| Pyrochlore oxides constitute a large family of transition metal (TM) oxides like perovskites. They have the general chemical formula A2B2O7 or A2B2O6O’, where A is a larger cation and B is a smaller TM cation. It is known that the pyrochlore structure sometimes tolerates vacancies at the A and O’ sites. Such pyrochlore oxides are generally called defect pyrochlores. Recently, we have discovered new superconductors, KOs2O6 and RbOs2O6. They should not be classified as defect pyrochlores, because of apparent difference in the metal occupations. Thus, we call this AB2O6 type oxide a beta-pyrochlore oxide to discriminate it from ordinary defect pyrochlore oxides. |
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