Synthesis And Characterization Of Dion-Jacobson Layered Perovskites Novel Materials

Layered perovskite oxides are important functional materials in which many novel phenomena have been observed,such as high temperature superconductivity,colossal magnetoresistance,ionic conductivity,photocatalysis and ferroelectricity.Due to the difficulties of synthesis,proton conductivity and hygroscopicity,Dion-Jacobson?DJ?phases oxides have not been widely studied in crystallographic structure and physical properties,especially in ferroelectricity.In this paper,the synthesis of double layered and three layered Dion-Jacobson series of new layered perovskite oxide materials was investigated and their properties were successfully characterized.The main results are as followed:?1?Double layered Dion-Jacobson phase perovskite oxide CsSmNb₂O₇ and CsSmTa₂O₇were successfully prepared by solid state reaction.The X-Ray diffraction data show both two new samples are single phases with good qualities.X-ray crystal diffraction analysis showed that the two new material samples have a polar structure with space group of P2₁am.Observed by scanning electron microscopy,the morphology of the samples was lamellar.EDS energy spectrum analysis show that the atomic ratios of the samples are close to stoichiometry.Second harmonic generation?SHG?measurements show that 800 nm laser irradiation on the surface of the sample reflects light at 400 nm,which suggests that the two new materials are noncentrosymmetric structures.The ferroelectric test results show that all of the hysteresis loops exist vesica shape and unsaturated properties,which is typically due to the leakage current in samples.The dielectric constant is very high at low frequency and has a dielectric dispersion phenomenon.The magnetic results show that the two materials are paramagnetism.?2?A three layered DJ phase perovskite material CsBi₂Ti₂NbO₁₀0 was successfully prepared by referring to the preparation method of double layered of DJ phase perovskite.On the basis of the successful preparation of CsBi₂Ti₂NbO₁₀,the A',A and B elements were replaced by rare earth elements and ferromagnetic elements,in an attempt to explore the ferroelectric and magnetic properties.Three new DJ phase perovskite materials CsNd₂Ti₂TaO₁₀,CsSm₂Ti₂TaO₁₀0 and RbNd₂Ti₂NbO₁₀0 were successfully prepared.The optimal sintering conditions were as follows:1000?,24 h.Using the Rietveld refinement method to fit the powder X-ray diffraction data of three new materials,the results show that these new three layered DJ phase perovskite materials have the P4/mmm space group and are the highly symmetric tetragonal system.No observed SHG signal further confirms that these materials belong to a central symmetric nonpolar structure.Ferroelectricity test results also show that no ferroelectricity properties has been observed in these three materials.The dielectric constants show a dielectric dispersion phenomena.The magnetic data indicate that the CsNd₂Ti₂TaO₁₀,RbNd₂Ti₂NbO₁₀0 samples exhibit antiferromagnetic properties,while the CsSm₂Ti₂TaO₁₀0 sample containing Sm³⁺are paramagnetic.Through the above experiments,we successfully synthesized double layered and three layered new DJ phase perovskite oxide materials,and carried out structural refinement and physical property characterization.The results show that the space group of n=2 layers of DJ phase new materials are P2₁am,polar structure and ferroelectricity although current leakage is serious.These n=3 layer DJ phase new materials have centrally symmetric P4/mmm space group,nonpolar structure and no ferroelectricity;The magnetic measurement results show that the samples containing Sm³⁺are paramagnetic,while the samples of ANd₂Ti₂BO₁₀?A=Cs,Rb;B=Ta,Nb?are antiferromagnetic phase.