Pressure dependence of phase transitions in the quasi-one-dimensional metal-insulator transition system β-Na_1/3V₂O₅

The pressure dependence of phase transitions in the quasi-one-dimensional vanadium oxide β-Na_1/3V₂O₅ has been studied by magnetic susceptibility and electrical resistivity measurements. The pressure dependence of the various transition temperatures is quite different. The transition at T=240 K, previously reported and attributed to ordering on Na sites, and a second transition at T≈222 K, reported here and attributed to a further increase of order on Na sites, are almost independent of pressure. On the other hand, the metal-insulator (MI) transition at T_MI=130 K shifts to lower temperatures, while the magnetic transition at T_N=24 K shifts to higher temperatures with increasing pressure. We discuss the different pressure dependencies of T_MI and T_N in terms of increasing interchain coupling and the MI transition to be of Peierls type.