Modulation On Structure And Dielectric Properties Of Bi-layer Structured Piezoelectric Ceramics

Bi-layer structured piezoelectric ceramics are kind of important piezoelectric and ferroelectric materials,which generally exhibit excellent fatigue resistance,high Curie temperature,low dielectric loss,good electrical performance and temperature stability,and are often used in Ferroelectric-Random Access Memory and high temperature and high frequency piezoelectric components.However,due to the special crystal structure of Bi-layer structured piezoelectric ceramics,its dielectric constant is generally low.Some Bi-layer structured piezoelectric ceramics have dielectric relaxation characteristics due to their structural characteristics,but the research on the dielectric relaxation characteristics of ceramics is still incomplete.In addition,most ceramics with high Curie temperature exhibit low piezoelectric coefficients,which hinders the applications in high temperature piezoelectric fields.In this paper,the dielectric and piezoelectric properties of BaBi₄Ti₄O₁₅?BBT?based piezoelectric ceramics are improved by using the traditional solid-state sintering process,through the modification of A,B and A/B ions.Ba_1-xNd_xBi₄Ti₄O₁₅?BNBT?and BaBi_4-xNd_xTi₄O₁₅?BBNT?ceramics are prepared by using the convention solid-state reaction method.Effect of neodymium substitution on the structural and dielectric properties of the BaBi₄Ti₄O₁₅?BBT?ceramic are investigated.A broaden dielectric peak in frequency dependent dielectric spectrum is observed during the phase transition of all the neodymium substituting BBT ceramics.The modified Curie-Weiss and Lorentz-type relationship are used to describe the phase transition behavior.Contribution of the dopant substituting positions on the structural and electrical properties of the BBT ceramics are discussed by investigating the effect of neodymium substitution on the parameters?,?_A and?35?T_Relaxor of the empirical relations.For improving the dielectric properties of BBT ceramics,BaBi_4-xTi_4-x(Cu_1/3V_2/3)_2xO₁₅?BBT-Cu V,x=0.00,0.03,0.06 and 0.09?ceramics are prepared by using the conventional solid-state reaction method.BBT-Cu V ceramics are prepared by using Cu²⁺and V⁵⁺on the B site co-doped BBT ceramics.Effects of Cu²⁺and V⁵⁺on the crystal structure,micromorphology and dielectric properties of BaBi₄Ti₄O₁₂?BBT?ceramics are investigated.Curie temperature and dielectric constant of BBT ceramics are improved by the copper and vanadium modification.The maximum of dielectric constant was found to be 325?at low frequency 100 Hz?for BBT-9Cu V ceramic,together with high Curie temperature?T_c?466??.To further improve the dielectric properties of BBT ceramics in the low frequency region,Ba_1-x(K_0.5Bi_0.5)_xBi_3.91Ti_3.91(Cu_1/3V_2/3)_0.18O₁₅?BBCVT-KBi,x=0.00,0.25,0.50 and 0.75?ceramics were prepared by using the conventional solid-state reaction method.The bimodal distribution of grain size is observed in K⁺/Bi³⁺co-doped BBCVT ceramics.Effects of K⁺and Bi³⁺on the structures,morphologies and electric properties of BBCVT-KBi ceramics are investigated.Dielectric permittivity of the BBCVT ceramic is enhanced dramatically by potassium and bismuth modification and giant dielectric permittivity?>10⁴ at 100 Hz?can be observed in the BBCVT-75KBi ceramic.Moreover,reasons of giant permittivity at low frequency in BBCVT-KBi ceramics are systematically discussed.For investigating the effects of lattice distortion and defects on the cations modified piezoelectric ceramics.BaBi₄Ti_4-x(Cu_0.5W_0.5)_xO₁₅ ceramics with Cu²⁺and W⁶⁺co-substitution for the B-site Ti⁴⁺are prepared by using the solid-state reaction process.It was desirable that piezoelectric properties of the BaBi₄Ti_4-x(Cu_0.5W_0.5)_xO₁₅ ceramics could be improved by inducing the larger lattice distortion with the oxygen vacancy defects neutralized and restrained.Results of the X-ray diffraction analysis confirmed that crystal cell parameter c decreased obviously with the increase in the crystal cell parameter a.Curie temperature,resistivity and piezoelectric properties of the BBT ceramics are improved by the copper and tungsten modification.The maximum value of piezoelectric coefficient??30 p C/N?can be obtained in the BaBi₄Ti_4-x(Cu_0.5W_0.5)_xO₁₅ ceramics.