−δ and compared to CaTi0.6Fe0.15Mn0.25O3−δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 °C and as function of feed side pO2 from 10−2 to 1 bar, and at high pressures up to 4 bar with a pO2 of 3.36 bar. The O2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9×10−3 mL min−1 cm−1 at 900 °C for a feed side pO2 of 0.21 bar. The O2 permeability of CaTi0.6Fe0.15Mn0.25O3−δ shows little variation with increased feed side pressures and reaches 1.5×10−2 mL min−1 cm−1 at 900 °C for a feed side pO2 of 3.36 bar. This is approximately 1.5 times higher than the O2 permeability with a feed side pO2 of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3−δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 °C; the results indicate a high creep resistance for this class of materials. The measured O2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability.

The fracture strength, fracture toughness and apparent Young’s modulus of LaFeO3 ceramics in the temperature region 25–800 °C are reported. The fracture strength of the material was observed to increase from 202 ± 18 MPa at room temperature to 235 ± 38 MPa at 800 °C. The room temperature fracture toughness was 2.5 ± 0.1 MPa m1/2. The fracture toughness decreased to 2.1 ± 0.1 MPa m1/2 at 600 °C, followed by an increase to 3.1 ± 0.3 MPa m1/2 at 800 °C. The temperature dependence of the fracture toughness correlates well with the crystallographic strain, |(a−c)|/(a+c), and ferroelastic toughening of LaFeO3 materials is inferred. Non-elastic stress–strain behaviour of the LaFeO3 materials due to ferroelasticity was confirmed by cyclic compression experiments, and residual strain was observed in the material after unloading.

The densification, microstructure and phase evolution of Sr4Fe6−xCoxO13 (0≤x≤4) materials have been investigated by powder X-ray diffraction, electron microscopy and thermal analysis. Powders were prepared by the solid state reaction method or by the EDTA precursor method. Pure Sr4Fe6O13 is stable above 775±25°C in air until it melts peritectically at 1220±5°C. Below 775°C, Sr4Fe6O13 is unstable with respect to the formation of Sr1−xFeO3−δ and SrFe12O19. Co substituted Sr4Fe6O13 is only stable in a narrow temperature region near 900°C. At higher or lower temperature, the Co-content is reduced due to formation of the perovskite SrFe1−zCozO3−δ and the solid solutions Co3−yFeyO4 (below 900°C) or Co1−yFeyO (above 900°C). A plate-like morphology of Sr4Fe6−xCoxO13 grains was observed both in calcined powders and in sintered ceramics. Ball milling of the calcined powders was necessary prior to the sintering in order to achieve dense materials in the temperature region 1120–1170°C. Only pure Sr4Fe6O13 appeared as a single-phase material after sintering. Increasing amounts of the phases SrFe1−zCozO3−δ and Co1−yFeyO were observed with increasing sintering temperature and increasing Co-content due to the limited solubility of Co in Sr4Fe6−xCoxO13. The thermal expansion coefficient of the materials deviates from linear behavior due to the decreasing oxidation state of iron with increasing temperature. The present investigation demonstrates that Sr4Fe4Co2O13 materials with high oxygen permeability are not single-phase materials when sintered at high temperature.

LaCoO3 and LaFeO3 based perovskites have been studied as model materials for oxygen permeable membranes. To avoid gas leakages it is of crucial importance to obtain dense membranes, hence the densification behavior in terms of temperature, stoichiometry (AB-ratio), presence of secondary phases and substituents (Ca and Sr) have been investigated. Only a narrow temperature window for the sintering is available and it is important to avoid the formation of secondary phases. The upper temperature to obtain high density materials is limited by a severe swelling. Mechanical properties such as bending strength and fracture toughness have been determined both at ambient- and elevated temperatures. Non elastic behaviour due to ferroelasticity is reported for pure LaFeO3, LaCoO3 and La0.8Ca0.2CoO3. The ferroelasticity is found to influence the behavior of the fracture toughness and fracture strength as a function of temperature. The electrical conductivity of pure LaFeO3 at 1000°C is determined in terms of partial pressure of oxygen. Cation diffusion is found to be rate controlling for the establishment of a time independent conductivity in the p-conductivity regime.