MECHANICAL PROPERTIES OF THE MONOCRYSTALS OF LANTHANUM HEXABORIDE

We find the modulus of elasticity, microhardness, crack resistance, and specific resistance of the monocrystals of lanthanum hexaboride with perfect structure that can be used as reference data. The energy of covalent bond between the B–B atoms and the total energy of binding of LaB 6 and diborides of transition metals are computed. These data are used to explain high mechanical characteristics of lanthanum hexaboride. In the family of 15 hexaborides of lanthanides, the structure and properties of lanthanum hexaboride are studied especially comprehensively [1]. However, since the data of different authors on its composition in the region of homogeneity are contradictory, it is necessary to perform additional investigations. It should be taken into account that lanthanum hexaboride is a phase of variable composition with inaccurately determined region of homogeneity (from LaB 6 to LaB 6.13 ). Therefore, according to the phase diagram, its melting point may vary within the range 2052 – 2715°C, which definitely affects its properties. The work function of electrons for LaB6 monocrystals and their mechanical and electrophysical properties obtained in the installations for noncrucible zone melting strongly depend on the structure and defects of the lattice cells [2]. Since LaB 6 crystallizes under nonequilibrium conditions [3], the analysis of its structural perfection is an urgent problem in getting single crystals with the optimal properties.