ABSTRACT
High-pressure scheelite phases of RVO(4) (R = Y, Sm, Gd, Yb, Lu) compounds were prepared by high pressure (up to 25 GPa) from zircon RVO(4) compounds. Raman spectra of these scheelite phases of RVO(4) were determined and discussed in detail. Mechanical properties, including bulk, shear, Young's modulus, B/G and Poisson's ratios, of the scheelite phase of RVO(4) were measured by an ultrasonic method and compared with the results calculated by density functional theory. The calculated lattice parameters and mechanical properties are in good agreement with the experimental results. The radius and states of the 4f orbital of R show distinct effects on the mechanical properties.
ABSTRACT
One dimensional Eu:La(1-x)Gd(x)VO(4) nanofibers were successfully prepared via an electrospinning method. Thermogravimetry and differential scanning calorimeter (TG-DSC), X-ray diffraction, Raman spectroscopy, scanning electron microscopy and photoluminescence were used to characterize the samples. The nanofibers crystallized well below 600 °C and with the increase of Gd contents, the nanofibers crystallized in a zircon-type structure. The Raman spectra shifted to higher frequency with the increase of Gd content for zircon Eu:La(1-x)Gd(x)VO(4). The peaks of photoluminescence spectra shift towards longer wavelength when Gd replaces La and when x = 0.4, the photoluminescence intensity reaches its maximum value. The band structure and density of states of m-LaVO(4), t-LaVO(4), t-LaGdVO(4) and t-GdVO(4) were calculated by local-spin density approximation (LSDA) band theory with Hubbard term of U. The band gap of t-LaGdVO(4) is just the average of t-LaVO(4) and t-GdVO(4). In t-LaGdVO(4), La 5p states are highly localized.
