In-situ X-ray powder diffraction studies of hydrothermal and thermal decomposition reactions of basic bismuth(III) nitrates in the temperature range 20-650 °C

The syntheses of basic bismuth(in) nitrates under hydrothermal conditions and their dry decomposition to alpha-Bi2O3 in solid-state reactions was investigated by in-situ synchrotron X-ray radiation powder diffraction. Three basic bismuth(III) nitrates with known structures are: [Bi6O4(OH)(4)](NO3)(6).4H(2)O, C, [Bi6O4(OH)(4)](NO3)(6).H2O, D, and [Bi6O5(OH)(3)](NO3)(5).3H(2)O, A. They contain the complex ions [Bi6O4(OH)(4)](6+) and {[Bi6O5(OH)(3)](5+)}(2), respectively. A fourth basic bismuth(III) nitrated X, apparently has the composition [Bi6O4.5(OH)(3.5)](NO3)(5.5).H2O according to chemical analysis. The transformation of C via D to X, or of C directly to X was established in the in-situ hydrothermal synthesis. Similarities in the decomposition paths of C, D and X in the solid-state in-situ investigations support the above composition indicated for X. The compound A has a decomposition path different from those of C D and X. This is consistent with the complex ion {[Bi6O5(OH)(3)](5+)}(2) in A, being different from the complex ion [Bi6O4(OH)(4)](6+) in the other two basic bismuth(III) nitrates. All four compounds have alpha-Bi2O3 as the final decomposition product.