Refinement of Nb3Sn grain size by the generation of ZrO2 precipitates in   Nb3Sn wires
  In this letter we demonstrate that if oxygen can be properly supplied to (Nb-Zr)-Sn wires, ZrO2 precipitates will form during the heat treatment, refining the Nb3Sn grain size markedly. Here, a Nb3Sn subelement was fabricated in which Nb-1Zr alloy was used, and oxygen was supplied via SnO2 powder. The results showed that such a design could supply sufficient oxygen to internally oxidize the Zr in the Nb-1Zr alloy, and that the sample reacted at 650 {\deg}C had grain sizes of ~45 nm, less than half the size of the grains in present Nb3Sn conductors. Magnetic measurements showed that the peak of the pinning force vs. field (Fp-B) curve was shifted to ~0.3Birr (the irreversibility field). 
X. Xu, M. Sumption, X. Peng, and E. W. Collings
cond-mat.supr-con cond-mat.mtrl-sci