High-Pressure Synthesis Of The Cobalt Pyrochlore Oxide Pb2co2o7 With Large Cation Mixed Occupancy

The novel A(2)B(4)O(7)-type compound Pb2Co2O7 was synthesized at 8 GPa and 1673 K. Synchrotron X-ray diffraction shows a cubic pyrochlore structure with space group Fd (3) over barm. Rietveld structural analysis reveals a large cation mixed occupancy at both A and B sites by about 40%, the greatest value found in the pyrochlore family. In combination with the X-ray absorption spectroscopy results, the specific chemical composition and charge states are determined to be (Co0.6Pb0.4)(3+)(2)(Pb0.6Co0.4)O-4+(2)7 in which both the A-site Co3+ and the B-site Co4+ are low-spin. Due to the tetrahedral geometric frustration effects as well as the random Co4+ and Pb4+ distribution at the B site, spin glassy behavior is well observed following the conventional critical slowing down feature in Pb2Co2O7.