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 BaCuSi₂O_6; 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.