The First Principle Study Of Properties In Iron Chalcogenide Superconductor

Since the discovery of iron-based superconductor,especially,the first 122-like superconductor was discovered that has aroused the wide attention for studies of high temperature superconductivity mechanism.However,the mechanics of iron-based superconductors have not been fully understood so far.Unlike the conventional superconductors,iron-based superconductors are layered compounds,containing magnetic iron which is considered against superconducting and the parent compounds have complex Fermi surface structure.Here,based on the exploration of iron-based superconductor electronic properties,we study the structure properties,electronic properties and mechanical properties of the 122-like materials,using first principles calculation.First of all,we have calculated the structure properties,electronic properties and the elastic properties for the three kinds of materials under no pressure.Our results show that in the whole crystal,the anion replacements for KFe2Ch2(Ch = S?Se?Te)phases lead to anisotropic deformations both of the [Fe2Ch2] blocks and the whole crystal,but do not result in any critical changes in the near Fermi electronic bands.Among KFe2S2,KFe2Se2 and KFe2Te2,the Te-Fe-Te bond angles of KFe2Te2 are the closest to the ideal tetrahedron angles under no pressure,whereas the Te-Fe-Te bond angles are deviating from the ideal value with the pressure increasing.By calculating the electronic properties,we find that three kinds of materials' Fermi level are similar,such as crossed by four energy bands.At the same time,there is no energy gap near the Fermi surface which indicates that the electrical conductivity of this phase should be metallic-like and its Fermi surface is dominated mainly by iron 3d orbitals.By calculating the mechanical properties,the results show that three kinds of materials show considerable elastic anisotropy.In addition,our data reveals that KFe2S2,KFe2Se2 and KFe2Te2 are relatively soft materials,which are same as other related superconductor systems.And also,the phase of KFe2S2,KFe2Se2 should be brittle,whereas KFe2Te2 behaves ductile.Secondly,we have calculated the crystal structure properties,electronic properties and the elastic properties for the three kinds of materials under high pressure.Three kinds of materials' structure appear different changes under high pressure.Different from KFe2S2 and KFe2Te2,the Se-Fe-Se bond angles of KFe2Se2 are the closest to the ideal tetrahedron angles at 30 GPa,whereas the other two kinds of materials S-Fe-S and Te-Fe-Te bond angles are deviating from the ideal value with the pressure increasing.By comparing of the three kinds of materials under pressure,we found that KFe2Te2 is more sensitive to pressure than the other two kinds of materials,so we can achieve the required applications by changing the pressure.By calculating the elastic constants of KFe2S2,KFe2Se2 and KFe2Te2 under pressure,we find that the ductile manners of KFe2Ch2(Ch = S?Se?Te)are better at high pressure.The pressure can improve the stiffness and make the materials become more and more difficult to be compressed.At the same time,pressure can increase elastic anisotropy.Exploring the mechanics of iron-based superconductors have become the research focus,especially the research of Fermi surface,the Ch-Fe-Ch bond angles and Fe-Ch bond length.And also,studying of these factors under pressure has been an important way to predict superconducting transition temperature theoretically.As we all know,iron-based superconductors are layered compounds,which have the interaction between the ions in the layers and the weak couple interaction between the layers and the layers.The effects of crystal structure influencing the iron-based superconductors are based on these interactions.So exploring the different crystal structure under atmospheric pressure and high pressure is very important to explore the common characteristics of iron-based superconductors.