Systematics in the metal-insulator transition temperatures in vanadium oxides

Nine of the known vanadium oxides, VO2-1/n (n - a positive or negative integer) with n=2-6,8,9, infinity and -6, undergo metal-insulator transitions accompanied by structural transitions, at various temperatures T-MIT (V7O13 is metallic above T=0). Among the persistent efforts to determine the driving force (s) of these transitions, electron-electron (Mott-like) and electron-phonon (Peierls-like) interactions, there were several attempts to find systematics in T-MIT as function of n. Here we present an unexpectedly simple and illuminating systematics that holds for positive n: if T-MIT is the absolute value of the difference between T-M(n) and T-P(n), which represent the contributions of electron-electron and electronphonon interactions, respectively, all data points of T-M-T-P versus 1/n lie on, or close to, two simple straight lines; one is T-M-T-P =T-infinity(7/n 1) for V3O5, V4O7, V5O9, V7O13, V8O15, V9O17 and VO2 and the other is T-M-T-P=T-infinity(3/n-1) for V2O3, V6O11 and VO2. (C) 2015 Elsevier Ltd. All rights reserved.