Theoretical Studies On Physical Properties Of Cobalt Triphosphide Crystal Structure Under High Pressure

Due to its excellent thermoelectric properties,skutterudite with chemical for-mula MX₃（M=Co、Rh、Ir,X=P、Sb、As）have been widely paid attention.Herein,the method based on density functional theory and particle swarm crystal structure search technology will be used to predict the structure of CoP₃in the range of 0-100 GPa.The physical properties of the predicted new high pressure phase were studied.Studies have shown that under high pressure,The crystal structure of CoP₃takes place the structural phase transition for four times,which is a first-order phase transition.The phase transition sequence is Im（?）（αphase）-→P nma（βphase）-→C₂/c（γphase）-→C₂/m（δphase）.The phonon dispersion relationship is calculated for each phase crystal structure of CoP₃,In order to determine the stability of the new phase,phonon dispersion relations were calculated for the crystal structure of each phase of CoP₃.The results show that no virtual frequency appears in the whole Brillouin zone,indicating that the crystal structure of the high pressure phase predicted has dynamic stability.The study of formation enthalpy shows that the formation enthalpy of all phases of CoP₃is negative.This indicates that the crystal structure has thermodynamic stability.The electronic energy band,density of states and bonding properties of the predicted atmosphericαphase,the high pressureβphase,theγphase and theδphase have been studied.The results show thatαphase,βphase andγphase all exhibit indirect band gap semiconductor properties,andδphase exhibits metallic properties.The study of electron density of states shows that the predicted phase structure of CoP₃near the valence band is mainly contributed by the d orbital of Co atom and the p orbital of P atom.Bader charge transfer calculations show that the charges ofα,β,γandδphases are transferred from P to Co atoms.By calculating the electron local function,it is shown that there are polar covalent bonds between Co and P atoms in each phase of CoP₃,and covalent bonds between P and P atoms.The study of electron transport properties shows that the predicted p-typeβphase has a higher Seebeck coefficient.Through the calculation of elastic properties,all phases of CoP₃have good brittleness.By studying the structure of CoP₃crystal under high pressure,we found high pressure structures with excellent physical properties.It provides an important reference for the study of binary skutterudite under high pressure.