First-principles elastic stiffness of LaPO4 monazite

In this letter, the full set of elastic coefficients of LaPO4 monazite is presented based on the first-principles plane-wave pseudopotential total energy method. Mechanical parameters (bulk modulus, shear modulus, Young’s moduli, and Poisson’s ratio) are also presented and compared with experimental results for polycrystalline monazite. The responses of electronic structure and chemical bonds to a series of {010}⟨001⟩ shear strains are examined in order to study the mechanism of low shear strain resistance. The results show that small shear moduli originate from the inhomogeneous strengths of atomic bonds. For example, the weak La–O bonds accommodate the shear strain locally, while the PO4 tetrahedra are almost rigid. The theoretical elastic stiffness may be useful to understand the deformation mechanisms of LaPO4 monazite.