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MgB2 samples doped with TiO2 nanoparticles were prepared and the effect of TiO2 addition on the superconducting transition temperature (Tc), irreversibility field (Hirr) and critical current density (Jc) were investigated. It is found that the hexagonal lattice parameters a and c decrease with TiO2 doping. Tc decreases gradually from 38.2 to 37.8 K as the TiO2 content increases from 0 to 15 wt%. The Hirr increases at 20 K from 4.3 to 4.9 T as the TiO2 content increases from 0 to 10 wt%, and at the same temperature Jc increases from 450 to 4250 A/cm2 at 4.2 T. [Copyright &y& Elsevier]

A series of polycrystalline samples of Mg1−x(Zn0.5Al0.5)xB2 (0⩽x⩽0.8) were prepared by solid state reaction method and their structure, superconducting transition temperature (Tc) and transport properties were investigated by means of X-ray diffraction (XRD), ac susceptibility, magnetization and resistivity. The double doping leads to decreases in both the lattice parameters a and c, and the Tc decreases with increasing dopant content. A systematical comparison with Al doped- and Li, Al double doped MgB2 of structure, superconducting transition and critical current density (Jc) is made. It is suggested that the chemical pressure effect plays a more important role influencing the normal state transport and Tc than the change of carrier concentration, and the introduction of disorder into the Mg layers shows little influence improving the irreversibility field and Jc. [Copyright &y& Elsevier]

A series of polycrystalline samples of Mg1−x(Al0.5Li0.5)xB2 (0⩽x⩽0.6) were prepared by a solid state reaction method and their structure, superconducting transition temperature and magneto-transport properties were investigated by means of X-ray diffraction (XRD), ac-susceptibility and resistance in varied magnetic fields. The double doping leads to decreases in both the lattice parameters a and c. The superconducting transition temperature (Tc) decreases with double doping, but the Tc is systematically higher than that of the single Al-doped samples. It is suggested that the hole band filling has little effect on Tc at high doping level, while the disorder induced by doping plays an important role in suppressing Tc. A systematic comparison with Al-doped MgB2 of the structure, superconducting transition and irreversibility field is made. [Copyright &y& Elsevier]