Presentation Information
[WBP1-09]Effect of BaHfO3 Concentration on the Microstructure of YBa2Cu3O7-x Thin Films
*Nao Ikemoto1, Haruna Nogami1, Manabu Ishimaru1, Shin Okumura2, Tomoya Horide2, Yutaka Yoshida2 (1. Kyushu Institute of Technology (Japan), 2. Nagoya University (Japan))
Keywords:
YBa2Cu3O7-x(YBCO),BaHfO3 (BHO) nanorods,transmission electron microscopy (TEM)
Non-superconducting inclusions in YBa2Cu3O7-x (YBCO) films act as effective flux pinning centers that increase the critical current density (Jc). Among such inclusions, BaMO3-type compounds (M = Sn, Hf, Zr) with a perovskite structure spontaneously form nanorods during film growth and contribute significantly to the improvement of Jc, especially under magnetic fields aligned parallel to the c-axis. While the amount of BaMO3 added has been shown to influence the resulting microstructure and flux pinning performance, the detailed impact of BaHfO3 (BHO) content on the nanostructure of thick YBCO films remains inadequately studied. Notably, thick YBCO films are advantageous in practical applications due to their suppressed Jc degradation, making it essential to understand how to optimize their nanostructure. This study investigates how different BHO concentrations affect the nanostructural and morphological characteristics of YBCO films.
YBCO films with 3% and 7% BHO were fabricated on (001)-oriented SrTiO3 single-crystal substrates using pulsed laser deposition (PLD) at 900 ℃ in an oxygen atmosphere of 400 mTorr, with a repetition rate of 5 Hz. Cross-sectional and plan-view samples were prepared using a focused ion beam or ion milling. The structural properties and elemental distribution of the films were analyzed using transmission electron microscopy (TEM) and scanning TEM (STEM).
Cross-sectional bright-field TEM images revealed that the 3% BHO-added film contained long and continuous nanorods extending from the substrate to the surface. Selected area electron diffraction patterns confirmed the coexistence of YBCO and BHO phases. In contrast, the 7% BHO-added film showed thicker nanorods with discontinuous growth. The nanorods in this film exhibited diameter variation along the growth direction, becoming thicker near the film surface. Based on wide-area observations, both the thin film were found to contain uniformly distributed nanorods and large precipitates. The average size of these precipitates was approximately 40 nm for the 3% BHO-added film and about 70 nm for the 7% film.
Plan-view high-angular datk-field STEM images further revealed nanorod distributions and inhomogeneous regions. The inhomogeneous structures were approximately 200 nm in the 3% film and increased to around 400 nm in the 7% film. Moreover, the density of nanorods was found to be significantly higher in the 7% BHO-added film, indicating that the BHO concentration strongly influences nanorod formation behavior, including continuity, morphology, and spatial distribution.
These findings demonstrate that increasing the BHO content results in distinct changes to nanostructure and morphology, including increased rod diameter, discontinuity, and higher density. We will also report on the elemental distribution in the obtained thin films.
YBCO films with 3% and 7% BHO were fabricated on (001)-oriented SrTiO3 single-crystal substrates using pulsed laser deposition (PLD) at 900 ℃ in an oxygen atmosphere of 400 mTorr, with a repetition rate of 5 Hz. Cross-sectional and plan-view samples were prepared using a focused ion beam or ion milling. The structural properties and elemental distribution of the films were analyzed using transmission electron microscopy (TEM) and scanning TEM (STEM).
Cross-sectional bright-field TEM images revealed that the 3% BHO-added film contained long and continuous nanorods extending from the substrate to the surface. Selected area electron diffraction patterns confirmed the coexistence of YBCO and BHO phases. In contrast, the 7% BHO-added film showed thicker nanorods with discontinuous growth. The nanorods in this film exhibited diameter variation along the growth direction, becoming thicker near the film surface. Based on wide-area observations, both the thin film were found to contain uniformly distributed nanorods and large precipitates. The average size of these precipitates was approximately 40 nm for the 3% BHO-added film and about 70 nm for the 7% film.
Plan-view high-angular datk-field STEM images further revealed nanorod distributions and inhomogeneous regions. The inhomogeneous structures were approximately 200 nm in the 3% film and increased to around 400 nm in the 7% film. Moreover, the density of nanorods was found to be significantly higher in the 7% BHO-added film, indicating that the BHO concentration strongly influences nanorod formation behavior, including continuity, morphology, and spatial distribution.
These findings demonstrate that increasing the BHO content results in distinct changes to nanostructure and morphology, including increased rod diameter, discontinuity, and higher density. We will also report on the elemental distribution in the obtained thin films.