Twinning and defects in N-Nb2O5

N-Nb2O5 [C2/m (No. 12), a = 28.51, b = 3.830 and c = 17.48 Angstrom, and be ta = 124.8 degrees] has been investigated by means of selected-area electro n 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 sometime s be best explained as stacking faults. A second type of coherent twinning at an angle of 90 degrees 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.