An anomalous downsizing of glycothermally-synthesized YBO₃ crystals by Ce³⁺ doping

We have systematically investigated the effects of rare-earth doping on the size and morphology of YBO₃ crystals prepared by a glycothermal method. Spheroidal particles of YBO₃ crystals doped with 1 at% of various rare-earth ions are prepared from trimethyl borate and acetates of rare-earths via a glycothermal reaction at 300 °C for 2 h in 1,4-butanediol. Ce³⁺-doped YBO₃ shows remarkably small particles of ~180 nm in diameter, while undoped and other rare-earth-doped YBO₃ consist of spheroidal particles of ~1 μm in diameter. This downsizing phenomenon for Ce³⁺-doped YBO₃ is attributed to neither local lattice distortions nor surface adsorbed species. The downsizing is also observed when other cerium compounds, i.e., cerium nitrate, chloride, acetylacetonato, and oxide, are used as a cerium source. Investigation on the crystal growth process of Ce³⁺-doped YBO₃ reveals that cerium ions promote the nucleation of YBO₃ crystals at the early stage of the reaction, resulting in small particles.