Dielectric properties of tape cast Ba0.65Sr0.35TiO3 derived from sol-gel for application in multilayered capacitors

The tape casting technique using a doctor-blade is used to fabricate thin dielectric sheets of barium strontium fitanate (Ba1-xSrxTiO3) with x = 0.35 (abbreviated as BST). Initially, fine powder of Ba0.65Sr0.35TiO3 is prepared by the sol-gel method. Two kinds of tape are used for the stacks, i.e.parallel to (the direction of the layer is alone, the tape direction (in the casting direction)) and perpendicular to (the direction of the layer is perpendicular to the tape direction (across the tape)). Further, two stacking sequences are used for stacking layers of tape, i.e. (the layers are in stacks in which all the layers are parallel to, abbreviated as the parallel tosequence) and parallel to-perpendicular to-parallel to- (the layers are in stacks such that every other layer is perpendicular to the casting direction, abbreviated as the perpendicular to sequence). Therefore, in the latter stacking sequence the top and bottom layers are always parallel to the casting direction and each perpendicular to layer is sandwiched between two parallel to layers. It has been observed that the green density remains unaffected by any change of sequence. However, the density of fired tape cast BST changes significantly with change of sequence. For example.. the density of multilayered BST with eleven layers is enhanced from approximate to3.5 cm(-3) to approximate to4 g cm(-3) when the sequence changes from parallel to and perpendicular to. Observations of the microstructure of multilayered BST under the scanning electron microscope suggest that the packings of particles and pores are strongly dependent on the sequence. The dielectric permittivity of sintered tape cast BST is found to increase with increasing number of layers and temperature; however, it is higher for the perpendicular to sequence. A comparison has also been made of the dielectric properties of tape cast BST derived from powders obtained from sol-gel and by conventional methods. Investigations on BST are highly desirable in relation to applications in multilayered capacitors in the electronics and communications industries.