Synthesis, crystal structure, and superconductivity of Ba(Bi0.25Pb0.75)1−xMgxO3−δ

Abstract

Magnesium has been doped into the B-site of BaBi0.25Pb0.75O3−δ to form a solid solution Ba(Bi0.25Pb0.75)1−xMgxO3−δ (0 ≤ x ≤ 0.10) by solid-state reaction. The X-ray, neutron, and selected area electron diffraction are used to confirm that this solid solution crystallizes in triclinic space group P1. The unit cell volume of Ba(Bi0.25Pb0.75)1−xMgxO3−δ increases with Mg, which is surprising because the radius of Mg2+ is smaller than any radius of Bi3+, Bi5+, Pb2+, and Pb4+. XPS and iodometric titration data of samples show that the oxygen vacancies increase with Mg in Ba(Bi0.25Pb0.75)1−xMgxO3−δ. The increased oxygen vacancies result in increase of Bi3+:Bi5+ and Pb2+:Pb4+ ratios, which is the utmost possible reason for unit cell volume increase. They are all superconductors with TCzero (the highest temperature at which the electrical resistivity becomes “zero”) between 11.2 and 9.2 K.