On the low-temperature structure and magnetic behaviour of   - Na 1.286 V 2 O 5

In this work, we report on low-temperature x-ray diffraction, electron-spin-resonance and magnetic-susceptibility measurements performed on η-Na1.286V2O5. We show that the low-temperature structure of this compound differs from that at room temperature mainly by the doubling of the unit cell in the b direction. The magnetic measurements give evidence for the opening of a spin gap which we discuss in conjunction with the low-temperature structure of this compound.