Preparation And Transport Properties Of Room Temperature Ferromagnetic Sr₃YCo_4-xCu_xO_10.5+δ (0≤x≤0.4

Sr3YCo4O10.5+δ is a complex layered Co oxide with perovskite structure,in which CoO6 octahedra layer and oxygen-deficient CoO4+δ layer are alternately stacked along the c axis.Sr and Y are ordered in the ab plane,and are stacked along the c axis with a periodicity like-Sr-Y-Y-Sr-.Sr3YCo4O10.5+δ polycrystalline shows ferromagnetic transition at 33 5K,which is the highest Curie temperature among all known Co oxides.The unusual room-temperature ferromagnetism originates from the oxygen vacancy and Sr/Y ordering.Besides,Sr3YCo4O10.5+δ can be used as cathode material for solid oxide fuel cells(SOFC),ceramic membranes for high temperature oxygen separation and catalysts for oxygen reduction electrodes in alkaline fuel cells due to the high electronic and ion conductivity as well as high catalytic activity.The paper on the one hand focuses on the process for the preparation of Sr3YCo4-xCuxO10.5+δ(0≤x≤3.0)polycrystallines,on the other hand preliminary discusses the effects of Cu substitution for the Co on the electrical properties,thermopower and magnetic property of Sr3YCo4O10.5+δ polycrystalline.Finally,Sr3YCo4O10.5+δ thin films have been grown on the LaAlO3(100)and SrTiO3(100)substrates by plused laser deposition,respectively.Sr3YCo4O10.5+δ and Sr3YCo4-xCuxO10.5+δ(0≤x≤3.0)polycrystallines have been prepared in the air by solid state reaction method with the sintering process of 1180℃/24h and 1100℃/24h,respectively.The experimental results indicate that the maximum Cu doping content is 0.4 to keep Sr3YCo4O10.5+δ being single phase.Sr3YCo4-xCuxO10.5+δ polycrystalline with tetragonal structure shows typical porous microstructure.The resisitivity and thermopower of Sr3YCo4O10.5+δ at room temperature are 0.36Ωcm and 72μV/K,respectively,and the electrical property and thermopower are semiconducting behavior.At the same time,Sr3YCo4O10.5+δ exhibits room-temperature ferromagnetism at TC～335K.As the Cu content is increased,the resistivity,thermopower and Curie temperature of Sr3YCo4-xCuxO10.5+δ decrease.Analyses indicate that Cu-doping results in the growth of grain particles and the increase of carriers,leading to the decrease of resistivity and thermopower.And the ferromagnetic ordering is suppressed and Co3+occurs from intermediate spin state to low spin state after Cu substitution for Co,resulting in Curie temperature shifting to lower temperature.Sr3YCo4O10.5+δ thin films have been successfully grown on the LaAlO3(100)and SrTiO3(100)substrates by plused laser deposition technique.The optimal process for preparation Sr3YCo4010.5+δ thin films on LaAlO3(100)substrates has been found,which is with temperature of 790℃,deposition oxygen pressure of 100Pa,pulse energy of 280mJ,annealing temperature of 790℃,annealing oxygen pressure of 1×104Pa and frequency of 4Hz.And the optimal process on SrTiO3(100)substrates is with temperature of 760℃,deposition oxygen pressure of 1Pa,pulse energy of 400mJ,annealing temperature of 790℃,annealing oxygen pressure of 4×104Pa and frequency of 4Hz.The temperature dependence resistivity curve shows that Sr3YCo4O10.5+δ thin films are semiconducting behavior.