Structural Phase Transitions in the Ferromagnetic Vanadium Oxide NaV6O11 Y. Kamke, F. Izumi, Y. Morii, E. Akiba, S. Funahashi, K. Kato, M. Isobe, E. Takayama-Muromachi, and Y. Uchida [Journal of Solid State Chemistry, 12, pp. 429-437,1994]