In-Depth Investigation of the Mechanism of Dehydration-Induced Phase Transformation from NbO(OH) to H-NbO: A Theoretical and Experimental Approach.

H-NbO is a promising energy material, which can be typically obtained from any other polymorph after conducting high temperature calcination (∼1273 K). Recently, a low-temperature dehydration from NbO(OH) was employed to prepare H-NbO at 723 K for 2 h, and yet the transformation mechanism has remained unclear in the literature. Here, the dehydration kinetic and phase transformation mechanism of the NbO(OH) were investigated for the first time by experiments, density functional theory, and molecular dynamics calculations. After dehydration, the orthorhombic NbO(OH) initially transformed into an intermediate Nb-O compound with dislocations, preserving parent structure, and subsequently transformed into monoclinic H-NbO. The activation energy for the transformation from NbO(OH) to H-NbO was as low as 1.35 eV, compared to that of T-NbO to H-NbO (3.60 eV). Furthermore, the defect-rich H-NbO obtained from NbO(OH), does not exhibit pristine bound exciton state due to severe recombination of photogenerated carriers, resulting in poor photocatalytic activity.