Research Of Microstructure, Electrical Properties And Dielectric Properties Temperature Stability On A-site Composite (Li_0.5Nd_0.5)²⁺ Irons Substitution For0.95Bi_0.5Na_0.5TiO₃-0.05BaTiO₃

The A-site composite ions substitute for0.95(Bi0.5Na0.5)1-x(Li0.5Nd0.5)xTiO3-0.05BaTiO3lead free piezoelectric ceramics (abbreviated as BNTLNx-BT5) have beenfabricated by solid-state method. The effect of composite (Li20.5Nd0.5)+ions substitute for(Bi20.5Na0.5)+ions in A-site for0.95Bi0.5Na0.5TiO3-0.05BaTiO3ceramics on structure,morphology, dielectric and piezoelectric properties was investigated and the complicatedmechanisms of composite (Li20.5Nd0.5)+ions substitute for (Bi20.5Na0.5)+ions in A-site arealso explored and discussed. There are some main innovative points and results, asfollows.The effect of composite (Li20.5Nd0.5)+ions substitution on microstructure, dielectricand piezoelectric properties for BNTLNx-BT5ceramics (x=0、0.01、0.03、0.05、0.07、0.1) was investigated. The results of XRD showed that the BNTLNx-BT5ceramicspossessed a coexistence region (morphotropic phase boundary MPB) with rhombohedralsymmetry and pseudocubic symmetry at x=0.01~0.05. The results of SEM showed thatthe partial content of (Li20.5Nd0.5)+ions can increase grain-size. The grain-size of samplesreached a maximum (~9μm) at x=0.07. The partial content of (Li20.5Nd0.5)+substitutioncan induce dielectric dispersion coefficient γ increase. The largest dispersion coefficient(γ=1.90) and a largest piezoelectric constant (d33=135pC/N) were obtained at x=0.07. Thecomposite (Li0.5Nd0.5)2+ions substitution leaded to the dielectric constant εrand dielectricloss tanδ of BNTLNx-BT5ceramics both increased gradually.The effect of poling electric field Epolon crystalline structure of BNTLNx-BT5bulksand powder was investigated. The poling electric field Epolinduced domains to beordered and induced pseudo-macrodomains to generate, which leaded to the intensity ofdiffraction peak change and diffraction peak split. The effect of electric field Epol(10~80kV/cm) on crystalline structure, piezoelectric and dielectric properties ofBNTLN0.01-BT5ceramics was investigated systematically. At Epol=20kV/cm, the XRDof samples showed the peak intensity ratio of (003)/(021) diffraction peak is above1andpiezoelectric constant d33reached a maximum (d33=124pC/N) as a mass of nano-domainswere combined into ordered pseudo-macrodomains. At Epol≥30kV/cm, the peak intensityratio of (003)/(021) diffraction peak and d33both decreased slightly. At room temperature,dielectric frequency dependence decreased with increasing electric field Epol. Theincrease of Epolinduced size of domains increase, which leaded to the dielectricfrequency dependence as a function of temperature decreased.The effect of sintering temperature Tson crystalline structure, morphology,piezoelectric and dielectric properties of BNTLN0.03-BT5ceramics was investigated systematically. The results showed that the samples possessed rhombohedral symmetry atTs=1070~1100oC and possessed pseudocubic symmetry at Ts=1130~1160oC. TheBNTLN0.03-BT5ceramics sintered at Ts=1130oC possessed the optimal piezoelectricproperties (d33=140pC/N，kp=0.30，Qm=218，kt=0.55). With increasing Ts, the dielectricconstant and dielectric loss both increased relaxedly. Furthermore, the frequencydependence of the dielectric constant as a function of temperature decreased at the25oC≤T≤200oC. The dispersion coefficient γ of samples increased with increasing Ts.The effect of annealing temperature Ta(Ta=25、800、850、900、950、1000oC) onstructure, piezoelectric and dielectric characteristic of BNTLN0.03-BT5ceramics wasinvestigated. The poling samples annealed at Toa=900C possessed a maximum degree(K=69.41%) of90odomains rearrangement along the direction of the electric field andoptimal piezoelectric properties (d33=148pC/N，kp=0.33). The samples annealed atTa=900oC possessed a lowest depolarization temperature (Td=71oC) and a largestdisappeared temperature Th=430oC at where irreversible change of nonergodicity wasannihilated. The dielectric dispersion degree reached a maximum (γ=1.99) at Ta=900oC.