Microhardness and X-ray studies of single crystals of Bi doped with group IV elements, Pb and Ge

59-64Microhardness tests and X-ray studies performed on single crystals of pure Bi, Bi-Pb (3at.%) and Bi-Ge (2at.%) in trigonal direction [111] at room temperature reveal quite contrasting features for Pb and Ge as dopants, despite the fact that both of these belong to group IV of periodic table of elements. It is reported that Pb has a hardening effect on the bismuth lattice, whereas Ge has softening effect on bismuth lattice. This result may find many metallu rgical and industrial applications. The Vicker's hardness number increased to a value of 13.9 for Bi-Pb system, whereas it decreased to a value of 11.8 for Bi-Ge system, compared to a value of 12.4 for pure Bi. Microhardness tests and X-ray studies indicate Pb and Ge make predominantly a solid solution with bismuth by substituting for Bi atoms at various lattice sites with small discontinuous traces of second phase scattered over a uniform main phase. In Bi-Pb system this second phase is identified to be the ɛ phase comprising of Bi dissolved in Pb and in Bi-Ge system the second phase is identified to be the segregated Ge, rejected by the Bi lattice on account of limited solubility of Ge in Bi. XRD patterns reveal that the lattices of the doped systems are largely those of bismuth and volume fraction of second phase is negligibly small in both the systems. Cohen's method of least squares refinement for cubic system is modified for Bi lattice, indexed on hexagonal axis and a system of normal equations is set up for pure Bi and both the doped systems. These equations are subjected to least squares treatment to obtain lattice parameters, a and c, of pure Bi, Bi-Pb and Bi-Ge systems. It is reported while the unit cell of pure Bi expands, when Pb is added to it, it contracts when Ge is added to it. Laue back-reflection photographs taken along trigonal [111] direction show that 3-fold symmetry of pure bismuth lattice is retained after doping also