Effect of the Anisotropy Mechanical Properties on LN Crystals Fixed-Abrasive Lapping

The anisotropy of lithium niobate (LN) single crystals in mechanical properties affects its material removal uniformity during lapping. The nano-indentation hardness (H_I) and elastic modulus(E) of Z-cut wafer and X-cut wafer were measured by a nano-indentation tester. The nano-scratching tests were adopted to evaluate its critical cutting depth (d) of brittle ductile transition along crucial orientations of Z-cut and X-cut, respectively. A series of fixed-abrasive lapping tests were carried out to explore the effect of anisotropy on the lapping process. The results indicated that the H_I of Z-cut was slightly higher than that of X-cut, while the E of Z-cut was about 1.1 times of the latter. The d value of each orientation varies greatly. The lapping tests showed that the material removal rate (MRR) of Z-cut was lower than that of X-cut, for its high H_I and E. Meanwhile, the surface quality of Z-cut was better than that of X-cut, for the larger d of Z-cut. The research of mechanical properties of LN has guiding significance for its lapping process.