A new anhydrous bismuth potassium nitrate, K3Bi2(NO3)9: Synthesis, structure characterization and thermal decomposition

A new K3Bi2(NO3)9 phase was discovered at a synthesis of Bi-containing photocatalysts. K3Bi2(NO3)9 has cubic structure with unit cell parameter a = 13.5354(20) Å, and belongs to P4332 (No. 212) space group. New phase is isostructural with the K3Ln2(NO3)9 (Ln = La, Ce, Pr, Nd, and Sm) phases. The crystal structure was refined from powder X-ray diffraction (XRD) data. The Rwp factor at Rietveld refinement was equal to 8.62%. The morphology of K3Bi2(NO3)9 was characterized using scanning electron microscopy. The value of ionic radius of Bi3+ in 12-fold coordination calculated from the unit cell parameter was found to be 1.314(5) Å. K3Bi2(NO3)9 phase and products of its thermal decomposition were studied using XRD, Fourier transform infrared spectroscopy (FTIR) methods and thermal gravimetric analysis (TGA). At 350 °C, K3Bi2(NO3)9 phase was transformed to new unknown intermediate bismuth potassium nitrate that most likely belongs to Sillen type of structure. Geometrical solution for unit cell of this phase was proposed.

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► New K3Bi2(NO3)9 phase isostructural with the K3Ln2(NO3)9 (Ln = La, Ce, Pr, Nd, and Sm) phases was discovered at synthesis of Bi-containing compounds.
► Structure was refined using Rietveld procedure.
► Bi3+ ionic radius in 12-fold configuration in K3Ln2(NO3)9 structures was determined.
► Products of thermal decomposition of new phase were studied using XRD, FTIR and TG methods.