Study On Fabrication And Properties Of Multilayer Coated BaTiO₃-based Dielectric Ceramics

As with good dielectric, insulation properties and environment friendly features,BaTiO3ceramic are developed to be the most important dielectric material, however,the curie temperature (Tc) of BaTiO3is low, about125oC, and it limits the applicationin XnR ceramics, especially in electronic industry. It is very necessary to investigateand prepare multilayer ceramic capacitors(MLCC) that can work under a widertemperature range and a higher temperature conditions. In view of the above problems,this paper taked the business purchased BaTiO3nano-powder as coated object, thencoated BaTiO3nano-powder for mono-layer or multi-layer by chemical methods.Inthis paper nano-BaTiO3powder was purchased as coated object, then coated BaTiO3for mono-layer or multi-layer by chemical methods. The effects of the layercomponents and the thickness to the microstucture and dielectic propertis werediscussed.Because of excellent temperature stability of xBi(Zn0.5Ti0.5)O3-(1-x)BaTiO3ceramics, this paper carried out the following works: xBZT-(1-x)BT(x=0.05~0.40)ceramics were synthesized by sol-gel method. The phase structure, microstructure anddielectric properties with different BZT contents were investigated. The results showthat, with the contents of BZT increase, the normal ferroelectric ceramics transformedinto relaxation ferroelectic, showing obvious relaxation behavior, at the same time, themaximum relative permittivity ε m decrease, the dielectric peak was depressed andthe dielectric curve became more flat in high temperature section. By comparison,0.3BZT-0.7BT ceramic had the best dielectric properties, so it was chosen as thecoating layer composition in the further experiment.As we know, Nb、Co oxides were usually used to improve the low temperatureend dielectric temperature stability of BaTiO3ceramics, while BZT-BT have goodeffect on the high temperature end. This paper prepared mono-layer coated BaTiO3ceramics with different contents Nb、Co or0.3BZT-0.7BT by wet chemical method,focused on the study of the effects of the shell on the microstructure and dielectricproperties, including the contents and thickness of shell. As a result, producedBT@(0.03Nb-0.01Co) ceramic sample with the optimal properties at1kHz frequency(ε=2486, tanδ=0.95%, ΔC/C25oC≤±15%(-63oC~138oC)), While the optimal properties of BT@0.7(0.3BZT-0.7BT) ceramic at1kHz frequency (ε=3356, tanδ=3.75%,ΔC/C25oC≤±15%(-7~150oC)).In order to improve the low temperature end and the high temperature enddielectric properties of BaTiO3ceramics at the same time, this paper had designed asort of multi-layer coated structure such as [BT@0.7(0.3BZT-0.7BT)] nano powdercoated with different contents of Nb、Co, then successfully obtained the ceramics withdifferent layer thickness by chemical method,[BT@0.7(0.3BZT-0.7BT)]@(xNb-yCo)and x[BT@(0.03Nb-0.01Co)]@y(0.3BZT-0.7BT) were used to sign the ceramics.The microstructure and dielectric property of [BT@0.7(0.3BZT-0.7BT)]@(xNb-yCo)ceramic systems were investigated, optimal properties (ε=1738, tanδ=1.03%, ΔC/C25oC≤±15%(-55~175oC)) were got when x=0.015and y=0.1. For x[BT@(0.03Nb-0.01Co)]@y(0.3BZT-0.7BT) ceramic system, when shell2thickness is small, it mainlyimprove the low temperature end dielectric temperature stabilitiy because the shell1is the primary factor, on the contrary, it mainly improve the high temperature enddielectric temperature stabilitiy.