Microhardness measurements (Vicker's hardness number) and x-ray studies have been performed on surface in trigonal plane (111), on single crystal specimens of pure Bi and Bi doped with 4 at. percent of In at room temperature. Vicker's hardness number of Bi-In system is less compared to pure Bi. This result provides a means to make Bi, otherwise a brittle metal, ductile by adding a small quantity of In, which will add to its metallurgical and industrial applications. Further, the Vicker's hardness number is found to be constant along the surface of Bi-In system, implying presence of a uniform phase in it. This suggests that In makes complete solid solution with Bi. The size of atomic radius of In seems to favour substitutional solid solution, where the dopant atoms occupy the sites of the parent atoms and effectively alter the periodicity of Bloch potential and modify the band structure of Bi. Presence of any other phase is not revealed in x-ray diffraction pattern of the Bi-In system and this confirms that the lattice of the doped system is essentially that of bismuth. Cohen's analytical method of least squares refinement for cubic crystals is modified for a hexagonal lattice and employed to calculate the lattice parameters of Bi and Bi-In system. An expansion of the unit cell is reported on account of doping. Laue back-reflection photographs show that 3-fold symmetry of pure bismuth lattice is retained after doping.
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