Abstract

Resonant ultrasound spectroscopy (RUS) has proved to be a powerful method for routine investigation of the elastic and anelastic properties of small polycrystalline or single crystal samples of metals, minerals and functional oxides. The ideal shape is a rectangular parallelepiped with edge dimensions in the range _{1-5 mm. This is placed lightly between two piezoelectric transducers, one of which stimulates natural acoustic resonances in the frequency range} 0.1 – 1.2 MHz and the second of which detects them. Elastic moduli which determine each individual resonance mode scale with f2 and the acoustic loss is determined as the inverse mechanical quality factor, Q-1 = f/f, where f is the resonance frequency and f is its width at half maximum height. Because no glue is required to keep the sample in place, it is easy to design instruments in which RUS spectra can be collected over wide temperature intervals and with the possibility of adding simultaneous electric and/or magnetic fields. The main instrument in Cambridge uses a cryogen-free Oxford Instruments Teslatron to access temperatures down to _{2 K with an external magnetic field of up to 14 Teslas. The high temperature instruments allow routine data collection at temperatures up to} 1200 C.

Applications include the quantitative determination of bulk and shear moduli of ceramics and metal alloys and the use of characteristic Debye-like loss behaviour to detect, for example, hydrogen in steel. The main application in Cambridge has been to investigate the role and dynamics of strain coupling arising at phase transitions, which may be ferroelectric, (anti)ferromagnetic, ferroelastic, multiferroic, relaxor, Jahn-Teller, superconducting, etc. Examples of the methodology and overall approach will be given of the elastic and anelastic behaviour associated with phase transitions in a number of materials, including (Ca,Sr)TiO3 perovskites, the multiferroic perovskite GdMnO3, the helical magnet Cu2SeO3 and the unconventional superconductor, Ba(Fe0.957Co0.043)2As2.

Review article: Journal of Physics: Condensed Matter 26, 263201 (2015)