Ce3+ is known to show broad optical emission peaking in the green spectral range. For the stabilization of 3-valent cerium in ceramic phosphors such as calcium scandate CaSc2O4, often co-doping with sodium for charge compensation is performed (Na+, Ce3+ ↔ 2 Ca2+). At the melting point of CaSc2O4 (≈2110°C), however, alkaline oxides evaporate completely and co-doping is thus no option for crystal growth from the melt. It is shown that even without co-doping Ce3+:CaSc2O4 crystal fibers can be grown from the melt by laser-heated pedestal growth (LHPG) in a suitable reactive atmosphere. Reactive means here that the oxygen partial pressure is a function of temperature and pO2(T) rises for this atmosphere in such a way that Ce3+ is kept stable for all T. Crystal fibers with ≈1 mm diameter and ≤50 mm length were grown and characterized. Differential thermal analysis (DTA) was performed in the pseudo-binary system CaO–Sc2O3, and the specific heat capacity cp(T) of CaSc2O4 was measured up to 1240 K by differential scanning calorimetry (DSC). Near and beyond the melting point of calcium scandate significant evaporation of calcium tends to shift the melt composition towards the Sc2O3 side. Measurements and thermodynamic calculations reveal quantitative data on the fugacities of evaporating species.

Detailed structural studies of two lithiated metal oxides, Li2CuO2 and nanoscale LiCoO2, have been carried out using ex situ high-energy X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy (XAS) with the objective of understanding structural changes that might cause capacity loss during cycling. XRD on the cuprate was studied at various states of charge and phase composition, and the bulk state was determined by Rietveld refinement and pair density function (PDF) analysis. Results showed a largely irreversible structural change of the material upon oxidation of Cu2+ as well as CuO formation. The in-situ XAS of the LiCoO2 was analyzed through a difference method to extract the changes in the local structure that occur upon cycling in both the near edge (XANES) and extended region (EXAFS). Results suggest that cycling causes site exchange of the Co and Li ions near the surface of the nanoscale LiCoO2.

The influence of oxygenation in the magnetism, superconductivity and electronic states for the Mo0.3Cu0.7Sr2RECu2Oy (RE = Y, Er and Tm) compounds are discussed here. The magnetic measurements on the as-prepared (AP) samples suggest the existence of short-range magnetic correlations due to the presence of the paramagnetic MoV cations in the copper chain site. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high pressure oxygenated sample shows the highest superconducting transition temperature of TC = 84 K. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of X-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP material; annealing under flowing oxygen enhances both the MoVI and CuII amounts. A detailed study of the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy samples has been performed and is also discussed.

Thiolate-gold nanoclusters exhibit unique optical, magnetic and chiral properties, which are attractive for novel applications in nanotechnology. A fundamental challenge facing these nanomaterials is being able to study and understand their physical properties in various experimental conditions. To overcome this, extended X-ray absorption fine structure (EXAFS) spectroscopy can be employed to probe the Au local structure of thiolate-gold nanoclusters in a variety of conditions, providing valuable structural information from multiple bonding environments (i.e. metal-metal and metal-ligand interactions). This study discusses a methodology for conducting a multishell EXAFS fitting analysis that can be implemented for thiolate-gold nanocluster systems. Specifically, experimental and simulated EXAFS data for Au36(SR)24 nanoclusters are examined with a total of 5 scattering paths fitted to the experimental data.

CTGS (Ca3TaGa3Si2O14) is a commercially available, Czochralski-grown piezoelectric material from the langasite family that has an ordered crystal structure. It can be excited piezoelectrically up to at least 1285 °C, which is very close to the melting temperature of 1350 °C. In order to determine the loss at elevated temperatures, two different resonance techniques are used. A contactless transduction method is employed up to about 600 °C, whereas transduction involving standard keyhole-shaped film electrodes is employed up to 1285 °C. Comparison of the temperature-dependent inverse Q factor shows that contactless measurements are best suited for the lower temperature range, where sample clamping and losses caused by the electrodes contribute significantly to the total loss. However, at higher temperatures, measurement of the electrical impedance of samples with film electrodes in the vicinity of the resonance frequency proves to be suitable. Even at 1100 °C, 5 MHz CTGS resonators are found to have a Q factor of about 1200, which is great enough to enable numerous bulk-acoustic-wave applications. Further, a nearly linear temperature dependence of the resonance frequency with a temperature coefficient of 210 Hz/K makes Y-cut CTGS well suited for temperature-sensing applications.

Mn-doped CeO2 electrolytes formulated as Ce1-xMnxO2-x (0.05 ≤ x ≤ 0.25) were prepared via soft chemical technique which involved co-precipitation of Mn2+ and Ce4+ using oxalic acid as the precipitant. The optimized pH for a stable incorporation of Mn dopant into ceria was found to be pH = 10. The solubility limit of MnO in the CeO2 fluorite lattice structure was suggested to be x = 0.20. The phase composition, morphology properties and elemental analysis of the oxalate and derived-powder was characterized using X-ray diffraction, SEM and X-ray fluorescence (XRF) respectively. The electrical conductivity of sintered samples of Mn-doped CeO2 ceramics were investigated in air using AC impedance spectroscopy. The bulk conductivities of the Mn-doped CeO2 ceramics sintered at 1200 °C at a test temperature of 800 °C were determined to be 4.223 x 10-4 ohm-1 cm-1 for Mn content x = 0.10 with activation energy, Ea = 0.88 eV.

Transition metal nitrides containing metal ions in high oxidation states are a significant goal for the discovery of new families of semiconducting materials. Most metal nitride compounds prepared at high temperature and high pressure from the elements have metallic bonding. However amorphous or nanocrystalline compounds can be prepared via metal-organic chemistry routes giving rise to precursors with a high nitrogen:metal ratio. Using X-ray diffraction in parallel with high pressure laser heating in the diamond anvil cell this work highlights the possibility of retaining the composition and structure of a metastable nanocrystalline precursor under high pressure-temperature conditions. Specifically, a nanocrystalline Hf3N4 with a tetragonal defect-fluorite structure can be crystallized under high-P,T conditions. Increasing the pressure and temperature of crystallization leads to the formation of a fully recoverable orthorhombic (defect cottunite-structured) polymorph. This approach identifies a novel class of pathways to the synthesis of new crystalline nitrogen-rich transition metal nitrides.

The formation of nickel germanide has been examined over a range of low temperatures (200-400 °C) in an attempt to minimize the thermal budget for the process. Cross-sectional Transmission Electron Microscopy (TEM) was used to determine the texture of the germanide layer and the morphology and constituent composition of the Ge/NiGe interface. The onset and completion of reaction between Ni and Ge were identified by means of a heated stage in combination with in-situ x-ray diffraction (XRD) measurements. The stages of reaction were also monitored using measurements of sheet resistance of the germanides by the Van der Pauw technique. The results have shown that the minimum temperature for the initiation of reaction of Ni and Ge to form NiGe was 225 °C. However, an annealing temperature > 275 °C was necessary for the extensive (and practical) formation of NiGe. Between 200 and 300 °C, the duration of annealing required for the formation of NiGe was significantly longer than at higher temperatures. The stoichiometry of the germanide was very close to NiGe (1:1) as determined using energy dispersive spectroscopy (EDS).

New multiple layered perovskites with general formula RbLaNaxNb2+xO7+3x, x = 1 and 2, were synthesized via a ceramic method. While the triple layered compound could be obtained by simple direct reaction, the quadruple layered one was synthesized using a two-step solid state approach. The compounds were characterized by X-ray powder diffraction; the newly obtained compounds appear to be isostructural with the previously reported RbCa2Nb3O10 and RbCa2NaNb4O13 for RbLaNaNb3O10 and RbLaNa2Nb4O13, respectively. Preliminary results show that the new compounds can undergo ion exchange reactions involving alkali metals and transition metal chlorides.

Multifunctional Pr3+-doped GdPO4 nanocrystals possessing UV, visible emissions and magnetic properties were synthesized via co-precipitation and following annealing. It was revealed that as-prepared GdPO4 nanorods were transformed to nanoparticles after heat treatment at 900 °C for 2 hours. Ultimately, GdPO4:Pr3+ nanoparticles have strong UV emission under the excitation of 275 nm and visible emission under the excitation of 445 nm, which offers the optical modalities in both UV and visible range. Moreover, Gd3+-containing nanoparticles are efficient T2-weighted (negative) magnetic resonance (MR) contrast agents due to the presence of Gd3+ ions, which can be potentially applied as multimodal, photoluminescence-magnetic resonance imaging contrast agent.

In this work high-temperature X-ray diffraction has been used to investigate thermal and chemical expansion as well as overall phase stability for various cathode materials: Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), La0.3Sr0.7CoO3 (LSC37), La0.6Sr0.4CoO3 (LSC64) and La0.6Sr0.4Fe0.8Co0.2O3 (LSCF), as a function of temperature in reducing conditions. When perovskites materials are under a low oxygen partial-pressure condition, the lattice parameter and overall dimension increase. Their chemical expansion has comparable values. From the viewpoint of the stability of these phases, the high-temperature X-ray diffraction results indicate no phase decomposition can be one of the reasons for material failure at the current experimental oxygen partial pressure. LSF is most stable, while LSC and LSCF form oxygen vacancy-ordered phases and then decompose when heated to 1000°C under atmospheres with pO2 as low as 10-5 atm.

Most recently, magnetic ceramic nanoparticles have attracted considerable scientific interest from the basic research point of view and for their prospective use in chemical sensing, catalysis and electrochemical applications. In this paper we report the successful synthesis of xSnO2-(1-x)α-Fe2O3 system by hydrothermal synthesis and that of xZrO2-(1-x)α-Fe2O3 system by mechanochemical activation. The two nanoparticle systems were analyzed side-by-side using X-ray diffraction (XRD) and Mössbauer spectroscopy. The latter technique was used in its complexity, including the determination of the recoilless fraction using our dual absorber method. This was correlated with the onset of new phases in the systems of interest.