A versatile route for the convenient synthesis of rare-earth and alkaline-earth hexaborides at mild temperatures

In this study, a versatile route is reported for the convenient synthesis of rare-earth hexaborides (RB6, R = La, Ce, Pr, Nd, Sm, Eu) and alkaline-earth hexaborides (AB6, A = Ca, Sr, Ba). The single crystalline cube-like RB6 (R = La, Ce, Pr, Sm, Eu) with mean sizes ranging from 450 to 700 nm were prepared through the co-reduction of rare-earth oxides and boric acid by Mg powder with the assistance of I2 at 170–250 °C. Similarly, NdB6 as well as AB6 (A = Ca, Sr, Ba) can be produced at 350 °C. It is found that CaB6 nanorods with a proportion above 20% and lengths up to several micrometres were produced using CaO as calcium source. When CaCO3 was used instead of CaO, single crystalline hollow CaB6 cages were obtained at 400 °C. The cube-like LaB6 was taken as an example for the synthesis of a series of hexaborides by adjusting the experimental parameters.