Elastic properties of β-eucryptite in the glassy and microcracked crystalline states

Amorphous and crystalline β-eucryptite (LiAlSiO4) specimens were prepared with controlled grain sizes and varying levels of microcracking, and their elastic moduli were determined using resonant ultrasound spectroscopy. It was found that the relationship between Young’s modulus, Poisson’s ratio and degree of microcracking in these materials can be described well with fracture-mechanics-based models. It was also found that if glassy β-eucryptite is considered to be a microcracked medium in which broken Si–O bonds, with respect to the crystalline material, constitute microcracks, then its elastic properties can be described equally well by these models. Such considerations are explained by noting the differences in atomic bond density among the different states of the material and by accounting for differences in strain energy release rate measurements on glass and ceramic specimens.