Theoretical Analysis and Experimental Verification of Triangular Fracture Defects of MgO Single Crystal Substrate in Lapping or Polishing Process

MgO single crystal is mainly used as substrate for high temperature superconductor film. Surface quality of MgO substrate has significant effect on the function of high temperature superconductor film. MgO single crystal is a typical hard and brittle material, and is easily cleaved along the {100} face, so some defects are always generated on the substrate surface while lapping and polishing, which badly affects the surface quality of the substrate. In this paper, a kind of typical defect, the triangular fracture defect which is on the substrate surface after lapping and polishing, is analyzed in detail. According to the structure characteristics of the MgO single crystal, and based on the dislocation reaction theory, a formation mechanism of the triangular fracture defect in lapping and polishing processes is explored. Through the single grain scratch test in different directions on the polished surface of MgO{100} single crystal substrates, the formation mechanism of triangular fracture defect in lapping and polishing processes is verified. And during the scratch test, the plastic flow of the MgO single crystal material beside the scratch was observed.