Abstract
The anisotropy of lithium niobate (LN) single crystals in mechanical properties affects its material removal uniformity during lapping. The nano-indentation hardness (HI) 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 (dc) 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 HI 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 dc 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 HI and E. Meanwhile, the surface quality of Z-cut was better than that of X-cut, for the larger dc of Z-cut. The research of mechanical properties of LN has guiding significance for its lapping process.
Highlights
Lithium niobate (LN) crystal is one of multi-functional materials which owns piezoelectric, ferroelectric, pyroelectric, nonlinear, lightning, and photorefractive properties, together with a good thermal stability and chemical stability
Ultra-precision machined surfaces is the prerequisite for the application of LN crystals in each field
LN crystal is a typical strong anisotropy soft-brittle crystal, with a thermal expansion coefficient of the a axis being more than eight times that of c axis (16.7 × 10−6 of a axis and 2.0 × 10−6 of c axis, respectively), and with different optical performance on each plane [3,4]
Summary
Lithium niobate (LN) crystal is one of multi-functional materials which owns piezoelectric, ferroelectric, pyroelectric, nonlinear, lightning, and photorefractive properties, together with a good thermal stability and chemical stability. It has been applied on the surface acoustic wave filter, optical waveguide substrate, and infrared detectors, etc. The difference in mechanical properties on different planes and orientations reduces the controllability of ultra-precision processes (here mainly refers to lapping and polishing process). In order to realize the ultra-precision machining of LN crystal, the research of the influence of anisotropy mechanical properties on the machining process is indispensable
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