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Controlling functionalities, such as magnetism or ferroelectricity, by means of oxygen vacancies (VO) is a key issue for the future development of transition metal oxides. Progress in this field is currently addressed through VO variations and their impact on mainly one order parameter. Here we reveal a new mechanism for tuning both magnetism and ferroelectricity simultaneously by using VO. Combined experimental and density-functional theory studies of Eu0.5Ba0.5TiO3-��, we demonstrate that oxygen vacancies create Ti3+ 3d1 defect states, mediating the ferromagnetic coupling between the localized Eu 4f7 spins, and increase an off-center displacement of Ti ions, enhancing the ferroelectric Curie temperature. The dual function of Ti sites also promises a magnetoelectric coupling in the Eu0.5Ba0.5TiO3-��., Accepted by Physical Review B, 2017

Eu 3+ doped SiO 2 nano-crystalline glasses were prepared by sol-gel method. The broad peak of XRD pattern indicates an amorphous SiO 2 matrix. The affection of anneal time and anneal temperatures on photoluminescence (PL) properties of SiO 2 glass under different Eu 3+ doping concentration were studied systematically. It is found that the optimized anneal time is about 3 h. The excitation spectra of 2% Eu 3+ doped SiO 2 glass powder were measured under various anneal temperatures, and the optimized anneal temperature is observed around 700 °C. The fluorescence-quenching effect can be observed in the emission spectra when the annealing temperature exceeds 700 °C. The emission spectra of different molar ratio dopants were measured at an annealed temperature of 500 °C, and the concentration-quenching phenomenon has also been observed in SiO 2 glass powder when the molar ratio of Eu 3+ ion exceeds 3%. The result shows that the PL intensity approaches its maximum when the molar ratio of Eu 3+ ions in the sample is about 3%. In addition, a comparatively stronger emission spectrum at wavelength of 703 nm which is corresponding to the energy transition 5 D 0 → 7 F 4 of Eu ions is also obtained.

We report the effects of Al-doping on the structure and magnetic properties in CaBa(Co$_{1-x}$Al$_{x}$)$_4$O$_7$ (0$\leq$x$\leq$0.25). The system exhibits a structural transition from an orthorhombic symmetry to a hexagonal symmetry when the Al content exceeds $x =$ 0.1. The Curie temperature and the value of the magnetization decrease with increasing Al doping level, indicating that the ferrimagnetic ground state is gradually suppressed. The ground state eventually transits into a spin-glass state for $x >$ 0.1. Moreover, the short-range magnetic correlations, which occur at high temperatures in CaBaCo$_4$O$_7$, are found to be gradually suppressed with increasing Al content and eventually disappear for $x =$ 0.25. By comparing our results with other Co-site doping cases, we suggest that the lattice and the spin degrees of freedom are relatively decoupled in CaBaCo$_4$O$_7$., 15 pages, 6 figures, to be published in Journal of Alloys and Compounds