Prediction of scandium tetraboride from first-principles calculations:Crystal structures,phase stability,mechanical properties,and hardness

Using the evolutionary methodology for crystal structure prediction,we have predicted the orthorhombic Cmcm and Pnma phases for ScB_(4).The earlier proposed Cr B_(4)^(-),Fe B_(4)^(-),Mn B_(4)^(-),and Re P_(4)^(-)type structures for ScB_(4)are excluded.It is first discovered that the Cmcm phase transforms to the Pnma phase at about 18 GPa.Moreover,both phases are dynamically and mechanically stable.The large bulk modulus,shear modulus,and Young's modulus of the two phases make it an optimistic low compressible material.Moreover,the strong covalent bonding nature of ScB_(4)is confirmed by the ELF analysis.The strong covalent bonding contributes greatly to its stability.

Ground-state structure and physical properties of YB_(3) predicted from first-principles calculations

Using the calypso algorithm with first-principles calculations,we have predicted two orthorhombic Cmmm and Pmmm structures for YB_(3).The new structures are energetically much better than the previously proposed WB_(3)-type,ReB_(3)-type,FeB_(3)-type,and TcP3-type structures.We find that the Cmmm phase transforms to the Pmmm phase at about 31 GPa.Subsequent calculations show that the Cmmm phase is mechanical and dynamical stable at ambient conditions.The analysis of the chemical bonding properties indicates that there are strong B-B bonds that make considerable contributions to its stability.

Ground State Structures of Boron-Rich Rhodium Boride: An Ab Initio Study

A new phase of RhB4is predicted based on first-principles calculations. The new phase belongs to the orthorhombic Pnnm space group, named as o-RhB4, and analysis of the calculated enthalpy shows that o-RhB4belongs to the orthorhombic Pnnm space group. The calculated phonon band structure shows that the orthorhombic Pnnm o-RhB4structure is stable at ambient pressure. We expect that the phase transition can be further confirmed by experiments.