The Effects Of Fe Doping On The Structure,Electrical And Optical Properties Of Double Perovskite Dielectric Ceramics Sr₂Al_1-xFe_xNbO₆(0?x?1)

Sr₂AlNbO₆ low-dielectric ceramic material is a kind of promising substrate material for high-temperature superconducting oxide films.At present,there is little research on its physical properties,especially magnetic properties;Sr₂FeNb O₆ giant dielectric ceramic material can play a huge role in capacitors,resonators,sensors and solid oxide fuel cells.However,there are currently disputes about its crystal structure and the physical mechanism what makes that doping can significantly destroy the dielectric properties.In addition,since it can have both ferroelectricity and ferromagnetism/antiferromagnetism and spontaneously generate magnetoelectric coupling effects,multiferroic materials have great potential in microelectronics devices,especially in the emerging field of spintronics.In addition to continuously improving the physical and chemical properties of existing multiferroic materials,designing new multiferroic materials is also a very important task.In order to solve the above two types of problems,this paper conducts two experimental studies as follows.1.Sr₂Al_1-xFe_xNb O₆(0??1)series lead-free ceramic materials have been successfully prepared by the traditional high-temperature solid-phase reaction method,and their crystal structures,electronic structures and physical properties have been studied.When?0.1,the crystal structures are cubic(Fm3m);when 0.2??0.4,the crystal structures are orthorhombic(Pnma);when?0.6,the crystal structures are tetragonal(I4/m).With the increase of Fe content,on the one hand,the content of impurity phase AlNbO₄ gradually decreases,and finally disappears when?0.6;on the other hand,the order of the B-site cation decreases rapidly,and finally disappears when?0.2.Through calculation,when x=0.4,the average crystal grain size is the smallest,and the crystal structure is the most stable.Then,with the increase of Fe content,the agglomeration effect of sample particles gradually weakened,and all samples contained no other impurity metal elements.The Raman test proves that as the Fe content increases,the crystal structures of the samples undergo two phase changes.XAS and XPS spectra prove that all samples do not contain other impurity metal elements and oxygen vacancies,and the valence states of Sr,Al,Fe and Nb ions are+2,+3,+3 and+5,respectively.The P-E test shows that,Sr₂FeNb O₆ may have strong room temperature ferroelectricity,which is first discovered that Sr₂FeNb O₆ has ferroelectricity.The M-H test indicates that Sr₂AlNbO₆ has weak room temperature ferromagnetism,which is also the first discovered that the double perovskite structure oxide without any magnetic ions has ferromagnetism.The mechanism of ferromagnetism is that Al and Nb vacancies cause the nearest neighbor O 2p electrons to spontaneously produce a strong spin polarization effect.With the increase of Fe content,the relative dielectric constants of the samples gradually increase,which is caused by the crystal structure,the orbital hybridization between B-O ions,and the particle size.2.A new room temperature multiferroic material Y₂Fe Al O₆ was successfully prepared by the traditional high-temperature solid-phase reaction method,and its crystal structure,electronic structure and physical properties were studied.The crystal structures of samples Y₂Fe Al O₆(YFAO)and YFe O₃(YFO)belong to the orthorhombic system(Pnma),and YFAO has smaller lattice size,grain size,and higher crystal symmetry and stability.Raman spectroscopy verifies that YFAO and YFO have the same crystal structure,and proves that YFAO has higher crystal symmetry and longer Y-O bond length.XAS and XPS spectra prove that the Fe elements in YFAO and YFO are both a mixed state of Fe³⁺and Fe²⁺,but the relative content of Fe²⁺and oxygen vacancies in YFAO is higher.The room temperature P-E test proves that YFAO has stronger ferroelectricity.The room temperature M-H test shows that the ferromagnetism of YFAO is enhanced,but the antiferromagnetism is weakened.At the same time,it is also found that there is an exchange bias effect in YFO,but not in YFAO.And YFAO possesses stronger magneto-dielectric coupling effect.In the experiment of improving YFAO,Dy-and Gd-doped YFAO have better room temperature multiferroicity.