Abstract
Barium strontium titanate powders with different Ba:Sr ratios were investigated to determine the influence of the initial composition of powder mixture on microstructural properties and sintering kinetics. It was determined that BaCO3 and SrCO3 react differently to mixing, resulting in Ba0.5Sr0.5CO3 in the sample with 80% Ba and different contents of Ba1- xSrxTiO3 in samples with 50% and 20% Ba. In addition, the morphology is also different, with higher Sr content leading to larger particles size and less agglomeration. The different chemical content of the initial powder mixture also has a marked impact on the sintering process: the onset of sintering shifts towards higher temperature with higher Sr content, while the average apparent activation energy of sintering is the highest for the sample with 80% Ba and the lowest for the mixture with 50% Ba. In addition, hexagonal-to-cubic phase transformation was observed in parallel with the sintering process, where the position of the phase transition shifts to lower temperatures with an increase in Sr content. This is consistent with the behavior of low-temperature phase transitions of BST. The phase transition was not observed in sintered samples, suggesting that there is a size-dependence of the phase transition temperature.
Highlights
Barium strontium titanate (Ba,Sr)TiO3 (BST), a typical ferroelectric material with a tetragonal structure, belongs to the family of (ABO3) perovskites, composed of titanate, barium titanate (BaTiO3) and strontium titanate (SrTiO3) [1,2,3,4,5].Pure barium titanate ceramic undergoes a para-ferroelectric phase transition at 120 oC from cubic to tetragonal phase, while the strontium titanate, which has para-ferroelectric phase transition at 163 oC, is usually added into barium titanate in order to lower the Curie point (Tc) and to increase the room temperature dielectric constant of the material [6]
Barium strontium titanate powders with different Ba:Sr ratios were investigated to determine the influence of the initial composition of powder mixture on microstructural properties and sintering kinetics
barium strontium titanate (BST) ceramics are considered good candidates for applications in phased array antennas [10], as well as in capacitors, sensors and PTC thermistors [1113].Properties of BST ceramic are strongly dependent on the stoichiometry, homogeneity, particle size and phase purity of the BST powder [14,15,16], which in turn depends on the synthesis method used [17,18,19,20].The stoichiometry and structural characteristics, including the concentration of oxygen vacancies, of BST powder, is strongly influenced by the initial Ba/Sr ratio in precursor solution relative to Ti, as well as the type of precursor used in the reaction [21]
Summary
Barium strontium titanate (Ba,Sr)TiO3 (BST), a typical ferroelectric material with a tetragonal structure, belongs to the family of (ABO3) perovskites, composed of titanate, barium titanate (BaTiO3) and strontium titanate (SrTiO3) [1,2,3,4,5].Pure barium titanate ceramic undergoes a para-ferroelectric phase transition at 120 oC from cubic to tetragonal phase, while the strontium titanate, which has para-ferroelectric phase transition at 163 oC, is usually added into barium titanate in order to lower the Curie point (Tc) and to increase the room temperature dielectric constant of the material [6]. BST ferroelectrics exhibit high dielectric permittivity and have been widely investigated both in films and ceramics. BST thin films are promising materials for high-density dynamic random-access. BST ceramics are considered good candidates for applications in phased array antennas [10], as well as in capacitors, sensors and PTC thermistors [1113].Properties of BST ceramic are strongly dependent on the stoichiometry, homogeneity, particle size and phase purity of the BST powder [14,15,16], which in turn depends on the synthesis method used [17,18,19,20].The stoichiometry and structural characteristics, including the concentration of oxygen vacancies, of BST powder, is strongly influenced by the initial Ba/Sr ratio in precursor solution relative to Ti, as well as the type of precursor used in the reaction [21]
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