Zur Frage nach der Existenz eines kubischen Pyrochlors Pb2Sb2O7

On the Problem of the Existence of a Cubic Pyrochlore Pb₂Sb₂O₇ The reaction of PbO, PbO₂, PbCO₃ or Pb(CH₃CO₂)₂ · 3 H₂O with Sb₂O₃ (ratio 2:1 Mol.) gives up to 700°C a cubic pyrochlore together with PbSb₂O₆. The pyrochlore contains Pb(IV) and has the approximate composition Pb[PbSb]O_6,75 with a = 1066–1069 pm. After heating up to 900°C rhombohedral Pb₂Sb₂O₇ is formed. There is no evidence for the existence of a cubic Pb₂Sb₂O₇ with Pyrochlore structure.