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Calcium bismuthate nanoparticles with orthorhombic and rhombohedral crystal lattices were synthesized and characterized by various techniques. The syntheses caused the formation of oxygen and cationic vacancies in bismuth‐deficient samples. Heat treatment of samples with anionic vacancies led to thermal annealing of oxygen vacancies in ambient air; the annealing process was reversible. Oxygen vacancies in Bi‐deficient CaBi6O10 governed the optical absorption beyond the fundamental absorption edge at E(hν) < Ebg ≈ 2.5 eV. Bandgap energies of the bismuthates with orthorhombic and rhombohedral lattices were 2.51 eV prior to annealing and 2.47 eV after annealing at 350 °C. The trend in photoactivity toward the degradation of methylene blue dye under visible light showed that the photoactivity of the orthorhombic samples (1‐3) increased with a decrease in the [Ca]:[Bi] ratio (1.0:6.3 to 1.0:4.3); the sample with lowest ratio (1.0:4.3) displayed highest photoactivity. By contrast, the rhombohedral samples (4‐6) showed increased photoactivity with increase in the number of Bi atoms; sample with highest ratio (1.0:6.3) displayed highest photoactivity.

Experimental evidence is presented that the growth of tungsten whiskers in the process of the NiWO 4 reduction by carbon oxide occurs in accordance with the vapor-liquid-solid mechanism. A liquid phase appears at 940 °C owing to the melting of the NiWO 4 -Na 2 WO 4 eutectic regions which are perhaps results of segregation of sodium impurities included in the reagents used. The presence of the liquid phase ensures for both Ni and W the comparable rates of allocation from the nickel tungstate crystal lattice leading to the formation of the R-W + NiW two-phase regions. The oriented growth of tungsten whiskers during the further reduction of the melt tungstate zones is associated with the W accumulation on the growth surfaces of the W single crystals in the two-phase regions. The result demonstrates that the reactivity of NiWO 4 increases with addition of CuO and Na 2 WO 4 which are capable to form easy-melting phases in the reactive system.

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