Thermal shock cracking of lithium niobate single crystal

Abstract

The quantitative estimation of failure stress of a lithium niobate (LN) single crystal due to thermal shock was investigated. Cylindrical test specimens were used in the thermal shock tests. The thermal stress of an LN test specimen under conditions of thermal shock cracking was calculated from a computer program which takes account of the crystal anisotropy, using the surface temperature measured in the thermal shock test. Four-point bending tests were also carried out to examine the relationship between the thermal shock cracking and the failure of a small test specimen due to mechanical load. LN single crystals fractured at the cleavage planes {0 1 1 2} in the thermal shock test and the four-point bending test. Although the failure stress data obtained from both tests obey the Weibull distribution, the Weibull distribution depends not only on specimen size but also on loading type. According to the Weibull distribution of thermal shock test data, if the normal stress σ_n acting on the cleavage planes {0 1 1 2} is lower than 10 MPa, the probability of thermal shock cracking becomes very small — less than 2%.