Room‐temperature plastic deformation of single crystals of high‐purity β‐silicon nitride investigated by micropillar compression

The room‐temperature plastic deformation behavior of single crystals of high‐purity β‐silicon nitride has been investigated by micropillar compression tests as a function of loading‐axis orientation and specimen size. Prism < c > slip ({010}[0001] slip) is identified to be the only operative slip system under uniaxial compression at room temperature. The critical resolved shear stress (CRSS) value for prism < c > slip does not depend much on the specimen size and loading‐axis orientation, with the average CRSS value of 1.66 ± 0.22 GPa. The [0001] dislocations on the prism slip planes exhibit a strong tendency to align along their screw orientation, indicating the existence of a high Peierls barrier for the [0001] dislocation in the screw orientation. The generalized stacking fault energy calculations by first‐principles density functional theory indicate that the [0001] dislocations prefer to glide as undissociated dislocations on the prism slip plane with the largest interplanar spacing, where the large empty channels (imaged as regular hexagons in the [0001] projection) are not cut. The values of fracture toughness K IC are evaluated to be 2.0–2.3 MPa·m 1/2 without apparent orientation dependence by single‐cantilever bend tests of chevron‐notched single‐crystal specimens. In addition, grain boundary sliding is found to occur at a relatively low shear stress of about 0.9–3.3 GPa during compression tests on micropillar specimens unintentionally containing a grain boundary.