Pressure-Induced Phase Transition in NaV_2O_5 at Low Temperature : Condensed Matter: Structure, etc.

概要

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Pressure effect on phase transition in NaV_2O_5 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> = 35K) and C_<1/4>-phase (2a × 2b × 4c supercell at T < T_<c_0>), we discovered a new high-pressure phase C_0-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_<1/4>- and C_0-phases, we obtain the temperature-pressure phase diagram. The P-to-C_<1/4> phase transition is significantly suppressed as (dT_<c_0>/dP) 〜 -11(1) (K/GPa) at 0.1 MPa (1 atm.) while the C_<1/4>-to-C_0 phase transition takes place at P_c = 0.92GPa nearly independent of temperature below 20 K.
2000-03-15