Controllable synthesis of BaCuSi2O6 fine particles via a one-pot hydrothermal reaction with enhanced violet colour hue

The present work provides a new approach to address the effect of precursor anions Cl− or NO3− for assisting the one-pot hydrothermal reaction to crystallise BaCuSi2O6 without the addition of pH solution controlling chemicals. The importance of the anionic species role was investigated by comparing two different Cu2+ ion precursors, Cu(NO3)2 and CuCl2; the temperature and reaction time for the hydrothermal treatments as well. The crystallisation of the tetragonal structured BaCuSi2O6 particles occurred at a temperature as low as 180 °C for a reaction interval of 48 h in the hydrothermal media using both Cu2+ precursors. The formation of BaCuSi2O6 particles free of by-products was carried via one-pot processing involving a single-step reaction. The purple Han particles were formed via the dissolution of the coprecipitated precursor gel containing a stoichiometric Ba:Cu:Si molar mixing ratio 1:1:2. Differences on the morphology of the particles were attained to the usage of the Cu2+ precursor. Fine plate-like particles averaging 90 nm size were assembled forming semispherical nest-like agglomerates with an average size of 1.5 µm when Cu(NO3)2 was used, these particles exhibit CIE-L*a*b* colour coordinates of 67.149, 18.164, and −31.562. In contrast, the particles obtained using CuCl2 had other morphology consisted of irregularly shaped aggregates (average size of 1 µm) of fine euhedral BaCuSi2O6; the CIE-L*a*b* colour coordinates for this powder were 68.806, 23.784, and −39.836. All the powders prepared at the optimum conditions exhibited (CIE-L*a*b*) values that correspond to the blue-purple colour spectra space, but the differences on the colour values are affected by the morphological and size variations of the BaCuSi2O6 particles, which were caused by the growth of euhedral BaCuSi2O6 particles averaging 5 µm in size achieved by the dissolution of intermediate 3D hierarchical BaCuSi2O6 particles over 48 h at 200 and 240 °C.