Pressure-induced phase transition in NaV₂O₅ at low temperature

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_c0 = 35 K) and C_1/4-phase (2a × 2b × 4c supercell at T < T_c0), 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 < 20K. By measuring temperature dependence of superlattice intensity from the single crystal up to 1.24 GPa for the C_1/4 - and C₀-phases, we obtain the temperature-pressure phase diagram. The P-to-C_1/4 phase transition is significantly suppressed as (dT_c0/dP) ∼ -11(1) (K/GPa) at 0.1 MPa (1 atm.) while the C_1/4-to-C₀ phase transition takes place at P_c = 0.92 GPa nearly independent of temperature below 20K.