Formation Of Pure Hexagonal Phase Research Articles

Growth and characterization of crystalline Bi2Se3 thin films on flexible metal foils by magnetron sputtering system

We report the large area thin film deposition of Bi2Se3 on flexible thin molybdenum (Mo) and titanium (Ti) metal foils using magnetron sputtering technique at temperature of 400 °C. The crystallinity of post-selenized thin film was investigated using x-ray diffraction and high intense peaks of Bi2Se3 (0006) along other planes was obtained which showed the preferred orientation along c-axis on these polycrystalline substrates. Raman spectroscopy showed three main characteristic Raman peaks i.e. A11g, E2g, and A21g which revealed the formation of pure hexagonal phase of the Bi2Se3. Field emission scanning electron microscopy studied showed hexagonal nanoflakes shape Bi2Se3 films with large granular sizes ranging from 200 to 450 nm and stoichiometry of Bi2Se3 thin film was confirmed by energy dispersive x-ray analysis. The growth of crystalline hexagonal phase of Bi2Se3 thin films on large area polycrystalline low cost flexible metal foils using magnetron sputtering system pave the way for futuristics flexible energy devices.

Molarity dependent oscillatory structural and magnetic behavior of phase pure BiFeO3 thin films: Sol–gel approach

An extensive study of oscillatory response of structural and magnetic behavior of phase pure bismuth iron oxide (BiFeO3) thin films is reported in the present study. Sol-gel method is used to synthesize BiFeO3 sols at room temperature. Molarity, being an important parameter in chemical synthesis, is varied (0.25 M, 0.3 M, 0.35 M, 0.4 M, 0.45 M, 0.5 M, 0.55 M and 0.6 M) and the effect is investigated in detail. Spin coated thin films are structurally studied by X-ray diffraction (XRD) method. Films prepared using 0.35 M and 0.5 M sols confirm the formation of pure hexagonal phase of perovskite structure with R3c (161) space group. Strengthening of BiFeO3 phase is observed after magnetic field annealing (MFA) of samples at 300 °C for 2 hours. Mixed bismuth iron oxide phases (i.e. bismuth rich or deficient) are observed in thin films prepared using rest of the sols. Preferred orientation oscillates between (122) and (315) as a function of the appearance of pure and mixed BiFeO3 phases, respectively. Refined XRD parameters show -ive tilt in bond angle (i.e. ~ -7.148°) in the films with mixed bismuth iron oxide phases. Whereas, +ive tilt (i.e. 2.55° and 4.49°) in bond angles are responsible for the appearance of phase pure bismuth iron oxide phase at 0.35 M and 0.5 M sol concentration. Room temperature ferromagnetic behavior with high value of saturation magnetization is observed for films prepared using 0.35 M (109 emu/cm3) and 0.5 M (135 emu/cm3) sols. Law of approach to saturation magnetization is used to calculate magneto crystalline anisotropy.

Effects of Mo-doping on microstructure and near-infrared shielding performance of hydrothermally prepared tungsten bronzes

Both Mo and W belong to VIB-sub-group, and possess similar ionic radii, electronegativity and oxide lattice configuration. Herein, Mo-doped (0–80at.%) tungsten bronzes, MxWO3, were hydrothermally prepared to systematically explore the influence of Mo-doping on their micro-structure and optical performance. The products adopted a hexagonal structure within 6at.% Mo-doping, and transformed into a monoclinic phase with higher Mo-doping content. Further tests suggested that 1.5at.% Mo-doping is beneficial for the formation of pure hexagonal phase and uniform nano-rod morphology. Optical measures showed that all samples exhibited high and comparable visible transmittance (70–80%), but a very different near infrared (NIR) shielding ability. The sample doped with 1.5at.% Mo demonstrated the best NIR shielding ability with a transmittance minimum of 20% at 1300nm. Further increase of Mo-doping dosage remarkably deteriorated NIR shielding ability by depressing the absorption of localized surface plasmon resonance (LSPR). However, the optical absorption from small-polaron was less influenced by the introduction of Mo. As a result, Mo-doping caused an evident blue shift of the infrared absorption peaks from 1350 to 750nm.

GdPO4:Er3+/Yb3+ nanorods: Hydrothermal synthesis and sensitivity of green emission to Yb3+ concentration

GdPO4:Er3+/Yb3+ phosphors were synthesized by a hydrothermal method with the assistant of PVP. The obtained samples were characterized by XRD, FTIR, SEM, EDS and spectrophotometer. The XRD and FTIR results indicated the formation of pure hexagonal phase for GdPO4:Er3+/Yb3+ phosphors. The SEM image showed that GdPO4:Er3+/Yb3+ phosphors have the rod-like morphology. The EDS results demonstrated that Er3+ and Yb3+ ions have been inserted into the GdPO4 host. Under the 980nm diode laser excitation, GdPO4:Er3+/Yb3+ phosphors emitted green emissions originating from the 2H11/2, 4S3/2→4I15/2 transitions of Er3+ ions. It was also found that the emission intensities of green emissions were sensitive to Yb3+ concentrations. On the basis of luminescent properties of GdPO4:Er3+/Yb3+ phosphors, we speculated the possible upconversion mechanism. The emission intensity of Er3+ ions increases with the increase of temperature, which is induced by the decreases of water molecules and the populated 2H11/2 level from the 4S3/2 level by thermal agitation.