Unique Structural Features of NbS3 Ribbon Whiskers

Abstract

The X-ray diffraction analysis of NbS3 ribbon whiskers has revealed three structural features: (i) a fine-crystalline structure throughout the entire volume with the preferred orientation along the [001] direction perpendicular to the long b axis of the whisker, (ii) the combination of crystalline macroblocks with a length up to 0.5 mm with small crystallites of various orientations, and (iii) the combination of crystalline macroblocks with the left-hand twisting of planes around the b axis with a pitch angle of 1.25° per every 0.2 mm and with the return to the initial orientation in the next block. Structural features (ii) and (iii) of NbS3 whiskers have not yet been observed, and inorganic crystals with such properties are absent to the best of our knowledge. All crystallites have a unit cell with almost right angles and approximately the same lattice constant c (18.130 Å), whereas the lattice constants a and b are noticeably different in a single sample. All crystallites can be referred to phase IV rather than to phase I, as expected. The right angle between the a and c axes can be explained by the twinning of phase I along the c axis. Differences in the lattice constants in macroblocks indicate large stresses in structures. Such stresses near twins (and/or stacking faults) can significantly affect the free electron density and play a key role in the formation of charge density waves in various phases of NbS3.