Crystal Structure And Physical Properties In Deep Sr-vacant Spin-orbit-coupling Induced Mott Insulator Sr₂IrO₄

Superconductor has been widely used in power transmission,electronic communication and strong magnetic field due to its zero-resistance characteristics,diamagnetism and Josephson effects since superconductivity is discovered.However,low temperature superconductor operates in liquid helium environment,which limits the superconductivity applications.Therefore,it is necessary to find higher critical temperature of the superconducting material.The theoretical calculation predicts that the unconventional superconductivity could be realized through carrier doping in spin orbital coupling（SOC）Iridium oxide,and its critical temperature may be higher than copper oxide superconductors.Therefore,we study the crystal structure and physical properties with doping concentration in deep Sr-vacant SOC induced Mott insulator Sr₂IrO₄,which will provide scientific basis for exploring superconductivity in the material system.A series of polycrystalline samples of Sr_2-xIrO₄（x≤0.50）have been synthesized by a solid-state reaction method.The structure properties are studied by the x-ray diffraction（XRD）,Energy Dispersive X-ray Spectrometer（EDS）,Rietveld structure refinement and Raman scattering.It is shown by XRD and EDS analysis that the Sr2-x IrO4 samples with high crystallinity and accurate element ratio can be prepared.According to Rietveld structure refinement and Raman spectrum results,relative parameters of the crystal structure are changed.Apart from that,it is found that deep Sr-vacancies of Sr2-x IrO4 greatly reduce the rotation of Ir O6 octahedral,and more importantly,a significant structural change occurs around x=0.48 in both the lattice constants and the Ir-O2 bond length.In terms of physical characteristics,this thesis also focus on the electrical transport properties of Sr_2-xIrO₄ samples.The resistivity is systematically decreased as the Sr defects increase in Sr_2-xIrO₄.An insulator to metal transition appears in the transport characteristics at x=0.5,and a non-Fermi-liquid metallic electronic state has been proved for Sr1.5IrO4.In order to better elucidate the conductivity mechanism of insulated Sr_2-xIrO₄ samples,three theoretical models are used.The three dimensional variable range hopping behavior is observed in the low-temperature range,the fixed range hopping model in intermediate temperatures,and the two-dimensional weak-localization at high temperatures.The temperature dependent magnetic properties of Sr2-x IrO4 were measured.With increasing Sr-vacancies,a sudden drop of the AFM transition temperature TN and a sign reverse of the Curie-Weiss temperature,accompanied by an IMT appears in the transport characteristics at x=0.5,which is closely related with the reduction of the rotation crystal structure.These results indicate the magnetic transition from the canted-antiferromagnetic-insulating（CAF-I）to paramagnetic-metal（PM-M）ground state.