 Sintering powders of samarium oxide and boron , in vacuum , yields a powder containing several samarium boride phases , and their volume ratio can be controlled through the mixing proportion . The powder can be converted into larger crystals of a certain samarium boride using arc melting or zone melting techniques , relying on the different melting / crystallization temperature of SmB6 ( 2580 ° C ) , SmB4 ( about 2300 ° C ) and SmB66 ( 2150 ° C ) . All these materials are hard , brittle , dark @-@ gray solids with the hardness increasing with the boron content . Samarium diboride is too volatile to be produced with these methods and requires high pressure ( about 65 kbar ) and low temperatures between 1140 and 1240 ° C to stabilize its growth . Increasing the temperature results in the preferential formations of SmB6 . 
