Abstract

The microscopic origin of the various phase transitions which have been observed in g -Na 0.33 V 2 O 5 and its analogues can be explored experimentally by investigating the oxygen isotope effect on the phase transition temperatures. An absent oxygen isotope effect on the sodium-ordering transition would point to an antiferroelectrically driven instability, while a large isotope effect on the charge ordering and spin ordering transition temperatures would suggest the formation of a charge-density wave instability and phonon mediated long-range magnetic ordering. All instabilities can be attributed to strong electron-phonon interaction effects, which dominate the ground-state properties