Wenfeng Qin

Enhanced dielectric characteristics of preferential (1 1 1)-oriented BZT thin films by manganese doping

Ba(Zr0.2Ti0.8)O3 (BZT) and 2 mol% Mn additional doped BZT (Mn–BZT) thin films were deposited on Pt/Ti/SiO2/Si by the pulsed laser deposition (PLD) technique under the same growth conditions. X-ray diffraction scans showed that both films were polycrystalline and preferentially (1 1 1)-oriented, and an enhanced crystallization effect was obtained after Mn doping. The parallel-plate capacitors of Au/BZT/Pt and Au/Mn–BZT/Pt were prepared to investigate the electric properties, respectively. The remanent polarization and the coercive electric field for Mn-doped BZT film were both smaller than those of undoped BZT film. Furthermore, Mn-doped BZT film exhibited a higher dielectric constant of 460 at zero bias, larger dielectric tunability of 69.0% and lower dielectric loss of 5.0‰ under an applied electric field of 615 kV cm−1 than those of undoped BZT film. The figure of merit for preferentially (1 1 1)-oriented BZT thin film was greatly enhanced from 94 to 138 by Mn doping. The enhanced dielectric behaviour by Mn doping could be mainly attributed to the decrease in electron concentration and oxygen vacancies and the reorientation of the defect complex.

A novel process for CeO2 single buffer layer on biaxially textured metal substrates in YBCO coated conductors

We report a newly developed method, namely the in situ postannealing texture (IPAT) technique, based on a two-step principle to fabricate CeO2 single buffer layer on biaxially textured Ni–5 at.%W substrate by a reactive direct-current sputtering method. The annealing temperature and time dependence of the grain alignment in CeO2 buffer layers was studied. High-quality CeO2 layers were achieved at annealing temperatures from 750 to 850 °C, with annealing times from 10 to 20 min. Atomic force microscopy revealed, via the novel IPAT method, a continuous, dense, and crack-free surface morphology for CeO2 thin films with a thickness of up to 300 nm, which act as a sufficiently good single buffer for YBa2Cu3O7−δ (YBCO) coated conductors (CCs). The preparation of subsequent YBCO CCs grown on the IPAT-prepared CeO2 single buffer layers was also investigated.

Enhanced Dielectric Characteristics Of Manganese-Doped Bzt Thin Films

Ba(Zr0.2Ti0.8)O3 (BZT) and 2 mol% Mn additional doped BZT (Mn-BZT) thin films were deposited by pulsed laser deposition technique under the same growth conditions on LaAlO3 substrates with the bottom electrodes of LaNiO3. The microstructure of the films was characterized by X-ray diffraction (XRD) in the mode of θ–2θ scan and Φ-scan. The results indicated that BZT film was (001)-oriented_with an in-plane relationship of BZT[100]//LNO[100]//LAO[100]. The Mn-BZT film exhibited higher dielectric constant of 225 at zero electric field, larger dielectric tunability of 59.4%, and lower dielectric loss of 1.8% under an applied electric field of 720 kV/cm. The figure of merit for BZT thin film increased from 19.8 to 33 by Mn doping. The enhanced dielectric behavior by Mn doping could be mainly attributed to the decrease of oxygen vacancies and the reorientation of the dipolar defect complex of

Preparation and characterization of microcrack-free thick YBa2Cu3O7-δ films

{\rm Mn}^{\prime\prime}_{\rm Ti} - {\rm V}_{\ddot{\rm O}}

Reel-to-reel continuous deposition of CexZr1-xO2 single buffer layer for YBCO coated conductors

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DIELECTRIC CHARACTERISTICS OF BST/BZT/BST MULTILAYER

Abstract High quality epitaxial YBa 2 Cu 3 O 7-δ (YBCO) superconducting films were fabricated on (OO l ) LaAlO 3 substrates using the direct-current sputtering method. The attainment of an unusually high film thickness (up to 2.0 um) without microcracking was attributed in part to the presence of pores correlated with yttrium-rich composition in the films. The influence of the film thickness on the microstructure was investigated by X-ray diffraction conventional scan (θ-2θ, ω-scan, pole figure) and high-resolution reciprocal space mapping. The films were c -axis oriented with no a -axis-oriented grains up to the thickness of 2 μm. The surface morphology and the critical current density ( J c ) strongly depended on the film thickness. Furthermore, the reasons for these thickness dependences were elucidated in detail.

The structure and dielectrics of epitaxially strained BaRO3(R=Ti, Zr) thin films

In this paper, a study regarding the epitaxial growth of CexZr1-xO2 film on biaxially textured Ni-5at.%W substrate and its use as a single buffer layer of a YBCO coated conductors was reported. Films of Ce-Zr mixed oxide were prepared by direct-current (d.c.) reactive magnetron sputtering with the two sputtering guns arranged symmetrically with respect to the substrate. In sputtering process, d.c. power of Zr was fixed in 200 W while that of Ce was varied with 30 W, 50 W, 75 W, and 100 W, respectively. It was confirmed that the composition of the films could be controlled with modulating power of Ce target. All samples exhibited good epitaxial growth with c-axis perpendicular to the substrate surface. Atomic force microscope revealed a continuous, dense, and crack-free surface morphology for Ce0.32Zr0.68O2 thin films, which provided themselves as the good single buffer to the YBa2Cu3O7-δ (YBCO) coated conductors. High quality Ce0.32Zr0.68O2 buffer layers up to 100-m length could be fabricated with production speed of about 1.2m/h. X-ray scans have been performed as a function of length to determine the crystallographic consistency of the epitaxial Ce0.32Zr0.68O2 over length.

Epitaxial growth and electrical properties of Ba0.6Sr0.4TiO3 thin films with conductive La0.5Sr0.5CoO3 bottom electrodes

Ba0.6Sr0.4TiO3 (BST) and Ba0.6Sr0.4TiO3/Ba(Zr0.2Ti0.8)O3/Ba0.6Sr0.4TiO3 (BST/BZT/BST) multilayer (ML) films were prepared by pulsed laser deposition on the LaNiO3-coated LaAlO3 substrate. X-ray diffraction analysis revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases and atomic force microscopy showed that the grain size of ML films was similar to BST films in size. The dielectric properties of the BST and ML thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the dielectric tunability for ML films slightly decreased, while the loss decreased synchronously. The figure-of-merit factor value increases from 17.32 for BST films to 42.14 for ML films under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a positive bias field of 300 kV/cm decreases from 3.76 × 10-6 to 1.25 × 10-7 A/cm2 for ML films. This work clearly reveals the highly promising potential of BST/BZT/BST multilayer films compared with BST films for application in tunable microwave devices.

Simultaneous double-sided deposition of long-length epitaxial CeO2 buffer layers for YBCO coated conductors

The structure and static dielectric permittivity of BaRO3(R=Ti, Zr) thin films as a function of epitaxial strain are determined by using first-principle density functional theory calculation based on pseudopotentials and a plane-wave basis. It is found that BaTiO3 thin films under compressive misfit strain can be grown more easily than those under tensile misfit strain, while thin films of BaZrO3 can be grown more easily under tensile strain. The static dielectric permittivity of BaTiO3 thin films under different misfit strain is obtained by calculating optical phonon frequencies and Born effective charges using density functional perturbation theory. The zero-temperature dielectric permittivity of ε33 increases to the maximal value under compressive misfit strain, while the ε11/22 reaches to its maximal value under tensile misfit strain. For BaZrO3 thin films, the dielectric permittivity εr changes little. However, εr exhibits non-linear characteristics under tensile strain, which reaches to the maximal value under misfit strain of ~1%. This unsymmetrical dielectric behavior caused by strain is attributed to soften phonons in BaTiO3 or BaZrO3 thin films.

Reel-to-reel continuous simultaneous double-sided deposition of highly textured CeO2 templates for YBa2Cu3O7−δ coated conductors

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). X-ray diffraction θ~2θ and Φ scan showed that the epitaxial relationship of BST /LSCO /LAO was [001] BST//[001] LSCO//[001] LAO. The atomic force microscope (AFM) revealed a smooth and crack-free surface of BST films on LSCO-coated LAO substrate with the average grain size of 120 nm and the RMS of 1.564nm for BST films. Pt/BST/LSCO capacitor was fabricated to perform Capacitance-Voltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.63×10-7 A/cm2 under an applied filed of 200 kV/cm.