School of Mechanical Engineering Yotam Hirsh

School of Mechanical Engineering Seminar
Wednesday, Oct 25, 2017 at 14:00
Wolfson Building of Mechanical Engineering, Room 130

 Evaluating the cleavage energies of Lithium Niobate (LiNbO₃) crystal

Yotam Hirsh

MSc. Student of Prof. Dov Sherman

The cleavage energy of brittle single crystal is scarce due to the difficulties to perform controlled and accurate fracture experiments in these materials. The first estimation would be the lower bound of the cleavage energy, twice the free and relaxed surface energy, or 2g_s, known as Griffith barrier. The most common crystals structures are cubic and hexagonal structures, most of the efforts fracture wise, have been directed toward cubic single crystal silicon. This research explores the second most common structure, the hexagonal crystal structure, where Lithium Niobate (LiNbO₃) is the targeted material. The structure of LiNbO₃ crystal is challenging due to his special thermal expansion behavior and anisotropic mechanical properties in the orthogonal space. This crystal has been widely studied for its physical and optical properties. However, very limited information exists for its fracture properties, cleavage planes, the free surface energy, etc. Our results would be the first time cleavge energies would be given for this hexagonal LiNbO₃ crystal.

We will present our high resolution fracture experiments, performed using our Coefficient of Thermal Expansion Mismatch (CTEM) method, employing heating as the driving force for fracture. Finite element analysis (FEA) was used as a calculation tool to evaluate the cleavage energy of the material in difference cleavage systems. Preliminary results will be presented and discussed.