Effect of Na-deficiency on the spin-Peierls transition in α′-NaV2O5

We have investigated the phase diagram of NachiV2O5 in the composition range 0.7 less than or equal to x less than or equal to 1.5 and the effect of Na-deficiency on the spin-Peierls transition in the quasi-one-dimensional (1D) magnet alpha'-NaV2O5. The alpha'-NaV2O5 phase exists in the composition range 0.80 less than or equal to chi less than or equal to 1.00. The spin-Peierls transition is suppressed by Na-deficiency and disappears around chi = 0.97. The Curie-like increase of magnetic susceptibility was observed in alpha'-NaV2O5 at low temperature. Any evidence for a magnetic order in alpha'-NaV2O5 has never been observed in contrast to the Zn-doped CuGeO3 or SrCu2O3. The electric resistivity decreases with Na-deficiency, although alpha'-NachiV2O5 remains semiconductive in 0.80 less than or equal to chi less than or equal to 1.00. The temperature dependence of conductivity for the Na-deficient samples seems to be consistent with a variable range hopping in the 1D system. This suggests that the carriers are doped into the 1D chain by Na-deficiency but do not induce clean metallic behavior. We also report a low dimensional behavior in the magnetic susceptibility and a possible spin singlet state as the ground state in Na1.3V2O5 (the eta-phase). (C) 1997 Elsevier Science S.A.