Synthesis of doped Ba0.6Sr0.4TiO3 ceramic powder via a sol–freeze-granulation and freeze-drying process

This paper presents a method for synthesizing undoped and doped ceramic (Ba,Sr)TiO3(BST) powders. The method is based on a sol-drying process utilizing freeze-granulation and freeze-drying of freshly prepared sols. The presented route is flexible regarding the stoichiometry of the powders and the chemistry of the utilized doping agent. Starting materials are the alkaline-earth acetates and titanium isopropoxide. The used solvent is a mixture of glacial acetic acid and water. The resulting precursor powder exhibits spherical and highly porous granules. The microstructure of the granules shows cell-like structures with wall thicknesses in the range of 100 nm or less. The primary particle size can be varied between 40 nm and several hundred nm by simply varying the calcination temperature. At higher calcination temperatures the agglomerates are easier to destroy by ultrasonic treatment. The tested dopants were Fe3+, Ta5+ and Fe3++F−Fe3++F−. The differently doped precursor and ceramic powders were examined using SEM-, TEM-, BET-, XRD- (with Rietveld-refinement), laser diffraction- and X-ray-fluorescence-techniques.This method is well suited to provide variably and homogeniously doped precursors for the preparation of ceramic powders in the system BaO–SrO–TiO2, which allows even the incorporation of fluoride anions and can be easily deagglomerated. Moreover codoping BST with Fe3+ and F− has a significant impact on lattice spacings of the resulting ceramic powders.