Gaoyang Zhao

An advanced low-fluorine solution route for fabrication of high-performance YBCO superconducting films

We have developed a new low-fluorine solution consisting of non-fluorine (F-free) barium and copper salts, and fluorine-containing yttrium trifluoroacetate. Using this new low-fluorine solution, the BaCO3 phase was avoided in the pyrolyzed precursor films. Instead, CuO, Y and Ba fluorides (YF3 and BaF2) were formed in the precursor films pyrolyzed at 450??C, which was the same as when an All-TFA solution (prepared using Y, Ba, Cu trifluoroacetates as precursors) or other fluorine-reduced solutions were used. This new kind of low-fluorine solution has only 23% of the fluorine content in an All-TFA solution, and the fluorine content was lower than any other fluorine-reduced solution. Thus, rapid production of YBa2Cu3O7?x (YBCO) films can be easily realized. Using a heating rate of 10??C?min?1 in the pyrolysis process, a high critical current density (Jc) of 5?MA?cm?2 (at 77?K, 0?T) was obtained in YBCO films fabricated on LaAlO3 (LAO) single crystal substrates from the new starting solution.

Sol-gel preparation of La-doped bismuth ferrite thin film and its low-temperature ferromagnetic and ferroelectric properties

Abstract Bi 0.85 La 0.15 FeO 3 thin film was prepared on ATO glass substrates by sol-gel technique. The effect of La doping on phase structure, film surface quality, ion valence, and ferroelectric/magnetic properties of Bi 0.85 La 0.15 FeO 3 film were investigated. La doping suppressed the formation of impurity phases and the transition of Fe 3+ to Fe 2+ ions at room temperature. Compared with the un-doped BiFeO 3 , La-doping also increased the average grain size and the film density, which resulted in the decrease of film leakage current density. The remanent polarization and saturation magnetization were enhanced significantly by La doping. The remanent polarization of Bi 0.85 La 0.15 FeO 3 films gradually decreased while saturation magnetization increased with the decrease of measuring temperature within a range from 50 to 300 K.

All chemical solution deposition of textured YBa2Cu3O7?x/Y0.2Ce0.8O2/La2Zr2O7 multilayer films on biaxially textured NiW tape

Biaxially textured La2Zr2O7 (LZO) single buffer layer, Y0.2Ce0.8O2 (YCO) single buffer layer, and YCO/LZO bilayer buffer layer are prepared on NiW tapes using chemical solution deposition technique. All the buffer layers are of good in-plane and out-of-plane texture. The introduction of a YCO cap layer on the LZO buffer layer improves the surface quality of the films. YBa2Cu3O7−x (YBCO) films are then prepared on these buffer layers using our recently developed low-fluorine solution route. Purely c-oriented YBCO films with good in-plane and out-of-plane texture are obtained on the YCO/LZO bilayer buffer layers. The YBCO/YCO/LZO/Ni stack prepared using all chemical solution routes shows a high Tc over 90 K, a sharp transition temperature ΔT = 0.8 K, and a Jc of 0.7 MA cm−2(at 77 K, 0T).

Synthesis and characterization of photochemical sol–gel derived lanthanum doped Bi4Ti3O12 film and its micro-patterns

A unique photochemical sol–gel route was employed to prepare La-doped Bi4Ti3O12 film (BLT) using bismuth nitrate, lanthanum nitrate, and titanium tetra-n-butoxide as starting materials. Through complex reaction between benzoyl acetone and Ti4+ ions, the synthesized La-doped Bi4Ti3O12 sol and gel films exhibited photosensitivity. Micro-patterned BLT film was obtained by a photoresist-free micro-patterning technique. The phase microstructures, electrical and ferroelectric properties of the as-prepared BLT film were characterized. By doping Lanthanum, the strong (00l)-oriented BT phase was transformed to randomly-oriented orthorhombic phase, resulting in the enhanced remanent polarization and improved fatigue properties. The obtained BLT film showed good ferroelectric properties with a long fatigue cycles over 1010 cycles.

High Critical Current Density of YBa 2 Cu 3 O 7−x Superconducting Films Prepared through a DUV-assisted Solution Deposition Process

Although the solution deposition of YBa2Cu3O7−x (YBCO) superconducting films is cost effective and capable of large-scale production, further improvements in their superconductivity are necessary. In this study, a deep UV (DUV) irradiation technique combined with a low-fluorine solution process was developed to prepare YBCO films. An acrylic acidic group as the chelating agent was used in the precursor solution. The acrylic acidic group was highly sensitive to DUV light at 254 nm and significantly absorbed UV light. The coated gel films exposed to DUV light decomposed at 150 °C and copper aggregation was prevented. The UV irradiation promoted the removal of the carbon residue and other by-products in the films, increased the density and enhanced the crystallinity and superconductivity of the YBCO films. Using a solution with F/Ba = 2, YBCO films with thicknesses of 260 nm and enhanced critical current densities of nearly 8 MA/cm2 were produced on the LaAlO3 (LAO) substrates.

Nano-imprinting of surface relief gratings on soda-aluminosilicate and soda-lime silicate glasses

One-dimensional gratings of 700-nm period were imprinted on a soda-aluminosilicate glass (NAS) and a soda-lime silicate glass (NCS) using a platinum-coated SiO2 mold with application of DC voltage. The migration of network modifier cations below the anode side surface to the cathode side is a necessary condition for grating formation. Glass surfaces were chemically etched using a 55% KOH solution at 70°C. The top area of the NAS grating ridge, where the non-contacted area of the mold is located, was etched preferentially. Finally, the reverse concavo-convex grating appeared by etching. Localized stress corrosion in the grating ridge is expected to be an origin of the anisotropic etching and the grating pattern formation. In contrast, such anomalous etching behavior was not observed for the NCS. The bottom of the grating groove, the mold contacted area, was etched monotonously, maintaining the initial sinusoidal grating shape.

Proton-Driven Intercalation and Ion Substitution Utilizing Solid-State Electrochemical Reaction

The development of an unconventional synthesis method has a large potential to drastically advance materials science. In this research, a new synthesis method based on a solid-state electrochemical reaction was demonstrated, which can be made available for intercalation and ion substitution. It was referred to as proton-driven ion introduction (PDII). The protons generated by the electrolytic dissociation of hydrogen drive other monovalent cations along a high electric field in the solid state. Utilizing this mechanism, Li+, Na+, K+, Cu+, and Ag+ were intercalated into a layered TaS2 single crystal while maintaining high crystallinity. This liquid-free process of ion introduction allows the application of high voltage around several kilovolts to the sample. Such a high electric field strongly accelerates ion substitution. Actually, compared to conventional solid-state reaction, PDII introduced 15 times the amount of K into Na super ionic conductor (NASICON)-structured Na3-xKxV2(PO4)3. The obtained materials exhibited a thermodynamically metastable phase, which has not been reported so far. This concept and idea for ion introduction is expected to form new functional compounds and/or phases.