So far, two families of crystal structures exhibit superconductivity. The first family, with tc around 40-50 k, is typified by la2xbaxcuo4-z, which has nominal cu oxidization number con = 2+x-2z; the second family has tc = 90-100k and is typified by yba2cu3o7-z, with con = 2.333-0.666Z. In both families, there are planar, or almost planar ("dimpled"), arrays of cu and o atoms of stoichiometry cuo2, surmounted by apical o atoms, yielding a square- pyramidal (i.e., distorted octahedral) coordination about cu; these are the "2-d planes," possibly responsible for tc around 40 k. In the yba2cu3o7-z structure, there is also a ribbon motif of square- planar cu and o atoms of stoichiometry cuo3; this "1-d ribbon" may be responsible for tc around 90 k. The present authors first achieved superconductivity in a rapid-quenched green-black composite gd3ba3cu4oz, with tc=62k (onset at 71k), and have also found superconductivity in single-phase yba2cu3o7-z, with tc=90k (onset at 96k). The present paper reports on the synthesis, powder x-ray diffraction, and conductivity of gdba2cu3ox, in which tc=100 k (onset at 108 k).
Ch 26 High-temp. Superconducting Materials: Prep, Properties & Proc; Dekker, 1988, PP. 327-333