Pressure-Induced Phase Transition in NaV₂O₅ at Low Temperature

抄録

Pressure effect on phase transition in NaV₂O₅ has been studied at low temperature by x-ray scattering. In addition to two well-known phases at ambient pressure such as P-phase (a × b × c orthorhombic unit cell at T>T_{c_ 0} = 35 K) and C_¼-phase (2a × 2b × 4c supercell at Tc_ 0 ), we discovered a new high-pressure phase C₀-phase, which has a 2a × 2b × 1c supercell and is considered to be a new ground state above 0.92 GPa at T<20 K. By measuring temperature dependence of superlattice intensity from the single crystal up to 1.24 GPa for the C_¼- and C₀-phases, we obtain the temperature-pressure phase diagram. The P-to-C_¼ phase transition is significantly suppressed as (dT_{c_ 0} /dP)-- -11(1) (K/GPa) at 0.1 MPa (1 atm.) while the C_¼-to-C₀ phase transition takes place at P_c= 0.92 GPa nearly independent of temperature below 20 K.