Improvement of critical current density in MgB2 superconductors by Zr doping at ambient pressure

We present the superconducting properties and phase compositions of Mg1-xZrxB2 bulk samples fabricated by a solid-state reaction at ambient pressure. It is found that a small amount of Zr atoms may be introduced into the lattice of MgB2, while the majority of them forms ZrB2 phase. The Mg0.9Zr0.1B2 sample shows the highest J(C) of 2.1x10(6) A/cm(2) in 0.56 T at 5 K and 1.83x10(6) A/cm(2) in self-field at 20 K, higher irreversibility field and larger upper critical field in MgB2 bulk samples. The combination of good grain connection, the reduction of grain size and small ZrB2 particles in the sample may be responsible for the significant enhancement of J(C) in Zr-doped samples. This technique has a great potential to prepare high performance MgB2 bulk samples and wires on an industrial scale. (C) 2001 American Institute of Physics.