High-pressure x-ray diffraction experiments on icosahedral Ti-Zr-Ni-unusual effects due to a low shear modulus and a high Poisson's ratio

In situ high-pressure x-ray diffraction experiments have been performed on quasicrystalline Ti-Zr-Ni in energy-dispersive mode using synchrotron radia tion. Pressures up to 30 GPa were generated using a diamond anvil cell. The bulk modulus of Ti-Zr-Ni was determined to be B-0 = 166 GPa +/- 13 GPa. So me of the experiments were performed under slightly nonhydrostatic conditio ns. In these runs, deviations from a standard equation of state could be ob served and these are due to additional strains. According to the model of S ingh and Kennedy for elastically isotropic solids, these strains are propor tional to the non-hydrostatic stress component and indirectly proportional to the shear modulus of the sample. From our measurements, the shear modulu s of icosahedral Ti-Zr-Ni was estimated to be mu approximate to 7 GPa with a relative error of about 50%. This value is low compared to the shear modu li of icosahedral Al-Cu-Fe, Al-Pd-Mn (for both, mu approximate to 65 GPa) a nd Al-Li-Cu (mu = 38 GPa). The Poisson's ratio of Ti-Zr-Ni was determined t o be nu = 0.48 +/- 0.015. This value is close to the maximum value which is allowed by the laws of thermodynamics, namely nu = 0.5. The Poisson's rati os of common metals (nu approximate to 1/3) and other icosahedral alloys li ke Al-Cu-Fe (nu = 0.19), Al-Pd-Mn (nu = 0.28) and Al-Li-Cu (nu = 0.25) are much lower.