Synthesis and electrical characterization of Ba5Nb4O15 and Ba5Nb3.9M0.1O(15-δ) (M = Ti, Zr) hexagonal perovskites

• Published in: Ceramics international 2019-03, Vol.45 (4), p.5087-5092
• Main Authors: Kultz. Unti, Luiz Fernando, Grzebielucka, Edson Cezar, Antonio Chinelatto, Adriana Scoton, Mather, Glenn Christopher, Chinelatto, Adilson Luiz
• Format: Article
• Language: English
• Subjects: Barium niobate; Hexagonal perovskites; Pechini method; Protonic conduction
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/j.ceramint.2018.11.211

The 5H-type hexagonal perovskite Ba5Nb4O15 was synthesized by solid-state reaction and the Pechini method and acceptor-doped phases Ba5Nb3.9M0.1O15-δ (M = Ti, Zr) by the former route. Monophasic doped and undoped material was obtained on final sintering at 1450 °C for 4 h with the M-doped samples leading to a reduced c-parameter. Scanning electron microscopy revealed a morphology of interlacing elongated plaques for all compositions, but with reduced grain size for the doped compositions. The highest density (95.1%) was observed for the Pechini-synthesized phase, whereas Zr doping had a deleterious effect on densification. The electrical transport properties were measured in H2O- and D2O-humidified air in the temperature range 300–550 °C by impedance spectroscopy. The presence of a H+/D+ isotope effect confirms the presence of proton conductivity in this structure type. Ba5Nb4O15 synthesized by the Pechini method exhibits a conductivity of 8.4 × 10−6 S.cm−1 at 550 °C in humidified air with an activation energy of 0.75 eV. The M-doped samples presented lower total conductivities, most probably due to the larger grain-boundary volume associated with their smaller grain size.