Tailoring the properties of dense yttrium‐doped barium zirconate ceramics with nickel oxide additives by manipulation of the sintering profile. (16th July 2022)

• Record Type: Journal Article
• Authors: Shakel, Zinaida; Loureiro, Francisco J. A.; Antunes, Isabel; Mikhalev, Sergey M.; Fagg, Duncan P.
• Is Part Of: International journal of energy research. Volume 46:Number 15(2022)
• Page Start: 21989
• Page End: 22000
• Publication Date: 2022-07-16
• Subjects: electrochemical impedance spectroscopy -- liquid phase sintering -- NiO sintering additive -- protonic conductivity -- two‐step sintering -- yttrium‐doped barium zirconate; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Power resources -- Research -- Periodicals; 621.042
• DOI: 10.1002/er.8389
• Languages: English
• ISSNs: 0363-907X

Abstract

Summary: Liquid phase sintering (LPS), by the addition of transition metal additives, has become one of the most preferred approaches to lower the sintering temperature of yttrium‐doped barium zirconate (BZY) proton‐conducting ceramics. Nonetheless, this approach is known to negatively impact the bulk conductivity of the parent perovskite phase, due to the significant incorporation of the sintering additive into the bulk composition. In the current work, we study the typical proton conducting material BaZr0.8 Y0.2 O3−δ (BZY20), prepared by One or Two‐step sintering strategies using 4 mol% NiO of sintering additive, compared against a control sample of pure BZY20. The main results demonstrate that the Two‐step approach is shown to minimise Ni interreaction with the BZY material, allowing this sample to maintain a higher hydration capacity than the One‐step material, as confirmed by X‐ray diffraction (XRD), scanning transmission electron microscopy/energy‐dispersive spectrocopy (STEM/EDS) and thermogravimetric (TG) measurements. Despite these benefits, the Two‐step approach presents a diminished bulk conductivity, which was ascribed to depletions in proton mobility due to " proton trapping " effects. In addition, the specific grain boundary conductivity was revealed to be higher in the Two‐step sample, as a possible result of a higher Ni accumulation in this region. Overall, this work opens an exciting new debate for further studies, in that prevention of Ni‐incorporation in the bulk material, as typically suggested in current literature, may not actually be the best method to improve the conductivity of samples densified by Ni‐additives and that control of potential defect associations may be the more critical method for conductivity tailoring. Abstract : Although doped barium zirconate (BZY) has emerged as one of the best ceramic proton conductors its poor densification requires the use of sintering additives. Such additives, however, commonly deplete its bulk conductivity due to their accommodation into the bulk composition. In this work, we attempt to manipulate Ni sintering additive incorporation by modification of sintering profile. The impact of One‐step and Two‐step sintering on Ni‐incorporation and, thus, on subsequent levels of bulk, specific grain boundary conductivity and hydration are discussed.