Interactions between bismuth oxide and ceramic substrates for thick film technology

We investigated the interactions between screen printed and fired layers of Bi₂O₃ and ceramic substrates of alumina and beryllia. It was found that the reaction products are invariably crystalline in nature. Several transitions of Bi₂O₃ in its polymorphic phases were found to occur on BeO substrates, while newly formed compounds have been observed to grow on alumina substrates, i.e., Al₄Bi₂O₉ on 99.9% Al₂O₃ and Bi₁₂SiO₂₀ on 96% Al₂O₃. Bismuth deeply penetrates in the ceramic interstices in all the cases. Until Bi₂O₃ is not completely reacted, this penetration is diffusion limited (penetration depth , where t_d is the reaction time) with values of the activation energy ranging from 3.7 ± 0.6 eV (BeO substrate) to 1.4 ± 0.06 eV (96% Al₂O₃ substrate). It is shown that these processes are notably different to those occurring in PbO/ceramic systems; moreover, they imply different adhesion phenomena of thick films on different substrates.