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 x b x c orthorhombic unit cell at T > Tc0 = 35 K) and C1/4-phase (2a x 2b x 4c supercell at T < Tc0), we discovered a new high-pressure phase C0-phase, which has a 2a x 2b x 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 C1/4-and C0-phases, we obtain the temperature-pressure phase diagram. The P-to-C1/4 phase transition is significantly suppressed as (dTc0/dP) ∼-11(1) (K/GPa) at 0.1 MPa (1 atm.) while the C1/4-to-C0 phase transition takes place at PC = 0.92 GPa nearly independent of temperature below 20 K. (author)