Ultrasonic synthesis of MgB 2 superconducting nanocomposites

1. Ultrasonic synthesis of MgB2 superconducting nanocomposites Rusian Prozorov, Iowa State University, DMR 0603841 We have demonstrated that powerful ultrasonic irradiation (sonication) of the brittle superconductors in a slurry with metallo-organic liquid results in nanocomposite material with enhanced pinning properties. High-Tc ceramics [1] and MgB2 were studied [2]. Analysis showed that in case of magnetic pinning centers, in addition to the core pinning, long-range magnetic pinning plays important role and leads to enhancement of magnetic irreversibility [2,3]. Our new study is to determine the effect of sonication on the precursors (Mg and B) with and without various additions to enhance critical current densities. Major attention is given to the purity and isotope content of boron. Additionally, the sonicated powders were subject to hot isostatic pressure (HIP) to synthesise MgB2 superconductor. It was found that sonication of the pre-cursors significantly improves connectivity of the resulting material [4]. Currently we work on synthesis of the nanocomposites using this new sonochemical route. Figure 1. Positive effect of sonication on 95% boron + MgB2 powder with subsequent HIP synthesis Figure 2. Scanning Electron Microscope images of the samples used in Fig.1. Note much smoother structure of the pre-sonicated material. [1] Appl. Phys. Lett. 85, 3513 (2004) [2] Appl. Phys. Lett., 83, 2019 (2003). [3] Phys. Rev. B 71, 024527 (2005) [4] manuscript in preparation

2. Ultrasonic synthesis of MgB2 superconducting nanocomposites Rusian Prozorov, Iowa State University, DMR 0603841 The project entailed training four students, one graduate1 and three undergraduate students2. Students performed all steps of the synthesis, measurements and data analysis under the supervision of Ruslan Prozorov. The activities included training and work with Scanning Electron Microscope; performing magnetic measurements on standard and home-built susceptometers; construction of an AC susceptometer; using magneto-optical imaging to study flux distribution in the obtained materials. In addition, several groups of perspective students have visited the laboratory and some later decided to engage in this research project. Latest results of this study were presented at the APS March Meeting 2007 Conference in Denver by a graduate student, Brett McCarty. Direct immersion horn in sonication cell with Ar gas flow Hot isostatic pressure apparatus