We present the superconducting properties and phase compositions of Mg 1Ϫx Zr x B 2 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 MgB 2 , while the majority of them forms ZrB 2 phase. The Mg 0.9 Zr 0.1 B 2 sample shows the highest J C of 2.1ϫ10 6 A/cm 2 in 0.56 T at 5 K and 1.83ϫ10 6 A/cm 2 in self-field at 20 K, higher irreversibility field and larger upper critical field in MgB 2 bulk samples. The combination of good grain connection, the reduction of grain size and small ZrB 2 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 MgB 2 bulk samples and wires on an industrial scale.

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Ti-doped MgB2/Cu tapes with Ta as a buffer layer were prepared through the in situ powder in tube method by using Mg, Ti, and B powders. The phase compositions, microstructure features, and superconducting properties were investigated by x-ray diffraction, scanning electron microscope, and superconducting quantum interference device magnetometer. It is found that TiB2 phase was formed in Ti-doped MgB2 tape. Magnetization measurement results show that the critical transition temperature of MgB2/Ta/Cu tape with Ti doping is around 38 K. The irreversibility field Hirr and critical current density Jc can be greatly enhanced by Ti doping. Hirr of the Mg0.9Ti0.1B2 tape is as high as 7.4 T at 10 K. The high critical current density Jc of 1.5×106 A/cm2 (10 K, self field) and 9.3×105 A/cm2 (20 K, self field) are obtained in the Mg0.9Ti0.1B2 tape. In addition, a suitable amount of Ti doping can lead to a high density and fine grain size of MgB2, which may be the reason for high Jc in Ti-doped MgB2 tapes.