| http://www.w3.org/ns/prov#value | - In addition to YBa2Cu3O7-x, material of the class RBa2Cu3O7-x, where R is a lanthanide element other than lanthanum, cerium, praseodymium, promethium or terbium, is also satisfactory, as are the superconductive bismuth-strontium-calcium-copper-oxygen compounds and the superconductive thallium-barium-calcium-copper-oxygen compounds.
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