The optical properties of amorphous and polycrystalline Ba x Sr 1−x TiO 3 (BST) thin films fabricated on Si(100) substrates by a sol-gel spin-coating technique were investigated by spectroscopic ellipsometry (SE). The spectrum of the extinction coefficient k was obtained by using the refractive index and structure parameters determined by SE in the photon energy range of 2.1-5.2 eV. A fourphase fitting model was employed to describe the optical properties of the BST thin films; the spectra of their optical constants and the band gap energy E g were determined by means of optimization. In addition, the refractive index dispersion data related to the short-range-order structure of the films agreed well with the single-oscillation energy model. The dependence of the refractive index, k and E g on annealing temperature were analysed. The variation of optical band gap energy with composition was investigated by changing the content of barium in the films.
A series of NH4Y3F10 sub-microcrystals had been prepared by a one-step hydrothermal route. The morphological and structural properties of the sub-microcrystals were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The results of SEM and XRD suggested that NH4Y3F10 sub-microcrystals have irregular shapes with their sizes varying from 100nm to 500nm and the structures of obtained NH4Y3F10 sub-microcrystals are cubic phase. Additionally, the down-converting(DC) phenomenon have been observed under UV excitation in (Yb3+, Nd3+) co-doped NH4Y3F10. It is found that luminescent efficiency of 10%Yb, 1%Nd co-doped NH4Y3F10 sub-microcrystals is stronger than that of 10%Yb, 5%Nd co-doped NH4Y3F10 sub-microcrystals. The energy transfer mechanism of the emission spectra of (Yb3+, Nd3+) co-doped NH4Y3F10 is discussed.
A study of the structural and magnetic properties of Cr-and Fe-doped CeO2 nanoparticles produced by the sol–gel-based method was undertaken. The crystal structure and phase, morphology, and magnetic properties of the sample were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (Raman) and physical property measurement system (PPMS). XRD and Raman studied showed that Cr-and Fe-doped did not change CeO2 original cubic fluorite crystal structure, and no ferromagnetic secondary phase was observed. SEM images showed that Cr-and Fe-doped CeO2 nanoparticles were spherical, uniform size, and good dispersion. The particle size was about 20 nm. The magnetic measurements showed that the Cr-and Fe-doped CeO2 nanoparticles presented ferromagnetic behavior at 10 and 300 K, indicating the Curie temperature was above room temperature. The magnetization diminished with the increase of the temperature. The saturation magnetization and coercivity of Fe-doped CeO2 nanoparticles were higher than that of Cr-doped CeO2 nanoparticles. Combined with the results of XRD and Raman, the ferromagnetic behavior can be attributed to the intrinsic properties of Cr-and Fe-doped CeO2 nanostructures.
Pure BiFeO3(BFO) and Bi0.9Nd0.1Fe0.925Mn0.075O3(BNFM) thin films were deposited on Pt(111)/Ti/SiO2/Si substrate by sol-gel method. X-ray diffraction analysis showed that all the films were single perovskite structure and a phase transition appeared in Nd–Mn codoped BiFeO3 thin films. Electrical measurements indicated that the ferroelectric properties of BFO thin films were significantly improved by Nd and Mn codoping. BNFM films exhibit a low leakage current and a good P-E hysteresis loop. The remanent polarization (Pr) value of 74μC/cm2has been obtained in BNFM films, while the coercive field (Ec) is 184kV/cm.
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