Observation of pressure-induced superconductivity in β-LixV2O5

Highly hydrostatic high pressure study on β-LixV2O5 (x ∼ 0.36 and 0.33) up to about 11 GPa has been carried out, conquering many experimental difficulties, where the resistivity has been successfully measured beyond 10 GPa. The charge order suppresses with increasing pressure and the superconducting transition appears around 8.5 K and 9.8 GPa. The present study reveals that all A+-compounds (A+ = Li, Na, Ag) among β-vanadium bronzes exhibit pressure induced superconductivity in contrast to the absence of superconductivity in all A2+-compounds (A2+ = Ca, Sr, Pb). The obtained pressure–temperature (P–T) electronic phase diagram suggests two kinds of superconducting phases; the low Tsc (4.5 K) and the high Tsc (8.5 K) phases in β-Li0.36V2O5. Such coexistence of two superconducting phases is discussed in terms of the phase separation into β and β′ structures with common V2O5-framework, which is inherent in β-LixV2O5.