A new anhydrous bismuth potassium nitrate, K_3Bi_2(NO_3)_9: Synthesis, structure characterization and thermal decomposition

摘要

A new K_3Bi_2(NO_3)_9 phase was discovered at a synthesis of Bi-containing photocatalysts. K_3Bi_2(NO_3)_9 has cubic structure with unit cell parameter a = 13.5354(20)A, and belongs to P4_332 (No. 212) space group. New phase is isostructural with the K_3Ln_2(NO_3)_9 (Ln = La, Ce, Pr, Nd, and Sm) phases. The crystal structure was refined from powder X-ray diffraction (XRD) data. The R_(wp) factor at Rietveld refinement was equal to 8.62%. The morphology of K_3Bi_2(NO_3)_9 was characterized using scanning electron microscopy. The value of ionic radius of Bi~(3+) in 12-fold coordination calculated from the unit cell parameter was found to be 1.314(5) A. K_3Bi_2(NO_3)_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, K_3Bi_2(NO_3)_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.