Old and New Oxide Superconductors

Since the initial discovery of superconductivity in copper oxides,¹ many new oxide superconductors have been discovered. Nearly all have been based on copper and oxygen. Many thousands of papers have been published on these materials in the past four years, and their physics and chemistry have also been reviewed many times (see, for instance references 2-4). Here we present a brief review of the crystal structures and chemistry of oxide superconductors known before 1986. We argue that they represent a different class of materials than is found for copper oxides, and also bismuth/lead based oxides, which we describe briefly as well. Finally we describe some recent results on conductive oxides which do not include copper, lead, or bismuth, and also a new copper oxide superconductor with a simple double layer structure, which we believe will be of considerable interest in the future understanding of copper oxide based superconductors.