Growth And Physical Properties Of 5d Transition Metal Os&Ir Oxide Materials

In the field of condensed matter physics,5d transition metal oxides have been extensively studied due to the strong spin-orbit coupling,resulting in various novel quantum phenomena.These materials exhibit various interactions at the same energy scale,such as spin-orbit coupling,lattice,and Coulomb interactions.The electronic band structures of 5d transition metal oxides are often influenced by these interactions,leading to novel properties distinct from those of 3d transition metal oxides,includ-ing unconventional superconductivity,Mott insulating states,and quantum spin liq-uids.These novel properties and underlying interaction mechanisms hold great research value.In this dissertation,we explored the growth of several Os and Ir oxides,investi-gated their structures and properties,discovered phenomena such as multiferroicity and metal-insulator transitions,and discussed underlying interactions in these materials.Firstly,we successfully synthesized the osmate Ba₅（OsO₅）₃Cl,which is a rare fer-romagnetic insulator among 5d transition metal oxides,and we observed ferroelectricity in this compound.X-ray diffraction measurements confirmed the non-centrosymmetric space group of the material as P6₃cm（No.185）.Electrical conductivity tests revealed that the material is a good insulator.Magnetic measurements indicated the occurrence of ferromagnetic ordering at 5 K.The dielectric constant and polarization measurements manifested a possible ferroelectric ordered phase below 150 K.Furthermore,magnetic measurements indicated that the magnetism in the material is predominantly contributed by Os⁷⁺spin moments,with little contribution from spin-orbit coupling,which was sup-ported by theoretical calculations.Additionally,we designed a doping system Sr_1-xLa_xIr_1-xM_xO₃（M=In,Cr,and Mn）based on the orthorhombic perovskite structure of SrIrO₃and synthesized the doped samples under high-temperature and high-pressure conditions.We characterized the electrical transport and magnetic properties of these samples.Powder X-ray diffrac-tion measurements revealed that all doped samples possess the space group Pbnm（No.62）,and the lattice volume monotonically changes with the doping ratio as expected.In the In-doped and Cr-doped samples,we observed a metal-insulator like transition and antiferromagnetic ordering induced by doping,suggesting a possible correlation between the two kinds of transitions and hinting at a metal-insulator transition with a Slater mechanism in this system.Moreover,the samples doped with different magnetic ions exhibit distinct electromagnetic ground states,which require further investigation regarding the underlying mechanisms.Finally,we grew single crystals of Sr₂IrO₄using potassium hydroxide as flux and performed X-ray diffraction analysis.The structure analysis revealed that the space group of the grown Sr₂IrO₄ is Ⅰ 4/mmm（No.139）.Unlike the Ⅰ4₁/lacd（No.142）structure Sr₂IrO₄obtained through other flux methods,the IrO₆layers of Sr₂IrO₄in our work exhibit a random rotation configuration,representing a disordered arrange-ment.We also conducted physical property measurements on both single crystal and polycrystalline samples of Sr₂IrO₄.Both samples exhibit semiconductor-like behav-ior of resistivity and a weak ferromagnetic transition around 220 K.Additionally,the magnetic susceptibility and specific heat data of both single crystal and polycrystalline Sr₂IrO₄exhibit anomalies below 6 K,suggesting a possible spin reorientation in the material.In 5d transition metal oxides,the cooperative and competitive effects of crystal field,electron-electron Coulomb repulsion,and spin-orbit coupling interactions give rise to rich physical properties.Based on the successful synthesis of Ba₅（OsO₅）₃Cl,Sr_1-xLa_xIr_1-xM_xO₃（M=In,Cr,and Mn）,and Sr₂IrO₄,we characterized and analyzed their properties,discussed the mechanisms behind various interactions in these mate-rials,which provided new research systems for the exploration of correlated electron materials with strong spin-orbit coupling.