Premium
The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate
Author(s) -
Bock Jonathan A.,
Chan Jason H.,
Tsur Yoed,
TrolierMcKinstry Susan,
Randall Clive A.
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14351
Subject(s) - strontium barium niobate , strontium , barium , materials science , tungsten , tantalate , phase (matter) , electrical resistivity and conductivity , natural bond orbital , thermoelectric effect , conductivity , mineralogy , analytical chemistry (journal) , inorganic chemistry , ferroelectricity , chemistry , metallurgy , density functional theory , thermodynamics , dielectric , optoelectronics , computational chemistry , physics , organic chemistry , chromatography , electrical engineering , engineering
Strontium barium niobate ( SBN ) is a tungsten bronze family ferroelectric which shows promising thermoelectric properties under reducing conditions. It is found here that the enhanced electrical conductivity of oxygen‐deficient SBN correlates with the formation of a NbO 2 secondary phase. The effects of the reducing environment and the NbO 2 phase formation are studied via a detailed defect chemistry analysis. Increasing amounts of the NbO 2 phase are accompanied by an interesting mechanism where the A‐site occupancy of the SBN matrix increases. The resulting donor defects source the large carrier concentrations which cause the enhanced electrical conductivity necessary for thermoelectric performance. In investigation of the phase equilibria, it is found that a solid solution between (Sr 0.6 ,Ba 0.4 )Nb 2 O 6 and (Sr 0.6 ,Ba 0.4 ) 1.2 Nb 2 O 6 exists and that the A‐site filling is found to occur at more modest reduction conditions in Sr‐ and Ba‐rich compositions. Finally, thermogravimetric analysis of the reoxidation process is performed, and the results suggest that the A‐site filling is compensated ionically. Not only do the presented results explain the enhanced electrical conductivity of oxygen‐deficient strontium barium niobate but also modification of the site occupancies by reduction and reoxidation may widen the design space for property modification in tungsten bronze‐structured materials in general.