Solid-state NMR study of dehydration of layered alpha-niobium phosphate

The dehydration of a representative layered alpha-niobium phosphate (alpha-NbP) was studied by (93)Nb solid state wide-line NMR in combination with several other techniques including X-ray diffraction, thermogravimetric analysis, and (31)P MAS NMR. Four niobium phosphate species associated with dehydration including tri-, di-, and monohydrate phases, as well as a completely dehydrated phase, are identified by (93)Nb NMR. The tri- and dihydrate phases coexist in the as-made alpha-NbP sample. The monohydrate phase formed after heating the sample at 70 degrees C, and an additional anhydrous phase was produced when further dehydrated at 140 degrees C. The dehydration at 250 degrees C resulted in a completely anhydrous phase. The (93)Nb NMR parameters extracted from the wide-line NMR spectra acquired at different magnetic fields are highly sensitive to the dehydration process.