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We report on the growth of cuprous oxide on MgO(001) by plasma-assisted molecular beam epitaxy. An increased copper to oxygen ratio enhances the cube-on-cube growth of the Cu 2 O crystallites compared to the Cu 2 O(110)||MgO(100) oriented crystallites. This correlates with the occurrence of a (3√2×√2)R45° surface reconstruction observed during growth. This reconstruction is known to be unstable under oxygen-rich conditions and stabilizes the Cu 2 O(001) surface compared to the Cu 2 O(110) surface for higher copper to oxygen ratios enhancing cube-on-cube growth. High resolution X-ray diffraction analysis of the resulting cube-on-cube Cu 2 O layers indicates partial relaxation by 39.7%. Investigations of the optical absorption and photoluminescence properties of the films reveal excitonic contributions comparable to those of single crystals. [ABSTRACT FROM AUTHOR]

Abstract: Lithium tantalate (LT) is an oxide material whose congruent composition differs from its stoichiometric composition in the Li2O–Ta2O5 binary system. Ionic species in the LT melt are segregated during crystal growth, even at the congruent composition, which leads to crystallization electromotive force (C-EMF) at the solid–liquid. On the other hand, when a compound has a stoichiometric structure at the congruent composition, such segregation does not occur. By employing a new concept of stoichiometry of a material where the activity of any constituent element could be unity, we developed a new lithium tantalate with MgO doping, cs-MgO:LT (Li2O:Ta2O5:MgO=40.8:50.0:9.2), that is stoichiometric and coincident with the congruent composition. Because of this coincidence, cs-MgO:LT does not yield C-EMF and does not show segregation during growth even for ionic species. A bulk crystal was grown from the melt of the cs-MgO:LT composition via the Czochralski (CZ) method, and it showed excellent compositional homogeneity, proved by the constant distribution of the Curie temperature throughout the crystal. [Copyright &y& Elsevier]

Abstract: Transition metal ions (Mn2+, Cr3+, Fe2+/3+, V2+) as substitutional impurities in cubic crystals play an important role due to their influence on the magneto-optical properties of the virgin crystals. The optical and magnetic properties of commercial MgO(001) single crystals were investigated. The PL spectra of 3d impurity ions (Cr3+ and V2+) show narrow zero phonon lines with decay times in the range of milliseconds and a broad multiphonon sideband decaying in microseconds. The EPR study exhibits hyperfine components corresponding to Mn atoms and to V atoms located in orthorhombic symmetry. The intensity change of the EPR and PL spectra as well as the variation of the decay time with temperature can be explained by electron-spin lattice relaxation due to the Raman process. [Copyright &y& Elsevier]