Sintering behavior and electrical properties of the paraelectric/dielectric composite system BST/MBO

The composite system Ba0.6Sr0.4TiO3/Mg3B2O6 (BST/MBO) was investigated in regard to the influence of sintering temperature and composition on the dielectric properties. Dilatometry measurements were carried out at up to 1200 degrees C. At 1050 degrees C, all composites with an MBO content of 22.0 vol% or more showed densities over 90 % of the theoretical value. An in-situ XRD study was conducted at up to 1200 degrees C. The formation of Mg2TiO4 was detected starting at 1120 degrees C. These data sets were used to make a set of compositions ranging from 17.8-79.7 vol % MBO. At 1050 degrees C, the element distribution at the BST/MBO interfaces was investigated via EDX and ToF-SIMS. It was observed that titanium migrates from the BST into the MBO, mostly in the interface region. The microstructure of the different compositions was determined via SEM and image analysis. Traces of a third phase were found even for samples sintered at 1050 degrees C. The dielectric properties of the samples were measured at 13.56 MHz and compared to the expected behavior from the literature. It was found that compositions in the middle of the spectrum showed reduced permittivity, loss, and tunability, resulting in an overall increase in the material quality factor when compared to the chosen model. This was attributed to the passivation of the BST at the interfaces.