Incommensurate structures and radiation damage in Rb 2 V 3 O 8 and K 2 V 3 O 8 mixed-valence vanadate fresnoites

• Published in: Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2023-04, Vol.79 (Pt 2), p.104-113
• Main Authors: Grzechnik, Andrzej, Petříček, Vaclav, Chernyshov, Dmitry, McMonagle, Charles, Geise, Tobias, Shahed, Hend, Friese, Karen
• Format: Article
• Language: English
• ISSN: 2052-5206; 2052-5206
• DOI: 10.1107/S2052520623000999

The structures and phase transitions to incommensurate structures in Rb V O and K V O mixed-valence vanadate fresnoites are studied with synchrotron single-crystal diffraction at low temperatures and ambient pressure. Although mixed satellite reflections are absent, the modulated structure of K V O below 115 K is better described in (3 + 2)- than in (3 + 1)-dimensional space. The geometries of the VO and VO building units are rigid and it is mainly slight rotations of these polyhedra and small variation of the intermediate K-O distances that are modulated. Prolonged exposure to the high-brilliance synchrotron beam suppresses the incommensurate phase. The previously postulated phase transition to the incommensurate phase in Rb V O at 270 K was not observed. One of the reasons could be that the intense radiation also affects the modulation in this material. Strategies to collect and analyse single-crystal diffraction data measured with very intense synchrotron radiation using modern low-noise pixel area detectors are discussed.