| With the development of science and technology and the improvement ofhuman living standards, all kinds of portable electronic devices become moreand more popular. Therefore, the miniaturization, integration and intelligent ofelectronic device will become the future develop trend of electronic industry. Inour daily life, the widely used multilayer ceramic capacitor, high Curietemperature PTC ceramics, excellent piezoelectric devices, most of themcontain Lead; however, the volatile and toxicity of Lead at high temperature doharm to people and the environment harmony in the production and use. Thus, itis urgent to develop a kind of excellent electric properties lead-free materials toreplace it. In this paper, we prepared theBaTiO3/K0.5Bi0.5TiO3ceramics withBaNb2O6addition, and the experimental results on the composition, preparationprocedure and electric properties were studied. It aimed to find a newformulation and preparation process of Lead-free functional ceramics mateials.Firstly,BaTiO3ceramics withBaNb2O6addition were prepared by aconventional solid state reaction route. The effect ofBaNb2O6addition onsintering temperature, phase composition, microstructure and dielectricproperties ofBaTiO3ceramics were investigated. The research results showthat a systematic structure change from the ferroelectric tetragonal phase topseudo-cubic phase was observed near1mol%. Nevertheless, when the contentofBaNb2O6is beyond1mol%, a small amount of secondary phase can bedetected, and this indicated that the solid solubility ofBaNb2O6inBaTiO3lattice was less than1mol%. The BaNb2O6additive might diffuse into theBaTiO3grains even deeper, and enhanced the inhomogeneity of the ceramics，leading to the reduction of the volume ratio of the ferroelectric core to theparaelectric shell region, so the dielectric constant at Curie temperature ismarkedly depressed and broaden, which improved the stability of the dielectricconstant. When the content ofBaNb2O6is0.8mol%and1mol%, the Ceramicpresented a high dielectric constant, low dielectric loss at room temperature. Meanwhile, the capacitance variation ratio of the samples satisfied the EIAX7R temperature characteristic specification.Secondly,K0.5Bi0.5TiO3ceramics withBaNb2O6addition ceramics weresynthesized by a conventional solid state reaction method. The crystal structures,microstructure, dielectric and piezoelectric properties of the ceramics wereinvestigated. The results indicate that an morphotropic phase boundaryseparating rhombohedral and tetragonal phases was identified in the compositionrange of1mol%to2mol%. When the content ofBaNb2O6is3mol%, a smallamount of secondary phase can be detected, and this means that the solidsolubility ofBaNb2O6inK0.5Bi0.5TiO3ceramic has reached the limit. Withthe increasingBaNb2O6content, the dielectric peak near Tmbecomes broader;meanwhile,Tc, Tmand Tcwshifts to lower temperatures and all samples showdistinct characteristics of the diffuse phase transition. When doping content is1mol%, the degree of diffuseness was1.938, suggesting the occurrence of atypical relaxor behavior. A slim loop can be observed for all compositions,particularly for the composition with3mol%, and a small remanent polarizationPrcan be found for all the samples. In the composition of, which is located nearMPB, and in this region, the coexistence of rhombohedral and tetragonalferroelectric phase provides more spontaneous polarization directions, leading tohigher dielectric and piezoelectric activity, So, the poled specimens show peakvalues of d33~96pC/N, kp~17.8%and Qm~150.At last, the semiconductingBaTiO3/K0.5B i0.5T iO3ceramics were preparedby conventional sintering (CS) and microwave sintering (MS) techniques. Theeffects of different sintering method on the phase composition, microstructureand PTC characteristics of the ceramics were investigated. Meanwhile, we alsostudied the effects ofBaNb2O6addition on the dielectric properties of0.9BaTiO30.1K0.5B i0.5T iO3ceramics. The results show that the sintering cycle ofMS was2.5h; it achieved a higher density at a relative lower sinteringtemperature. Meanwhile, the MS samples showed smaller grain size and uniformgrain growth. The Tcof all samples was shifted to higher temperature with theincrease doping concentration by the two sintering technique, and the roomtemperature resistivity declined firstly and then increased. It was found that theroom temperature resistivity of MS samples were lower than CS samples when they had the same doping concentration. This was because the MS processinhibited the generation of Barium vacancy to some extent; however, the rapidcooling rate reduced the concentration of adsorbed oxygen in grain boundarylayer, which made the resistance jump of MS samples slightly lower than the CSsamples. As a whole, the ceramics doped with0.6mol%by MS can obtained anoptimal comprehensive properties: ρRT~82·cm, lg(ρmax/ρmin)~2.53andTc~133.1℃. When theBaNb2O6content increased from1mol%to4mol%, Thevariation ratio of capacitance of all samples are meet the requirements ofEIA X8R (-55℃~+150℃,△C/C25℃≤±15%) temperature specifications. |
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