Keywords: Co-precipitation Surfactant free Molybdates Morphology Rietveld refinement Band gap tuning

In this work, a series of Sr1-xBaxMoO4, Sr1-xCaxMoO4, and Sr1-2xCaxBaxMoO4 nanocrystal solid-solutions with well-defined morphologies have been prepared by a surfactant-free coprecipitation method at room temperature. X-ray diffraction, Rietveld refinement data, Fourier transform Raman, and Fourier transform infrared spectroscopies confirmed the formation of continuous-solid solutions over the entire composition range for Sr1-xCaxMoO4 and Sr1-xBaxMoO4. The substitution of Ca and Ba for Sr in Sr1-2xCaxBaxMoO4 leads to phase-pure powders where x <= 0.1. X-ray fluorescence spectroscopy confirms that the actual composition is close to the nominal stoichiometry of the samples. The molybdate powders are composed of micronic particles having diverse morphologies, including shuttle, microsphere, flower, dumbbell, and spindle. These superstructures are composed of primary particles having an average particle size of less than 60 nm. The optical band gap of Sr1-xBaxMoO4 and Sr1-xCaxMoO4 varies from 4.17 to 4.34 and 4.17 to 3.87 eV, respectively, with the chemical composition (x). The bandgap of Sr1-2xCaxBaxMoO4 is not significantly affected by variation of the nominal composition(x). The relatively small bandgap bowing parameter indicates good miscibility of the alloying constituents.

Automated summary

In this study, a series of well-defined nanocrystal solid-solutions with different morphologies were prepared by a surfactant-free coprecipitation method. The formation of these solid-solutions, as well as the composition and structure of the powders, were confirmed by various characterization techniques. The nanocrystal solid-solutions exhibited a relatively small bandgap bowing parameter, indicating good miscibility between the alloying constituents.