Dominant in-plane cleavage direction of CrPS ₄

In-plane cleavage directions of two-dimensional (2D) crystals are displayed and often well defined in their flakes exfoliated by the mechanical exfoliation method. Here, we investigate the correlation between dominant in-plane cleavage direction and elastic properties in different directions for CrPS ₄ . CrPS ₄ flakes show a preferential in-plane cleavage direction of 67.5° corresponding to 〈1 1 0〉 direction. To explain it, we calculated the directional dependence of Young's modulus and fracture energy using first-principles density functional theory calculations. We found that relative fracture energy is directly relevant to the in-plane cleavage direction of CrPS ₄ . It is also found that in CrPS ₄ the rhomboidal Cr–S–Cr bonds, which are especially vulnerable in 〈1 1 0〉 direction, connect robust structural motifs to each other. Our study can provide a facile approach to figure out the direction of 2D crystals without complex characterization process, which is valuable for material processing of 2D materials.