Liquid phase sintering of 20Bi(Zn₀.₅Ti₀.₅)O₃-80BaTiO₃ dielectrics with bismuth-zinc-borate and bismuth borosilicate glasses

Dielectrics in the Bi(Zn₀.₅Ti₀.₅O₃-BaTiO₃ system (specifically 20BZT-80BT, in mol%) are promising candidates for high energy density capacitor applications due to broad temperature-dependent dielectric constant maxima and a relatively field-independent permittivity. Bulk samples require sintering temperatures of greater than 1180ºC to reach useful densities. Due to incompatibility of Bi with low-pO₂ processing, BZT-BT-based multilayer capacitors must utilize noble metal electrodes that resist oxidation during sintering. Sintering temperatures must be reduced to allow use of less expensive electrode materials (Cu, etc.). This work studies the reduced temperature sintering behavior and dielectric properties of BZT-BT sintered with 30 Bi₂O₃-30ZnO-40B₂O₃ and 50Bi₂O₃-25B₂O₃-25SiO₂ (mol%) liquid phase formers. Dielectrics sintered with 1v% borate additions and 5v% additions of either the borate or borosilicate achieved relative densities ≥95% after sintering at 1000ºC for four hours. All compositions retained the relaxor behavior exhibited by pure 20BZT-80BT. Increased borate additions led to greater dielectric constant reductions, while increased borosilicate additions yielded no clear trend in the dielectric constant reduction. Energy densities were estimated between 0.3-0.5 J/cm³; smaller glass additions typically led to larger energy densities. Dielectrics sintered with 1v% borate additions are of interest due to their high relative densities (≈96%) and energy densities ≈0.5 J/cm³ under 100kV/cm electric fields. Studies of BZT-BT/glass interfaces revealed the formation of crystalline interfacial layers ≤10 µm thick. The borate formed a bismuth titanate phase (likely Bi₄Ti₃O₁₂) during heating to 700ºC, whereas the borosilicate formed a barium silicate phase (likely BaSiO₃) during processing to 800ºC. Similar phases are expected to be present in the liquid phase sintered dielectrics and likely affect the BZT-BT sintering and dielectric behavior --Abstract, page iii