 Samarium carbides are prepared by melting a graphite @-@ metal mixture in an inert atmosphere . After the synthesis , they are unstable in air and are studied also under inert atmosphere . Samarium monophosphide SmP is a semiconductor with the bandgap of 1 @.@ 10 eV , the same as in silicon , and high electrical conductivity of n @-@ type . It can be prepared by annealing at 1100 ° C an evacuated quartz ampoule containing mixed powders of phosphorus and samarium . Phosphorus is highly volatile at high temperatures and may explode , thus the heating rate has to be kept well below 1 ° C / min . Similar procedure is adopted for the monarsenide SmAs , but the synthesis temperature is higher at 1800 ° C. 
