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The crystal structures of europium niobate, EuNbO 3 , have been examined over a wide temperature range between 20 and 500 K using synchrotron X-ray diffraction. We have observed two successive structural phase transitions at 360 and 460 K. Below 350 K, EuNbO 3 adopts an orthorhombic perovskite structure (space group Imma ), which is characterized by NbO 6 octahedral tilting about the pseudocubic two-fold axis. The result differs from previous reports in which EuNbO 3 was assigned to a cubic aristotype (space group Pm 3 ¯ m ) of perovskite at room temperature. At around 360 K, EuNbO 3 undergoes a first-order phase transition to a tetragonal symmetry (space group I 4/ mcm ) with the NbO 6 octahedral tilting about the pseudocubic four-fold axis. As the temperature is further increased, the I 4/ mcm tetragonal phase changes into the Pm 3 ¯ m cubic aristotype at 460 K. The tetragonal-to-cubic transformation is characterized as a continuous phase transition. [ABSTRACT FROM AUTHOR]

Polycrystalline EuNbO3 samples are prepared by solid state reaction of stoichiometric amounts of Eu2O3 and Nb2O3 (air, 1400 °C, 1 d) to form Eu3NbO7 which in a second step is sintered with stoichiometric amounts of NbO2 and Nb (Mo foil enwrapped in evacuated silica tubes, 1200 °C, 12 h). [ABSTRACT FROM AUTHOR]

Wehave studied electronic properties of perovskite oxyhydridesATiO3–xHx(A = Ba, Sr). Epitaxial thin films of ATiO3–xHxwith various hydridecompositions, up to x= 0.58 for Ba and x= 0.45 for Sr, are prepared by the low-temperature CaH2reduction of the corresponding oxide films deposited on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(LSAT) substrates by pulsed laser deposition. Resistivitymeasurements for A = Sr show a metallic phase over a wide range ofH–composition, implying a substantial stabilizationof H 1s orbitals that should be distributed over O 2p orbitals. Onthe other hand, for A = Ba, a semiconducting behavior is seen up to∼5–8% of H–substitution. Interestingly,a similar contrasting behavior is observed in a Nb-substituted BaTiO3and SrTiO3, which suggests that a local cation–offcentering in lightly doped Ba films creates in-gap states in the bandstructure (as opposed to the Sr films), hindering the electron transport. [ABSTRACT FROM AUTHOR]

Amorphous Eu2TiO4 and EuTiO3 have been studied by a combination of the Faraday effect in the visible region and polarization-dependent x-ray absorption spectroscopy at the Eu M4,5 and L2,3 edges to examine the role of Eu 4f-5d exchange interactions on the ferromagnetic behavior. The bulk-sensitive x-ray absorption spectra (XAS) for Eu L2,3 edges show that most of the europium ions are present as the divalent state in the amorphous Eu2TiO4 and EuTiO3. The Eu M4,5 edge x-ray magnetic circular dichroism (XMCD) signals, measured for the amorphous Eu2TiO4, dramatically increase upon cooling through the Curie temperature (16 K) determined by a superconducting quantum interference device (SQUID) magnetometer. Sum-rule analysis of the XMCD at Eu M4,5 edges measured at 10 K yields a 4f spin magnetic moment of 6.6μB per Eu2+ ion. These results confirm that the ferromagnetic properties exclusively arise from 4f spins of Eu2+ In addition, for both the amorphous Eu2TiO4 and EuTiO3, the temperature and magnetic-field dependence of Eu L2,3 edge XMCD signals can be scaled with the corresponding magnetization measured by SQUID, indicating that the 5d magnetic polarization of Eu2+ is involved in the process to cause the ferromagnetic interaction between Eu2+ ions. We further discuss the origin of ferromagnetism in the amorphous system on the basis of the energy diagram of Eu 4f and 5d levels deduced from the Faraday effect in the visible region. From the wavelength dependence of Faraday rotation angles of the amorphous EuO-TiO2 system in comparison with those of the divalent Eu chalcogenides as reported previously, it is found that the magnitude of crystal-field splitting of Eu 5d levels in the former is on the same order as that in the latter, which explains an enhanced ferromagnetic exchange interaction between Eu 4f and 5d states. [ABSTRACT FROM AUTHOR]

EuTiO3-xHx (x ≤ 0.3) is prepared by low temperature CaH2 reduction of Eu2Ti2O7 and EuTiO3 (475-650 °C, 2 d) and characterized by XRD and magnetic measurements. [ABSTRACT FROM AUTHOR]