Anisotropic grain growth of Bi4Ti3O12 in molten salt fluxes

Bismuth titanate (Bi₄Ti₃O₁₂) platelets were obtained by the molten salt synthesis method in NaCl-KCl and Na₂SO₄-K₂SO₄ fluxes, using an amorphous Bi₄Ti₃O₁₂ precursor and a mechanically mixed Bi₂O₃-TiO₂ mixture as the starting materials. It was found that the synthesizing temperature, salt species and starting materials could significantly affect the crystallization habit and morphology of Bi₄Ti₃O₁₂ platelets. Under the same processing conditions (i.e. in Na₂SO₄-K₂SO₄ flux at 1000 °C), the Bi₄Ti₃O₁₂ platelets synthesized from the Bi₂O₃-TiO₂ mixture generally showed a smaller particle size than those synthesized using the amorphous Bi₄Ti₃O₁₂ precursor. The Bi₄Ti₃O₁₂ platelets prepared in the chloride flux were faceted along either (0 0 1) or (1 1 2) planes, while those prepared in the sulfate flux were solely (0 0 1) faceted. The former system also had smaller particle size than the latter. Furthermore, the salt content and the addition of plate-like Bi₄Ti₃O₁₂ seeds in the amorphous Bi₄Ti₃O₁₂ precursor showed a strong influence on the particle size of the synthesized Bi₄Ti₃O₁₂ platelets. The particle size of Bi₄Ti₃O₁₂ platelets prepared in the sulfate flux decreased as the mole ratio of the sulfate salts to Bi₄Ti₃O₁₂ was increased from 7.9 to 23.7. And the addition of 10 wt.% plate-like Bi₄Ti₃O₁₂ seeds into the amorphous Bi₄Ti₃O₁₂ precursor led to a significant increase in the particle size of the resulting Bi₄Ti₃O₁₂ platelets.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

Spray pyrolyzed β-In2S3 thin films: Effect of postdeposition annealing

Indium sulfide thin films prepared using spray pyrolysis, with In/S ratio 2/3 in the solution, were annealed in vacuum at 300 and 400 °C. The effect of this treatment on properties of the films was studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, optical absorption, transmission and electrical measurements. Optical constants of the films were calculated using the envelope method. Annealing did not affect the optical properties of the film much, but the resistivity of the films showed a drastic decrease and the grain size increased. In₂S₃ thin films have potential use as buffer layer in photovoltaic heterojunction devices.     

All-chemically deposited Bi2S3/PbS solar cells

We report on solar cells with a cross-sectional layout: TCO/window/Bi₂S₃/PbS, in which a commercial SnO₂ transparent conductive oxide (TCO-PPG Sungate 500); chemically deposited window layers of CdS, ZnS or their oxides; n-type Bi₂S₃ (100 nm) and p-type PbS (360-550 nm) absorber films constitute the cell structures. The crystalline structure, optical, and electrical properties of the constituent films are presented. The open circuit voltage (V_oc) and short-circuit current density (J_sc), for 1000 W/m² solar radiation, of these solar cells depend on the window layers, and vary in the range, 130-310 mV and 0.5-5 mA/cm², respectively. The typical fill factors (FF) of these cells are 0.25-0.42, and conversion efficiency, 0.1-0.4%.     

Fabrication and photocatalytic activity of YMn2O5 nanoparticles

In this work, a polyacrylamide gel route is introduced to synthesize YMn₂O₅ nanoparticles. It is demonstrated that high-quality YMn₂O₅ nanoparticles with a uniform size and spherical shape can be prepared using different chelating agents. However, the average particle size of the products is found to have a dependence on the choice of the chelating agent. The sample prepared using citric acid as the chelating agent has an average particle size of ~ 45 nm, while the sample prepared by using the chelating agent EDTA has a particle size centered around 70 nm. The optical energy bandgap of the citric acid- and EDTA-resulted samples is obtained, from optical absorption measurements, to be 1.21 and 1.17 eV, respectively. The photocatalytic experiments reveal that the as-prepared YMn₂O₅ nanoparticles exhibit an interesting photocatalytic activity for oxidative decomposition of methyl red under ultraviolet and visible-light irradiation.     

Effect of composition and deposition parameters on optical properties of Ge25Sb15−xBixS60 thin films

The optical constants of the Ge₂₅Sb_15−xBi_xS₆₀ (0?x?15) chalcogenide films, either as-deposited or after being annealed at various temperatures have been computed in the spectral wavelength range 400-2400 nm from the transmittance and reflectance measurements of normally-incident light. With the increase in bismuth content, the optical energy gap (which is indirect) decreases, while the refractive index increases. The effects of film thickness, substrate type, deposition rate and γ-radiation on optical properties have been studied. The effect of thermal annealing on the growth characteristics and stability of the films has been studied using X-ray diffraction and scanning electron microscopy. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model.     

In situ fabrication of Bi2S3 nanocrystal film for photovoltaic devices

A facile wet-chemical method to prepare Bi₂S₃ thin films with flake nanostructures directly on ITO glass substrate is presented in this paper for the first time. The product was characterized by X-ray powder diffractometer (XRD), Raman spectrometer, scanning electron microscope (SEM), and atomic force microscope (AFM). The one-step solvothermal elements treatment on the ITO substrate spare time to form film by spin-coating process and the film could be tightly attached to the ITO electrode. A conjugated polymer, poly 3-hexylthiophene (P3HT), was then spin-coated on the as-prepared Bi₂S₃ film to form an inorganic-organic hybrid thin film. The photovoltaic performance of the resulting solar cell device was also investigated.     

Preparation and properties of Bi2−x As x S3 thin films by solution-gas interface technique

The solution gas interface technique by which thin films of Bi_2−x As _x S₃ were deposited is described in this paper. The semiconducting properties of the interface grown Bi_2−x As _x S₃ thin films are studied. The optical absorption, dark resistivity and thermoelectric power of the films were studied and results are reported.     

Efficient Bi → Nd energy transfer in Gd2O3:Bi,Nd

Bi³⁺,Nd³⁺ co-doped Gd₂O₃ were prepared by solid state reaction and the optical properties were investigated. The results show that the near-infrared emission of Nd³⁺ ions is significantly enhanced by the introducing of Bi³⁺ in co-doped samples. An efficient energy transfer from Bi³⁺ to Nd³⁺ corresponds to the near-infrared emission enhancement. The energy transfer efficiency reaches 64.1% for the sample with the strongest near-infrared emission, which has the optimized doping concentrations of 0.5% for Bi³⁺ and 2% for Nd³⁺. The interesting optical properties make Bi³⁺,Nd³⁺ co-doped Gd₂O₃ promising as the luminescent down-conversion layers in front of c-Si solar cells to enhance the performance of the solar cells.     

Influence of Ga2O3 addition on transparent conductive oxide films of In2O3-ZnO

Influence of incorporation of Ga in amorphous In-Zn-O transparent conductive oxide films was investigated as a function of Zn/(Zn + In). For In-Zn-O films with no Ga₂O₃, the range of Zn/(Zn + In) ratio where the amorphous phase appears became narrow at a substrate temperature of 250 °C. With increasing Ga₂O₃ quantity, amorphous films were obtained even at a high substrate temperature of 250 °C in a wider range of Zn/(Zn + In) than that of In-Zn-O films with no Ga₂O₃. This means that the trend of crystallization at higher substrate temperature was disturbed with additional Ga incorporation. For the film deposited from ZnO:Ga (Ga₂O₃: 4.5-7.5 wt%) and In₂O₃ targets, we obtained a resistivity of 2.8 × 10⁻⁴ Ω cm, nearly the same value as that for an In-Zn-O film with no Ga₂O₃. The addition of more than 7.5 wt% Ga₂O₃ induced a widening of the optical band gap.     

Growth of crystalline HgCr2S4 thin films at mild reaction conditions

Thin films of crystalline HgCr₂S₄ have been deposited on glass substrates at low temperature as low as 65 °C using a chemical bath deposition method. Typical thickness of the deposited HgCr₂S₄ thin films was 264 nm.The films were composed of closely packed irregular grains of 165-175 nm in diameter. The X-ray diffraction analysis and the selected area electron diffraction analysis revealed the deposited thin films were polycrystalline with highly (2 2 0) preferential orientation. The films exhibit a pure faint black. Their direct band gap energy was 2.39 eV with room temperature electrical resistivity of the order of 10⁻³ Ω cm.     

Electrochemical preparation and characterization of three-dimensional nanostructured Sn2S3 semiconductor films with nanorod network

Three-dimensional (3D) nanostructured Sn₂S₃ semiconductor films have been prepared on ITO-coated glass substrates by potentiostatic electrodeposition at −0.80 V (vs. SCE) from a novel plating bath containing K₄P₂O₃ as a complexing agent and Na₂SO₃ as a stabilizing agent and by subsequent annealing. Results showed that the annealing drove the as-deposited Sn₂S₃ films to grow from a granular structure into a nanorod network structure. The nanorods were around 50-100 nm in diameter and 1000 nm in length. The band gap of the annealed film was 1.65 eV and the conductivity was n type. The carrier mobility achieved up to 20.5 cm² V⁻¹ s⁻¹ due to the direct electrical pathways provided by the nanorod network.     

Thin film preparation and characterization of wide band gap Cu3TaQ4 (Q = S or Se) p-type semiconductors

The structural, optical, and electronic properties of thin films of a family of wide band gap (E_g > 2.3 eV) p-type semiconductors Cu₃TaQ₄ (Q = S or Se) are presented. Thin films prepared by pulsed laser deposition of ceramic Cu₃TaQ₄ targets and ex-situ annealing of the as-deposited films in chalcogenide vapor exhibit mixed polycrystalline/[100]-directed growth on amorphous SiO₂ substrates and strong (100) preferential orientation on single-crystal yttria-stabilized zirconia substrates. Cu₃TaS₄ (E_g = 2.70 eV) thin films are transparent over the entire visible spectrum while Cu₃TaSe₄ (E_g = 2.35 eV) thin films show some absorption in the blue. Thin film solid solutions of Cu₃TaSe_4 − xS_x and Cu₃TaSe_4 − xTe_x can be prepared by annealing Cu₃TaSe₄ films in a mixed chalcogenide vapor. Powders and thin films of Cu₃TaS₄ exhibit visible photoluminescence when illuminated by UV light.     

等离子体电解氧化法制备多孔TiO2/V2O5复合物膜层及其增强光催化产氢活性

较差的光催化产氢效率极大地阻碍了TiO₂光催化剂的工业化应用。为此,本文在含有NH₄VO₃的磷酸盐溶液中,采用等离子体电解氧化(PEO)法制备了多孔TiO₂/V₂O₅复合膜光催化剂,通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)、X射线光电子谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)对其组成、结构及光吸收性质进行了表征,并采用气相色谱评价了薄膜催化剂的光催化产氢性能,研究了电解液中NH₄VO₃含量对膜的结构、组成和光催化产氢性能的影响。结果表明:复合膜催化剂主要由锐钛矿和金红石型TiO₂组成,具有微孔结构,V₂O₅主要以无定形形式存在于膜中,与TiO₂有很强的相互作用,影响TiO₂的晶面间距。研究发现,元素V抑制了TiO₂的结晶和金红石型TiO₂的形成,扩大了薄膜的光学吸收范围。针对Na₂S+ Na₂SO₃溶液中的光催化产氢性能的研究显示,在质量浓度为1 g/L NH₄VO₃的电解液中制备的TiO₂/V₂O₅薄膜的光催化活性最高,优于近年来报道的其他光催化剂。光催化重复实验表明,该复合膜催化剂具有较高的稳定性和较为恒定的光催化活性。     

Growth and structure characterization of epitaxial Bi2Sr2Co2Oy thermoelectric thin films on LaAlO3 (001)

Epitaxial Bi₂Sr₂Co₂O_y thin films with excellent c-axis and ab-plane alignments have been grown on (001) LaAlO₃ substrates by chemical solution deposition using metal acetates as starting materials. Microstructure studies show that the resulting Bi₂Sr₂Co₂O_y films have a well-ordered layer structure with a flat and clear interface with the substrate. Scanning electron microscopy of the films reveals a step-terrace surface structure without any microcracks and pores. At room temperature, the epitaxial Bi₂Sr₂Co₂O_y films exhibit a resistivity of about 2 mΩ cm and a seebeck coefficient of about 115 μV/K comparable to those of single crystals.     

Observation of broadband infrared luminescence in a novel Bi-doped P2O5-B2O3-Al2O3 glass

A novel Bi-doped P₂O₅-B₂O₃-Al₂O₃ glass was investigated, and strong broadband NIR (near infrared) luminescence was observed when the sample was excited by 445 nm, 532 nm, 808 nm and 980 nm lasers, respectively. The max FWHM with 312 nm, the lifetime with 580 μs and the σ_emτ product with 5.3 × 10^− 24 cm² s were obtained which indicates that this glass is a promising material for broadband optical amplifier and tunable laser. The effect of the introduction of B₂O₃ on the glass structure and Bi-ions illuminant mechanism were discussed and analyzed. It is suggested that the introduction of B₂O₃ makes the glass structure closer, and the broadband NIR emission derives from Bi⁰:²D_3/2 → ⁴S_3/2 and Bi⁺:³P₁ → ³P₀ transitions.     

The effect of stress on the dielectric constants of Bi4Ti3O12 films

Both experiment and theory have shown that the stress has a notable impact on the polarization of Nd-doped Bi₄Ti₃O₁₂ films. In this paper, thermodynamic theory is used to study the effect of stress on the dielectric constants of Bi₄Ti₃O₁₂ films at room temperature with a two-dimensional model. Results indicate that the change of the dielectric constant for a-phase induced by the lattice distortion is far greater than that for c-phase. Considering the domain reorientation, the external tensile stress may lead to an obvious decrease in the effective dielectric constant of Bi₄Ti₃O₁₂ films.     

Properties of La-substituted Na0.5Bi4.5Ti4O15 ferroelectric thin films

Ferroelectric Na_0.5La_0.5Bi₄Ti₄O₁₅ (NaLaBTi) thin films were prepared by a chemical solution deposition method. The NaLaBTi thin films annealed at 750 °C under oxygen atmosphere were randomly oriented polycrystalline. Electrical properties of the NaLaBTi thin films were compared to Na_0.5Bi_4.5Ti₄O₁₅ thin films and better properties were observed in the NaLaBTi thin films. Remnant polarization (2P_r) and coercive electric field (2E_c) were 43 µC/cm² and 204 kV/cm at an applied electric field of 478 kV/cm, respectively. Leakage current density was 1.95 × 10^− 6 A/cm² at 100 kV/cm. Dielectric constant and dielectric loss were 805 and 0.05 at 1 kHz, respectively. Switchable polarization was suppressed by 15% after 1.44 × 10¹⁰ switching cycles.     

Structure, morphology and optical properties of nanocrystalline yttrium oxide (Y2O3) thin films

Yttrium oxide (Y₂O₃) thin films were grown onto Si(1 0 0) substrates using reactive magnetron sputter-deposition at temperatures ranging from room temperature (RT) to 500 °C. The effect of growth temperature (T_s) on the growth behavior, microstructure and optical properties of Y₂O₃ films was investigated. The structural studies employing reflection high-energy electron diffraction RHEED indicate that the films grown at room temperature (RT) are amorphous while the films grown at T_s = 300-500 °C are nanocrystalline and crystallize in cubic structure. Grain-size (L) increases from ∼15 to 40 nm with increasing T_s. Spectroscopic ellipsometry measurements indicate that the size-effects and ultra-microstructure were significant on the optical constants and their dispersion profiles of Y₂O₃ films. A significant enhancement in the index of refraction (n) (from 2.03 to 2.25) is observed in well-defined Y₂O₃ nanocrystalline films compared to that of amorphous Y₂O₃. The observed changes in the optical constants were explained on the basis of increased packing density and crystallinity of the films with increasing T_s. The spectrophotometry analysis indicates the direct nature of the band gap (E_g) in Y₂O₃ films. E_g values vary in the range of 5.91-6.15 eV for Y₂O₃ films grown in the range of RT-500 °C, where the lower E_g values for films grown at lower temperature is attributed to incomplete oxidation and formation of chemical defects. A direct, linear relationship between microstructure and optical parameters found for Y₂O₃ films suggest that tuning optical properties for desired applications can be achieved by controlling the size and structure at the nanoscale dimensions.     

Preparation and photocatalytic activity of novel efficient photocatalyst Sr2Bi2O5

A novel visible-light-driven photocatalyst of Sr₂Bi₂O₅ is prepared by solid-state reaction at 780 °C. The optical band gap of Sr₂Bi₂O₅ is determined to be 2.87 eV by UV-Vis diffuse reflectance spectroscopy. Under both UV and visible-light irradiation, the photocatalytic activity for degrading methyl orange (MO) over Sr₂Bi₂O₅ is higher than those over BiVO₄, and SrBi₂O₄. The relationships between the photocatalytic properties of Sr₂Bi₂O₅, SrBi₂O₄, and BiVO₄ and their crystal structures are discussed. Among Sr₂Bi₂O₅, SrBi₂O₄, and BiVO₄, the higher photocatalytic activity of Sr₂Bi₂O₅ is ascribed to its higher level of distortion of the metal-oxygen polyhedra, and the lower packing factor degree.