The Research Of Non-uniform Barium Strontium Titanate Ceramics

Barium Strontium Titanate (BST) ceramic material, which has excellent dielectric properties of piezoelectric, ferroelectric, pyroelectric,as the basic raw material of modern electronic ceramics and one of the most important modern functional ceramics, is hailed as "the backbone of electronic ceramics", and Its characteristics of high dielectric constant, low dielectric loss, Curie temperature controlled by Ba/Sr, environmental friendly, make it a bright prospect as capacitor, ferroelectric memory, microwave devices, infrared detector, etc. The doping BST ceramics, complex phase BST ceramics and chip BST ceramics have already been studied extensively and deeply, but there are few reports of non-uniform BST ceramics. BST ceramics with stable performance and non-uniform composition will stay ferroelectric phase transition in broad temperature range, which may improve the performance and temperature stability of the device. In this paper, using the ways of dielectric experiments and theoretical analysis, three kinds of non-uniform BST ceramics, the heterogeneous multilayer BST ceramics, surface-diffused BST and graded BST, are studied.Using the traditional solid-state method, adding the liquid-sintering aid SiO2, the heterogeneous multilayer BST ceramics were successfully achieved, the results of the study show that:The double-layer BST ceramics made of ferroelectric materials and nonferrous electrical material retain ferroelectricity; The experiment was successfully prepared the parallel-layers X7R BST ceramics with the dielectric constant as high as6500and the series-layers X7R BST ceramics with the dielectric constant as high as5800at room temperature; In heterogeneous multilayer BST ceramics, there is mutual diffusion between the adjacent heterogeneous layers,the interdiffusion areas remain perovskite structure, and the the molar content of Ba and Sr in the interdiffusion areas are changeable,which can increase the dielectric constant of the heterogeneous materials’ Curie temperature region,making the temperature-stablity of heterogeneous multilayer BST ceramics more stable than it conld be,and the effect will be more and more obvious with the increase of the layer number.The Fe2O3diffusion BST ceramics were prepared by using painted-surface and low temperature reburning way. The results show that:When Fe2O3is not saturated, the iron content of inside BST ceramics will be showing a gradient, and the Fe content of BST ceramic’s surface is higher than the inside which shows an surface build-up iron phenomenon; Fe2O3diffusion can improve the toughness and impact strength of the ceramic BST, especially the edge of the BST ceramic. Fe2O3diffusion can increase the dielectric constant of BST ceramics, and the way of making diffusion ceramics can be developed for an effective method of connection metal materials and ceramic materials.The analog design of gradient BST ceramics were based on the results of multi-layer and diffusion ceramic which having a high dielectric constant, excellent temperature stability of the dielectric constant, and the dielectric constant stability with a wide range of temperature. This kind of ceramic can be achieved a stable dielectric constant with temperature from-250℃to+120℃, providing an idea looking for temperature stable dielectric constant ceramic and new methods for the developing the properties of solution ceramic materials.