Resonant Ultrasound Spectroscopy of Solids: Hydrogen-Metal and Other Systems

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0070808LeisureIn this project Resonant Ultrasonic Spectroscopy (RUS) will be used to study the properties of materials usually shaped into spheres, cylinders or parallelopipeds. RUS is based on the measurement of the vibrational eigenmodes of such samples. The RUS spectrum yields the full set of elastic constants as well as the ultrasonic attenuation of the material composing the sample. Very small size samples can be studied with this tecnique. A major thrust of this work will be the study of hydrogen-metal systems including quasicrystalline, Laves-phase and rare-earth materials. Experiments on the quasicrystalline systems Ti-Zr-Ni, Al-Pd-Mn and Zn-Hg-Ho will attempt to obtain information about H diffusion in a non-periodic potential and use hydrogen as a probe of the local symmetry. RUS will be expected to contribute to the clarification of the hydrogen hopping phenomenon by providing data complementary to those obtained by conventional NMR and neutron scattering experiments. Experiments in the millikelvin range on the hcp rare-earth type metals and Laves-phase materials will search for the resonant and relaxation effects of hydrogen transitions on the low-temperature acoustic properties. The results will be correlated with modern theories of dissipative tunneling in a double-well potential. RUS will also be applied to the study of phase transitions. Elastic constant data for Ce-based magnetic compounds near their magnetic transition temperatures (2-30K) should provide valuable thermodynamic information related to the volume dependence of the competing Kondo and RKKY interactions. The moduli of Mg2NiH4 will be studied to gain insight into the nature of the change to an apparent conducting state. This research is facilitated by the involvement of graduate and undergraduate students. Their training in a contemporary area of condensed matter physics and materials science will prepare them to enter the workforce during the next few decades of this Century. %%%A technique called Resonant Ultrasound Spectroscopy (RUS) will be employed to study the elastic vibrations of solids. These measurements provide data about the rigidity/stiffness of the material. Only small samples are required, their small size implying that the vibrational frequencies are in the ultrasound, i.e., inaudible range of frequencies. The method will be applied to the study of hydrogen in metals. Hydrogen in metals is of both fundamental and practical interest. Practical uses of hydrogen-in-metal systems include their employment in batteries and their use for hydrogen storage. High mobility of the hydrogen within the metal is usually required for successful applications. The addition of hydrogen to metals affects the elasticity of these materials. These changes in the elastic properties of the hydrogen containing metals are studied by the RUS technique. Graduate and undergraduate students will participate in this research. They will thereby acquire knowledge and skills in experimental and theoretical condensed matter physics and materials science that will prepare them to be productive members of the workforce during the next few decades of this Century. ***