New Structures Of Iridium-based Compounds

Transition metal elements now play a vital role in the exploration of new quantum effects.This is because 5d transition metal elements compared to traditional 3d transition metal elements have a more complicated electronic structure,the compounds have more unique novel properties,such as quantum spin liquid.Quantum spin liquids have recently become a hot topic in condensed matter physics.Its topological properties can be applied to the design of quantum computing,and its structure and properties can help explain the principles of high-temperature superconductors.A2IrO3(A=Na,Li,Cu),one of the Ir metal oxide in the 5d transition metal compound,which is a honeycomb structure similar to a-RuC13 and has a strong geometric frustration effect,and is closer to the quantum spin liquid material of Kitave model.In addition,among transition metal silicides,the transition metal silicides with the highest silicon content are found in the Ir-Si system.Such silicides are usually used in the fields of thermoelectricity and microelectronics.Plenty of literatures prove that the proportion of Si from low to high will make the dominant chemical bond in the system change from metal bond to covalent bond,which means that Ir-Si metallic compounds may have more abundant properties.Throughout the synthesis and testing of iridium-based compounds and their metastable structures,we find that their structures and properties are rarely studied under extreme high temperature and pressure.In this paper,the high temperature and high-pressure synthesis techniques of diamond on anvil and large press are used to explore new iridium-based compounds under high temperature and high pressure conditions.Diamond anvil technology can be used in situ to study the properties and structural changes of the material under high temperature and pressure,especially for some materials that cannot exist stably under high pressure.Ans the high-temperature and high-pressure synthetic experiment has obvious advantages in the synthesis of metastable materials and unconventional stoichiometric ratio compounds.In the first part,the synthesis of Cu2IrO3,the exploration of high-pressure phase and the characterization of in-situ high pressure test were mainly carried out.Cu2IrO3 polycrystalline powder was prepared by solid phase replacement reaction.The X-ray powder diffraction showed that the structure of CU2IrO3 was similar to that of Na2IrO3,delafossite derivative type,and the space-group is C2/c.Cu atom forms a barbell structure with the two O atoms around it in the honeycomb sandwich of CU2IrO3.the Ir-Ir-Ir bond Angle in the a-b plane is closer to 1200 than Na2TO3,which indicates that Cu2IrO3 has a more ideal bond Angle and is closer to the honeycomb Kitaev model.In addition to conventional low-pressure phase exploration,The structural change of CU2IrO3 from 2.5 GPa to 49.3 GPa was studied in this paper using diamond anvil cell(DAC)and in situ high pressure powder X-ray diffraction technology of synchrotron radiation source,and it was found that a new high pressure phase was generated at 20.4Gpa.The high-pressure phase of Na2IrO3 was used as the model for powder structure refine by Lebail method,and the space-group is C2/m.In this structure,the arrangement of Cu atoms in the Ir-cu sandwich does not change much.However,due to the increasing pressure,the c-axis keeps getting shorter and shorter,so the Cu and the surrounding oxygen atoms are no longer the original "dumbbell"(O-Cu-O)structure,but form a twisted octahedral structure with the surrounding six oxygen atoms.This is a brand new CU2IrO3 structure.In the second part,the high temperature and high-pressure synthesis of Ir-Si binary compounds and their characterization were studied.In this paper,the Ir-Si binary compound samples were synthesized at high temperature and pressure by using Kawai-type multi-anvil apparatus.Iridium silicides were tested by scanning electron microscopy(SEM),X-ray energy spectroscopy(EDS)and X-ray single crystal diffraction,and three Ir-Si binary compounds with different structures were found,which were IrSi2.28,Ir0.96Si1.04 and Ir1.1Sio.9,respectively.Ir0.96Si1.04 is isomorphous with s-FeSi and the space-group is P213.The average bond length(2.556 A)of the Ir-Si bond of this structure is larger than that of the traditional IrSi structure(Pnma,2.487 A),but its atomic density is larger than that of the IrSi structure,which conforms to the characteristics of the high-pressure synthesis phase.The space-group of Ir1.1Si0.9 is 14,and the average bond length of its Ir-Si bond(2.561 A)is the largest among all Ir-Si binary compounds.Because some Ir atoms occupy the positions of Si atoms.IrSi2.28 is the binary transition metal silicide with the highest proportion of silicon and resolves the disputes over the structure of IrSi?3 and the proportion of Ir-Si elements for many years.