A Study of Amorphous Precursors for PbZrO3-PbTiO3 Based Ceramic Materials

Amorphous precursors for PbZrO₃ and PbTiO₃ ceramics were prepared from lead acetate and the transition metaln-propoxide inn-propanol orn-butoxide inn-butanol and hydrolysed with an excess of water. According to GLC and TGA/EGA analyses, the type of alkoxide group influences distinctly the structure of heterometallic precursors, i.e., oxo or acetate bridging, and the amounts of hydroxyl and organic groups bound to the metal network. The local environments of metal atoms in the amorphous precursors were also studied by EXAFS. The analysis reveals that in Pb−Zr precursors alkoxide groups modify the coordination spheres of the zirconium atoms. Conversely, local environments of both lead and titanium atoms within the analysed range of 3.4 A depend weakly on the type of alkoxide used.     

Electrons ejected in resonant Raman scattering of X-rays on krypton

In the resonant Raman scattering of x-rays on krypton gas the ejected electrons were investigated by a proportional counter spectrometer. The cross sections for the process were determined for three energies of the incident photons (181 eV, 89 eV, and 33 eV below theK edge). The results agree with the theoretical predictions, thus independently confirming the theory that has so far only been tested by scattered photon data. From the cross sections the width of theK-shell excited state of krypton is extracted asΓ _K =(2.75±0.10) eV.     

TheK-shell fluorescence yield of germanium

TheK-shell fluorescence yield of germanium has been determined asω _K=0.570±0.003 by the modified proportional counter technique using a special wall-less proportional counter filled with methane and small admixture of germanium hydride GeH₄. The required ratio of the total photoabsorption to the absorption in theK-shell has been obtained from the separate study of the energy dependence of the X-ray absorption in germanium.     

Structural evolution from the sol to the PbZrO<Subscript>3</Subscript> precursor powders prepared by an alkoxide-based sol–gel route

PbZrO₃ powders have been prepared by an alkoxide-based sol–gel route, starting from lead acetate, zirconium n-butoxide, and n-butanol as a solvent, and hydrolysed with different amounts of water in neutral and alkaline medium. The local environment of Zr and Pb atoms was pursued from the sol to the dried (150 °C) and heated (400 °C) powders, by extended x-ray absorption fine structure (EXAFS). The analysis of the sol revealed links between Pb and Zr, and even more links between Zr and Zr. The metal neighbourhoods in the dried powders are not influenced by the hydrolysis conditions. Pb-Zr correlations are gradually lost from the sol to the dried and heated powders, while the loss of Zr–Zr correlations is considerably lower.     

Structural evolution of the KTa0.6Nb0.4O3 alkoxide-based solutions: probing the transition metals local environment by X-ray absorption spectroscopy

The KTa_0.6Nb_0.4O₃ sols for chemical solution deposition of thin films were prepared from potassium acetate and transition metal ethoxides by the 2-methoxyethanol based route. The local environment of both transition metals after reflux times 1, 4, 24, and 48 h, whereby the crystallization behavior of the films was strongly affected, was monitored by extended X-ray absorption fine structure spectroscopy, at Ta L₃ and Nb K edges. The Ta species existed in the sols as monomers, remaining stable even with prolonged reflux time. The Ta–O–K correlations were confirmed in all cases. In contrast, the Nb-alkoxide formed dimers, with a gradual formation of oligomeric species with prolonged refluxing. The Nb–O–K correlations were present after all reflux times. The number of K neighbours around Nb increased upon refluxing, saturating at 24 h.     

Influence of the Structure of Precursors on the Crystallization of PbTiO3 Thin Films

PbTiO₃ (PT) thin films and their respective sols derived from three lead sources have been studied in order to elucidate the role of the starting materials in the crystallization of the products. EXAFS analysis of sols revealed similar oligomeric Ti-units in PT precursors derived from lead oxide or lead 2-methoxyethoxide acetate and a significantly different local Ti neighborhood in those derived from lead acetate. Structural details of the perovskite phase in the thin films follow the same pattern of similarity.     

The determination of theK-shell fluorescence yield of xenon by use of the proportional counter method

The wall-less proportional counter filled with propane with a small admixture of xenon was used as a spectrometer of electrons emitted by xenon atoms when photoelectrically excited by americium-241γ-rays and erbiumKα rays. TheK-shell fluorescence yield of xenon as extracted from spectra ammounts toω _k=0.889(1±0.01).     

TheK-shell fluorescence yield of gallium

TheK-shell fluorescence yield of gallium has been determined asω _K =0.529± 0.002 from the study of theK-capture in germanium 71 by the use of GeH₄ as gaseous source in a multiwire proportional counter system.     

Influence of synthesis method on structural and magnetic properties of cobalt ferrite nanoparticles

The Co–ferrite nanoparticles having a relatively uniform size distribution around 8 nm were synthesized by three different methods. A simple co-precipitation from aqueous solutions and a co-precipitation in an environment of microemulsions are low temperature methods (50 °C), whereas a thermal decomposition of organo-metallic complexes was performed at elevated temperature of 290 °C. The X-ray diffractometry (XRD) showed spinel structure, and the high-resolution transmission electron microscopy (HRTEM) a good crystallinity of all the nanoparticles. Energy-dispersive X-ray spectroscopy (EDS) showed the composition close to stoichiometric (~CoFe₂O₄) for both co-precipitated nanoparticles, whereas the nanoparticles prepared by the thermal decomposition were Co-deficient (~Co_0.6Fe_2.4O₄). The X-ray absorption near-edge structure (XANES) analysis showed Co valence of 2+ in all the samples, Fe valence 3+ in both co-precipitated samples, but average Fe valence of 2.7+ in the sample synthesized by thermal decomposition. The variations in cation distribution within the spinel lattice were observed by structural refinement of X-ray absorption fine structure (EXAFS). Like the bulk CoFe₂O₄, the nanoparticles synthesized at elevated temperature using thermal decomposition displayed inverse spinel structure with the Co ions occupying predominantly octahedral lattice sites, whereas co-precipitated samples showed considerable proportion of cobalt ions occupying tetrahedral sites (nearly 1/3 for the nanoparticles synthesized by co-precipitation from aqueous solutions and almost 1/4 for the nanoparticles synthesized in microemulsions). Magnetic measurements performed at room temperature and at 10 K were in good agreement with the nanoparticles’ composition and the cation distribution in their structure. The presented study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles, and consequently their magnetic properties are strongly affected by the synthesis method used.     

Structure of manganese zinc ferrite spinel nanoparticles prepared with co-precipitation in reversed microemulsions

The structure of Mn_0.5Zn_0.5Fe₂O₄ spinel ferrite nanoparticles is studied as a function of their size and the experimental conditions of their synthesis using X-ray absorption spectroscopy. The nanoparticles of different sizes down to approximately 2 nm and with a narrow size distribution were synthesized using co-precipitation in reverse microemulsions. Simultaneous refinement of the X-ray absorption fine structure (EXAFS) of three constituting metals shows a migration of Mn and Zn ions to the octahedral site of the spinel lattice compensated by the corresponding migration of the Fe ions. To a smaller extent, Mn ions switch the occupation site already in bulk and in larger nanoparticles, while a sporadic migration of Zn is detected only in the nanoparticles with sizes below approximately 5 nm. X-ray absorption near edge structure (XANES) reveals considerable variations in the position of the Mn K edge, suggesting the average Mn valence in the nanoparticles to be higher than 3+. Annealing at 500 °C relaxes the structure of as-synthesized nanoparticles toward the structure of the ceramic bulk standard. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.