Obtaining of crystals of polyelemental solid solutions of rare earth hexaborides

Single crystals of polyelemental rare earth hexaborides with the preset formula La$_{0.5}$(Ce$_{0.1}$Pr$_{0.1}$Nd$_{0.1}$ Sm$_{0.1}$Eu$_{0.1}$)B$_{6}$ were obtained for the first time. Synthesis and crystallization were performed by the solution–melt method in an immiscible Al/Pb system. Step-by-step chemical analysis was made with the aid of a CAMEBAX microprobe. The inclusion of all rare earth metals (REMs) in the hexaboride lattice was proven, and differences in the composition of obtained crystals caused by nonstationarity of the bulk crystallization process were found. The lattice periods of the polyelemental REM hexaborides were found to be smaller than that of hexaboride of lanthanum, the main element of the metal sublattice. The measured microhardness of the new material lies within the range of the microhardness values of hexaborides of all its constituent REMs. Speculations are provided on the peculiarities of the growth mechanism, crystallization, and composition of the obtained crystals.