Twinning and defects in N-Nb2O5

N‐Nb2O5 [C2/m (No. 12), a = 28.51, b = 3.830 and c = 17.48 Å, and β = 124.8°] has been investigated by means of selected‐area electron diffraction (SAED) and high‐resolution transmission electron microscopy (HRTEM). N‐Nb2O5 is domain twinned, with the twin plane perpendicular to the c* axis. The domains are rather small and the domain twinning can sometimes be best explained as stacking faults. A second type of coherent twinning at an angle of 90° to the other two domain directions was also found. These domains are linked together by areas containing blocks of different sizes, similar to the disordered block arrangement observed in M‐Nb2O5.