Preparation and Performance of BSCF-based Mixed Ionic-Electronic Conducting (MIEC) Ceramics

Abstract

Preparation and performance of the perovskite-type barium strontium cobalt iron oxide (Ba_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_(3-delta), BSCF) and its doped compositions were studied in this dissertation.Three transition metals (copper, nickel and niobium) were substituted into the parent BSCF at various ratios to create the formula Ba_0.5 Sr_0.5 (Co_0.8 Fe_0.2)_(1-x) M_x O_(3-delta) (0.02smaller or equal toxsmaller or equal to0.30; M=Cu,Ni or Nb). Two synthetic methods (solid-state reaction and wet chemical co-precipitation) were developed for the preparation of starting powders. In the previous reports [1, 2], BSCF ceramics suffered from insufficient densification and severe cracking; these problems were resolved in this study by optimising the ceramic processing conditions.The phase transition sequences from starting powders to single-phase cubic perovskite were studied by SEM, XRD, TGA, EDS and Raman spectroscopy. The powders prepared by solid-state method were found to require higher calcination temperature to form pure perovskite phase, and an extra intermediate structure (Ba,Sr)Fe_2 O_4 was detected in the reaction sequence.The materials performance was examined from five aspects: thermal stability, chemical stability, oxygen permeability, electronic conductivity and mechanical performance. The secondary phases of thermal/chemical degradation were investigated, and a needle-like intragranular precipitate was originally discovered in this work. It was discovered that the niobium substitution could significantly improve BSCF's thermal stability and chemical stability. The oxygen permeability and mechanical performance were also improved by niobium when the substitution ratios are small (

Date of Award	1 Aug 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Colin Leach (Supervisor)