Composites of MgB2 with Bi2O3, Bi, Sb2O3, or Sb Obtained by Ex-situ Spark Plasma Sintering

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Mixtures of MgB2 and metal or oxide additions with starting compositions of (MgB2)(M2O3)x, x = 0.0025, 0.005, 0.015, and (MgB2)(M)y, y = 0.01, M = Bi, Sb, were processed by spark plasma sintering (SPS). As-obtained samples are composites with high density exceeding 94% of the theoretical values. Secondary phases indicate similar reactions for samples with Bi- or Sb-based additions. However, samples show very different superconducting characteristics depending on the addition type and amount. A direct correlation with the melting temperature of the addition could not be revealed, although some aspects will be discussed. From the critical current density (J_{\text{c}}) and irreversibility field (H_{\text{irr}}) enhancement viewpoints, optimum additions are oxides for x=0.0025, 0.005. Both oxides improve J_{\text{c}} at high fields, but Sb2O3 is effective up to 10 K, whereas Bi2O3 is effective up to 30 K. Metal additions decrease J_{\text{c}} and H_{\text{irr}} when compared with a pristine MgB2 sample.
2012-11-25