Rich Behaviors of Vanadium Oxides under High Pressure

Abstract

Vanadium oxides exhibit rich behaviors under high-pressure, for examples, the pressure-temperature (P-T) phase diagram of V 2 O 3 as a prototype of Mott-Hubbard model, a "devil's flower" phase diagram of NaV 2 O 5 derived from the ANNNI model, the pressure-induced superconductivity adjacent to charge order in -A 0.33 V 2 O 5 (A = Li, Na, Ag), a rich P-T phase diagram including the spin-gaped phases with devil's staircase type superlattice modulations in -Sr 0.33 V 2 O 5 , etc. These results reveal that various ground states compete in vanadium oxides and high-pressure give a perturbation to such competition. KEYWORDS:vanadium oxides, metal-insulator transition, charge order, pressure-induced superconductivity, high-pressure IntroductionSince 1949 when the metal-insulator (MI) transition was first observed in V 2 O 3 by Foëx 1) , vanadium oxides have been a central material in the study of strongly correlated electrons. Many compounds exist in binary V-O system, many of which show MI transitions as a function of temperature.2) The MI transitions in mixed valent vanadium oxides such as V 4 O 7 are accompanied by the charge separation and charge order.3) In the extension of our study on vanadium oxides to ternary systems, a novel phase transition like spin-Peierls transition was found in NaV 2 O 5 .

Pressure-induced non-superconducting phase ofβ-Na0.33V2O5and the mechanism of high-pressure phase transitions inβ-Na0.33V2O5andβ-Li0.33V2O5at room temperature

“…The range of phenomena that they exhibit is wide: spin-Peierls transitions, spin gap formation as well as charge and spin ordering. β-A 0.33 V 2 O 5 bronzes (A = Li, Na, Ag) undergo metal-insulator phase transitions with successive charge-spin ordering at atmospheric conditions [6][7][8][9][10][11][12][13][14][15]. They are superconducting below about 9 K at pressures above 7 GPa [6][7][8][9][10][11][12][13][14].…”

“…β-A 0.33 V 2 O 5 bronzes (A = Li, Na, Ag) undergo metal-insulator phase transitions with successive charge-spin ordering at atmospheric conditions [6][7][8][9][10][11][12][13][14][15]. They are superconducting below about 9 K at pressures above 7 GPa [6][7][8][9][10][11][12][13][14]. The exact mechanism of the superconductivity has been debated [7][8][9][10][11][12][13][14] ever since the article by Yamauchi et al has been published [6].…”

“…They are superconducting below about 9 K at pressures above 7 GPa [6][7][8][9][10][11][12][13][14]. The exact mechanism of the superconductivity has been debated [7][8][9][10][11][12][13][14] ever since the article by Yamauchi et al has been published [6]. One of the major problems in understanding the superconductivity is that not all the underlying crystal structures of the (non-)superconducting phases have been determined yet.…”

Effect of Ir[sup 3+] Incorporation on the Luminescent Properties of ZnS:Cl Phosphors

“…12 Recently, it has been reported that Ir incorporation in ZnS:Mn remarkably increases the quantum efficiency of PL. 13 In addition, similar improvements have also been achieved in ZnS:Cu, ZnSe:Mn, and SrS:Ce. 13 Thus, one can expect that this effect also contributes extensively to the improvement of the performance of II-VI-based light-emitting devices such as EL displays.…”

“…13 In addition, similar improvements have also been achieved in ZnS:Cu, ZnSe:Mn, and SrS:Ce. 13 Thus, one can expect that this effect also contributes extensively to the improvement of the performance of II-VI-based light-emitting devices such as EL displays. On the other hand, the mechanism for this improved PL by Ir incorporation has not been investigated to date.…”