Phase Structure Optimization And Electrical Properties Of Barium Titanate-based Lead-free Piezoelectric Ceramics

Piezoelectric materials are now widely used in as daily life,such as medical care or energy transportation,etc.At present,lead zirconate titanate piezoelectric ceramics are still the main materials in practical application.It is well known that lead has great harm to human body.So various countries have put forward strict requirements for the use of Pb.For many years,the study of lead-free piezoelectric ceramics has been an important part of the research direction of piezoelectric ceramics.In 2009,Ren reported the ultra-high piezoelectricity of Ba(Ti_0.8Zr_0.2)O₃-(Ba_0.7Ca_0.3)TiO₃（BCZT）ceramics.Then,a lot of research concerning on the BCZT system has reported.As doping modification is a common method to improve the performance of piezoelectric ceramics,we have studied the A-site Sm-doping and B-site Hf-doping BaTiO₃ based piezoelectric ceramics respectively in this paper.1、Sm-doped modified 0.5(Ba_0.7Ca_0.3)TiO₃-0.5Ba(Hf_0.16Ti_0.84)O₃（BCHT）ceramics were prepared by solid state reaction.Through XRD test,it was found that all ceramics exhibited a single perovskite structure,and Sm³⁺occupied the A site in the crystal lattice and caused the lattice spacing to reduce the crystal lattice shrinkage.When the Sm³⁺doping amount is 0.1%and 0.2%mole,the coexistence of orthogonal phase and tetragonal phase in morphotropic phase boundary（MPB）structure was observed by XRD test.In the SEM images,it can be seen that small particles and large particles are stacked on each other to form a dense structure.With the increase of doping content of Sm ions,the grain size increases.When the Sm³⁺doping amount up to 0.2%mol,the remnant polarization（Pr）reaches the maximum（Pr=8.54μC/cm²）and the maximum piezoelectric coefficient(d₃₃)value is 314 pC/N.The temperature dependence of dielectric constantεr was tested and the results show that the Curie temperature is around 85°C.There are two distinct phase transition processes during the heating process.2、Hf-doped modified Ba_0.95Ca_0.05Ti_0.95-xHf_x Zr_0.05（BCZT-xHf）ceramics were prepared by solid state reaction.The effect of Hf doping amount on phase structure was detected by XRD.When⁺the Hf doping amount is 0%and 2%mole,the coexistence of rhombohedral phases and orthogonal phases MPB structure was found in the XRD pattern.When the Hf doping amount increases to 4%and 5%mol,the coexistence of orthogonal phases and tetragonal phase MPB structure was found in the XRD pattern.But when the doping amount of Hf increases to 6%mol,there results show that only tetragonal phase exists in the XRD pattern.It can be seen from the SEM image that doping of Hf leads to slow grain growth rate and reduced grain size.The Pr of the BCZT-0.02Hf ceramics reaches the maximum（Pr=6.38μC/cm²）.The maximum piezoelectricity is existed in the composition of BCZT-0.04Hf（d33=259 pC/N）.