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

Abstract

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.