The crystal growth of (VO)(2)P2O7 single crystals is discussed with respect
to the formation of a high-temperature nonstoichiometric phase (VO)(2)P2O7
+x. The interaction between vanadyl pyrophosphate and oxygen was investigat
ed in the temperature region 600-900 degreesC. It was found that the decay
of the high-temperature nonstoichiometric phase at lower temperature led to
imperfections in crystals grown in an atmosphere with oxygen concentration
higher than 0.2%. Two mechanisms for the decay are considered. The oxygen
content of the crystals may be reduced at the surface by evolution of gaseo
us oxygen, whereas in the bulk the formation of an oxygen-enriched solid ph
ase is observed. (C) 2000 Elsevier Science Ltd. All rights reserved.