The structure of NBZ was studied by neutron diffraction. NBZ is monoclinic, (SG #11 P21/m) am = 5.696(8) Å, bm = 8.166(9) Å, cm = 5.790(4) Å and βm = 89.97(4)°. Being centrosymmetric, NBZ is neither piezoelectric nor ferroelectric. No phase transition was evidenced between 100 K and 923 K. NBZ presents a relaxor behavior below room temperature attributed to the mixed occupancy of the A-site by both Na + and Bi 3+ ions. The relative permittivity of NBZ appears noticeably stable (for 1 kHz-2.9% at-55 °C / 218K and +5.3% at 85 °C / 358 K compared to the 25 °C / 298 K value). NBZ appears thus as promising for the elaboration of capacitors requiring high thermal stability