Preparation And Electrical Properties Of Sodium Bismuth Titanate Based Ceramics

Piezoelectric materials have been widely studied in modern science and technology which have become one of the hot research materials at home and abroad.PbZr_xTi_?1-x?O₃?PZT?based compounds have been studied by many scholars due to their superior piezoelectric properties and temperature stability.However,PZT materials contain lead toxicity,which will cause serious environmental problems.Environmental and human health concerns about lead toxicity have prompted the development of lead-free piezoelectric ceramics.Barium strontium titanate?BNT?lead-free piezoelectric ceramics with trigonal structure at room temperature.In recent years,many groups have performed A-site and B-site doping BNT in order to lower the transition temperature from cubic phase to tetragonal phase.By lowering the transition temperature,a wider tetragonal phase boundary region was obtained near room temperature to improve temperature stability of the material.At present,the pure barium titanate sodium ceramic has a large coercive field at room temperature and a high conductivity in the ferroelectric phase region,which makes it difficult to be polarized.In order to improve the properties of BNT base materials,the following studies are carried out,that is,the substitution of different elements in the A-and B-sites in BNT-based materials.Using the conventional solid-state reaction,the following systems were prepared:(Bi_0.5Na_0.5)_1-xYb_xTiO₃?BNT-xY,x=0,0.015,0.03,0.05,0.08?,(Bi_0.5Na_0.5)Yb_0.05Ti_1-xZr_xO₃?BNT5Y-xZ,x=0.05,0.07,0.1,0.13?and(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)-xTa₂O₅?BNT6BT-xT,x=0,0.005,0.01,0.02?Lead-free piezoelectric ceramics.In this work,the relationship among the composition,structure and properties of BNT-based ceramics were investigated through in the study of XRD,Raman,scanning electron microscopy,dielectric properties,and ferroelectric properties.The main results as follows:?1?The(Bi_0.5Na_0.5)_1-xYb_xTiO₃ system was studied by the traditional solid-state reaction.Through Rietveld refinement,it found that Yb occupied A-site of BNT.The sample has a good temperature stability over a wide range above 120°C when x=0.05.Furthermore,the dielectric constant varies range within 10%from 119°C to 435°C,and the dielectric loss is less than 0.025 with a temperature range of 127²45°C.?2?Lead-free piezoelectric ceramics with(Bi_0.5Na_0.5)_0.95Yb_0.05Ti_1-xZr_xO₃ system were synthesized,in which doped with Yb ions at A-site and doped with Zr ions at B-site.With increasing Zr⁴⁺content,the dielectric loss remains stables and dielectric constant increases with good temperature stability.The doping of Zr inhibits the migration of oxygen vacancies in the sample.?3?Lead-free piezoelectric ceramics with(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)-xTa₂O₅system were prepared.As the Ta content increased,the dielectric constant decreased gradually,and the transition temperature from ferroelectric phase to antiferroelectric phase increased.when x=0.02,the maximum dielectric constant is maintained at about 4000,and the dielectric loss is less than other samples from room temperature to 200°C.The doping of Ta⁵⁺extends the antiferroelectric region of the sample,so it makes the material very soft.