A <sub> 2 </ Sub> B'b "o <sub> 6 </ Sub> Perovskite Oxide System, Structure, Magnetic And Electrical Transport Properties

The study of the synthetication and performance of the A₂B'B"O₆ type double peroviskite has been reported since 20th century 50's.At the end of the 90's, a series of special character such as non-conventional high temperature superconductivity and the room temperature tunneling magnetoresistance effect in this system had been discovered, thus caused the research of double perovskite oxide compound system got high attention both in experiment and the theory, and became an extremely active role of front research area in condensed matter physics.In 1997 Maokun Wu has reported a non-cuprate-planes Sr₂YRu_1-xCu_xO₆ (Tc up to 30K), which belongs to high temperature superconductor and has some interesting magnetism properties such as magnetic moments ordered at low temperature and Spin-glass behavior;In 1998 Kobayashi etc. discovered the tunneling magnetoresistance effect in Sr2FeMoO at room temperature (300K), which was as high as 10%. A₂B'B"O₆ double perovskite material was considered as one of the most applied magnetic resistance materials immediately. In theory, cause B' and B" site ions have varied electron configuration; these oxides can have more abound reforming unit, which provide theoreticians abundant model building space. In one word, the probe into the electric and magnetic property of this double peroviskite is very attractive and has extreme values.By comparing the double perovskite structure oxide with the simple perovskite structure oxide in this thesis, we first reviewed the research achievements of A₂B'B"O₆ and new progress; then we synthesized Ba₂YRu_1-xCuxO₆ and Sr₂FeRuO₆ with solid-state reaction method. Then we chiefly studied their structure and magnetic propertied of the Ba₂YRu_1-xCu_xO₆ and the magnetic properties and magnetoresistance effect of the Sr₂FeRuO₆. Main results of my work are shown as following:First, we synthesized single-phase Ba₂YRu_1-xCu_xO₆ double perovskite structure oxide successfully when x is smaller than 0.15. The samples are found to be of a cubic lattice cell with a=8.345 A (x=0). It shows much difference with x changing., where Y³⁺ and Ru⁵⁺ ions occupy the 4a(0,0,0)and 4b(1/2, 1/2, 1/2)equivalent atomic positions respectively. The Bragg reflection (111) was identified to be a characteristic feature for an order distribution of Y³⁺ and Ru⁵⁺ ions. The electrical resistivity of the sample has been measured by standard four-probe technique in a temperature range from 10 K to 300 K. Ba₂YRuO₆ is found to exhibit the typical electrical transport behavior of an insulator with a large resistance; Cu doping considerably lower the resistance of the sample ,a transition from an insulator to semiconductor caused by Cu doping was observed in Ba₂YRu_1-xCuxO₆ (x=0, 0.1, 0.15) double perovskite system. The magnetization curve at room temperature had been measured by Vibrating Sample Magnetometer (VSM) technique. The results indicate that all samples exhibit the typical paramagnetic behavior with an effective magnetic moment P_eff -2.06μB for each Ru atom (x=0),and it decrease as x increased.Second, Sr₂FeRuO₆ has been synthesized successfully and Rietvelt refinement indicates that Sr₂FeRuO₆ is of an ordered double perovskite structure with a tetragonal cell which a=b=5.528 A, c=7.822 A,space group is I4/mmm.The result indicated the oxygen octahedron of the Sr₂FeRuO₆ double perovskite structure slightly has the stretch in the c axis direction, so Fe³⁺ ion ([ Ar ] 4d5) and the Ru5+ ion ([ Kr ] 4d³) present the slight John Teller effect. Its magnetization curve indicates that Sr₂FeRuO₆ is antiferromagnetic with its Neel temperature far above room temperature. Its resistivity-temperature curve suggests that Sr₂FeRuO₆ exhibits typical semiconductor behavior with an estimated energy gap Eg⁰.23 eV, and the sample can get 20% magnetoresistance effect at 120K, through the synthesis condition improvement, esistivity further reduces ,we hope to enhance its magnetoresistance.