The Structure And Elasticity Of CaO₃ Under High Pressure Investigated By First-principles Simulation

CaO₃ is a newly discovered mineral that probably exist in the mantle transition zone and the lower mantle.Many of its basic physical properties are still unknown.To investigate the physical properties is favor of understanding the mineral composition and physical variations of the mantle transition zone.In this paper,the basic structure,electrical properties,elasticity,wave velocity and anisotropy of the newly discovered mantle mineral,CaO₃ are obtained under 10-50 GPa by first principles simulation to understand its effect on the composition and structure of the mantle transition zone.Crystal structure and phonon frequencies under 0-50 GPa indicate that CaO₃ can exist stably under 10-50 GPa.The main research results are as follows:1.based on the previous calculation results and experimental conclusions,the CaO₃ crystal model is reconstructed.The unit cell parameters,phonon spectra and density under high pressure were calculated.It is found that the crystal structure is unstable when the pressure is less than 10 GPa,and decomposition reaction may occur.Under the pressure of mantle transition zone,the density of CaO₃ crystal is lower than that of common minerals in mantle transition zone.This means that the CaO₃ crystal may play a role in regulating the density of the lower mantle in the mantle transition zone.2.Under the 10 to 50 GPa,the band gap of CaO₃ crystal is found to be 2.32 to2.77,indicating its semiconductor properties.It is found that the mineral may exhibit transition metal like properties through the obvious wave crest of mineral d orbital in the density of states.At the same time,Mulliken population analysis shows that Ca-O bond is ionic bond,O-O bond is covalent bond,and the strength of O-O bond is higher than that of Ca-O bond.The density,volume and shear modulus of CaO₃ increase with the increase of pressure;The compression wave velocity（VP）and shear wave velocity（VS）of CaO₃ increase with the increase of pressure,and the wave velocity is lower than that of the preliminary earth reference model（PREM）and common mantle transition zone minerals,which means that cao3 crystal may be a candidate mineral in the low wave velocity mantle transition zone.3.The anisotropy of Vs and Vp are respectively 36.47%,26.41%,23.79%,18.96%and 18.37%,13.91%,12.75% and 10.64% under 15,25,35 and 50 GPa.Those seismic velocity anisotropies are larger than the main composition of the mantle transition zone;so it may be an important source of seismic wave velocity anisotropy in the mantle transition zone.The results provide the new evidence for understanding the material composition and the source of anisotropy in the mantle transition zone.