Elastic constants of single crystals of the three phases of In---Pb alloys |
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Authors: | M.R. Madhava G.A. Saunders |
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Affiliation: | University of Bath, School of Physics, Claverton Down, Bath BA2 7AY, England |
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Abstract: | In a study of the elastic behaviour of the InPb alloys, the elastic stiffness tensor components of crystals of each of the three phases (fct, ; fct, ; fcc) have been obtained as a function of temperature from pulse superposition measurements of ultrasonic wave velocities. Comparison of the elastic stiffness constants obtained for a fct () 5 atm.% Pb alloy with those of In itself and those of InTl and InCd alloys, establishes for this phase that alloying with Pb, as with TI and Cd, enhances the softening of the acoustic [110] phonon mode, polarization [10] near the Brillouin zone centre. The elastic properties of a 17 atm.% Pb crystal, which is in the fct () phase, are quite different from those shown by In alloys in the fct ( phase; in particular the response to a shear stress is remarkably isotropie: there is no phonon mode softening in this alloy. Neither is there softening of this mode (which corresponds at the zone centre to the shear stiffness (C11;C12)) in crystals of the fee phase — in complete contrast to the dominating influence of the softening of (C11;C12) in the InTl and InCd fee alloys. In fact for a fcc In-75 atm.% Pb alloy the anistropy ratio for shear is close to unity. The transitions between the three phases of the InPb alloys are markedly first order and acoustic mode softening has a much smaller influence on the elastic behaviour of the fct () and fcc InPb alloys than it has on the fct () InPb, InCd and InTl alloys. |
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