An uncommon phenomenon has been detected during the pyrolysis of the previously described |K 1.14Bi 3+ 0.37□ 0.49||Bi 3+ 0.27Bi 5+ 1.73||O 5.71OH 0.29||H 2O| 0.82 pyrochlore. The pyrochlore structure is retained but changes continuously. An X-Ray powder diffraction study of a partially decomposed sample reveals that the change can only be interpreted as a migration of Bi 3+ ions from 16c to 16d sites, with a corresponding appearance of vacancies in the octahedral subarray of the pyrochlore structure.