Solid-state reactive sintering mechanism for proton conducting ceramics

The effects of NiO addition on the structure and transport properties of proton conducting BaZr0.8Y0.2O3−

“…Corresponding lattice parameters are a = 4.2115 (3) Å for BZY and a = 3.7289 (6) Å, b = 5.8124 (6) Å, and 11.433 (2) Å for BaY 2 NiO 5 , respectively. The lattice parameters of both phases are in good agreement with the results from solid state reactive sintering [11][12][13]. The ionic radii of Ni 2+ , Zr 4+ , Y 3+ , and O 2À at sixfold coordination are 0.69 Å, 0.72 Å, 0.9 Å, and 1.4 Å, respectively, whereas that of Ba 2+ at 12-fold coordination is 1.61 Å [15].…”

“…The reported sintering time of solid state reactive sintering for BZY with 2 wt.% NiO is over 10 h at 1450°C to obtain 95% relative density [11][12][13]; the preparation of dense BZY from the calcined powder using a conventional solid state reaction is hence an effective means of obtaining dense BZY. SEM micrographs of BZY discs embedded within same BZY powder sintered at 1450°C for 5 h under ambient air and O 2 are shown in Fig.…”

“…More recently, Tong et al [11,12] screened a number of metal oxides to enhance the densification and grain growth of BZY from BaCO 3 , ZrO 2 , and Y 2 O 3 precursors by a solid-state reactive sintering method. Among metal oxide sintering aids, NiO is the most effective one, and the mass percent of the NiO (2 wt.%) has been optimized for the densification of BZY with relative density higher than 95% [13]. It also has been found that a minor secondary phase, BaY 2 NiO 5 , is formed in addition to the BZY during solid state reactive sintering, and it acts as a sintering center without loss of proton conductivity.…”

Additive effect of NiO on electrochemical properties of mixed ion conductor BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_{3−δ}

“…Diffusion of Ni from the anode into BZCYYb electrolyte during this co-sintering process improves the sinterability of BZCYYb, resulting in a dense electrolyte layer without defects such as pinholes and cracks. 19)21) However, Ni diffusion generally has a negative effect for mixed ion conductors, namely, decrease in proton transport number, which leads to lower open-circuit voltage (OCV). Solid solution of Ni into the lattice of mixed ion conductors causes degradation of protonic conductivity due to decrease in proton concentration, resulting in a low proton transport number.…”

Proton Conductivity of Ni, Y Co-Doped BaZrO<sub>3</sub>

“…In order to overcome these problems, it has been recognized that addition of small amount of transition metal (Co, Ni, Cu, Zn, etc.) as a sintering promotion agent is effective on improvement of sinterability [8] [9] [10] [11] [12]. Because Ni is used for the anode electrode material of a fuel cell [13] [14], further consideration is required to obtain the high performance fuel cell using BZ and BZ-Y electrolyte.…”