Discovery of a new crystalline phase: BiGeO2(OH)2(NO3)

Abstract

A new crystalline phase has been discovered in the Bi₂O₃–GeO₂–HNO₃–H₂O quartet system. The new phase was slowly precipitated at room temperature under atmospheric pressure from a strongly acidic aqueous solution (pH ~0.2) containing dissolved bismuth oxide, germanium oxide, dilute ammonia, and nitric acid. Characterization and crystal structure analyses were carried out by means of powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), thermogravimetry (TG)–mass spectrometric analysis, and solid-state nuclear magnetic resonance (NMR) spectroscopy. The molecular formula was established as BiGeO₂(OH)₂(NO₃). The crystal structure of this new phase was elucidated from PXRD data by a combination of direct and charge-flipping methods. The new phase was found to have the space group Pbca with lattice parameters of a = 1.145510(10) nm, b = 0.495346(5) nm, and c = 1.81676(2) nm. This new phase was observed to possess a layered structure consisting of BiO₆ polyhedra, GeO₅ trigonal bipyramids and nitrate ions.