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[en] The reflectivity spectra at near normal incidence in the spectral range 1.5 μm to 4 μm of EuO single crystals slightly rich in Eu but almost stoichiometric have been measured in the temperature range 4.2 to 300 K, using the Voigt configuration. Two dips are observed at 1.85 and 2.20 μm in fairly good agreement with the location of the two absorption peaks observed in similar materials. These peaks are ascribed in the literature either to optical transitions of an electron bound to an oxygen vacancy or to transitions into F centres formed at the vacancies. Our measurements show a very small temperature dependence of the energy position of the dips in the whole range [4.2-300K] and a small intensity of the dips, which is in favour of the first interpretation when the material is an insulator, and of an alternative one in the metallic configuration, i.e. an interband transition between up and down spin subbands. At 4.2 K, two extra dips appear at 1.74 and 2 μm. The magnetic field up to 30 kG does not affect the energy position of the different dips, but greatly affects their shape
[en] Highlights: • A novel template based on the 1x5 surface reconstruction of Eu protects the interface and promotes oxide growth on silicon. • The atomic structure of the template supports a high metal coverage necessary for epitaxial coupling of oxides with silicon. • The advantage of the novel template is demonstrated as coming from suppressed surface oxidation. • The potential of the new template is exemplified by successful synthesis of the archetypal spintronic system EuO/Si. Epitaxial integration of oxides with the ubiquitous silicon technological platform promises devices with dreamed-of functionality but is difficult to achieve due to chemical processes at the Si/oxide interface. The standard approach suggests a protective template – a surface superstructure of SrSi2 stoichiometry; still, only a handful of oxides couple to Si with atomically abrupt interface. We advocate an alternative approach – the use of metal-rich submonolayer templates as a general recipe, in particular, robust 1 × 5 reconstructions of Sr and Eu on Si. Their fail-safe synthesis is reported, diffraction techniques and electron microscopy reveal the structure and thermal stability of the reconstructions. The surface protection is discussed in terms of oxidation kinetics. The advantages of the new templates are demonstrated recruiting the example of the paradigmatic spintronic system EuO/Si.
[en] The pressure-volume relationship for EuO was investigated to 630 kilobars at room temperature with a diamond-anvil, high-pressure cell. Volumes were determined by x-ray diffraction; pressures were determined by the ruby R1 fluorescence method. The preferred interpretation involves normal compression behavior for EuO, initially in the B1 (NaCl-type) structure, to about 280 kilobars. Between approx. =280 and approx. =350 kilobars a region of anomalous compressibility in which the volume drops continuously by approximately 2% is observed. A second-order electronic transition is proposed with the 6s band overlapping with the 4f levels, thereby reducing the volume of EuO without changing the structure. This is not a semiconductor-to-metal transition. In reflected light, this transition is correlated with a subtle and continuous change in color from brown-black to a light brown. The collapsed B1 phase (postelectronic transition) is stable between approx. =350 and approx. =400 kilobars. At about 400 kilobars the collapsed B1 structure transforms to the B2 (CsCl-type) structure, with a zero pressure-volume change of approximately 12 +/- 1.5%
[en] The Eu-Ta-O system was examined near the composition Eu3TaO6. As found by others, Eu3/sup II/ TaO5.5 does not exist under the preparative conditions used (argon, welded Mo crucibles, 12000 to 22000C). Product mixtures consist of EuO, a phase near Eu2/sup II/Eu/sup III/TaO6 and probably Ta
[en] Rare earths ions owing to the similarity in size with thorium ions have considerable solid solubility in ThO_2 to form FCC fluorite-type solid solution. In the present study a series of solid solutions containing EuO_1_._5 in ThO_2 were prepared by co-precipitation method. These solid solutions were characterized for their composition by standard wet-chemical analysis. Their bulk and theoretical densities were determined by immersion and X-ray techniques respectively. The extent of solubility of EuO_1_._5 in ThO_2 matrix was determined using powder X-ray diffraction at 1473 K. The terminal solubility of EuO_1_._5 was found to be in the range 52.3 to 52.8 mol %. (author)