The Preparation And Properties Of B Site Doped BNT-based Lead-free Piezoelectric Ceramics

Piezoelectric ceramics are widely used in communication,medical treatment,military and so forth,but most of them contain about 60 wt% Pb element.Concerning environment and health,it is urgent to find some lead-free piezoelectric materials to replace Pb-based materials.Due to the excellent ferroelectric property,Bi_0.5Na_0.5TiO₃?BNT?-based piezoelectric ceramics are considered to be the most promising alternatives to substitute for lead-based piezoelectric ceramics.In this paper,BNT-based as the researched subjects,we successfully prepared B site single ion modified and B site complex ions modified BNT-based ceramics samples by solid-state reaction and the effect of doping modification on phase structure,ferroelectric,piezoelectric,strain response properties and so on were studied.0.8BNT-0.2SBT system as the base material,0.8BNT-0.2SBT-x Nb ceramics samples were fabricated.x = 0.01 samples were the single perovskite structure.However,for x = 0.02 and 0.03,there were an obvious secondary phase peak.With the increase of Nb⁵⁺ doping,the d33* increased from 229 pm/V to 390 pm/V,d33 reduced from 146 p C/N to 7 p C/N,and TF-R decreased from 120 ? to 40 ?.These showed that the long-range order was disturbed and ergodic relaxor phase formed,which could be transformed into ferroelectric phase under applied electric field?AEF?,bringing a large strain.The properties of 0.8BNT-0.2SBT-x Nb samples were the result of the combined action of composition,temperature,electric field,etc.0.8BNT-0.2BKT and 0.884BNT-0.08BKT-0.036 BT system as matrix materials,B site(Fe_0.5Nb_0.5)⁴⁺ complex ions doped 0.8BNT-0.2BKT and 0.884BNT-0.08BKT-0.036 BT ceramics samples were prepared.All(Fe_0.5Nb_0.5)⁴⁺ doped samples were single perovskite structure.With the increase of the(Fe_0.5Nb_0.5)⁴⁺ content,ferroelectric order was gradually disturbed and TF-R gradually reduced to room temperature,causing a ferroelectric to relaxor phase transition.And under the AEF,phase transition from ergodic relaxor phase to ferroelectric phase could be happened,bringing a dramatical increase in strain.When(Fe_0.5Nb_0.5)⁴⁺ content was 0.04 and 0.055,respectively,large electric-field-induced strains 0.40%@6.5 k V/mm?d33* = 613 pm/V?and 0.36%@6 k V/mm?d33* = 600 pm/V?were obtained at room temperature.0.91BNT-0.06BT-0.03 KNN system as the base material,Cu²⁺ doped 0.91BNT-0.06BT-0.03 KNN ceramics samples were manufactured.Cu²⁺ doping reduced the sintering temperature from 1150 °C to 960 °C,and improved the density of samples.All Cu²⁺ doped samples were single perovskite structure and possessed ergodic relaxor phase structure at room temperature.With the increase of Cu O content,dielectric constant????Curie temperature?TC??strain?S?and polarization?P?decreased first and then increased,while the coercive field?EC?first increased and then decreased.The piezoelectric coefficient of Cu²⁺ doping ceramics samples were less than 30 p C/N due to the poor piezoelectric response of ergodic relaxor phase.The maximum strain of samples doped with Cu²⁺ were 0.381%?0.313%?0.330%?0.335% at 7 k V/mm AEF,respectively.