Resonant ultrasound spectroscopy measures the mechanical resonances of a crystal weakly coupled to drive and receive transducers. These mechanical resonant modes are determined by the sample shape, density, crystal symmetry, and elastic moduli.

Resonant ultrasound spectroscopy (RUS) measures the

frequencies, f, and widths, Γ, of the vibrational normal

modes of a crystal acting as a free mechanical resonator.

The frequencies of the normal modes are determined by the

density and geometry of the crystal as well as by its elastic

properties. The elastic component of the temperature

evolution of these frequencies, Δf(T), depends on a linear

combination of all elastic moduli and reflects changes in the

thermodynamic state of the system such as those

associated with a phase transition.