Synthesis and characterization of Ba2+ and W6+ co-doped apatite-type lanthanum silicate electrolytes

Huang

Int J Applied Ceramic Tech

et al. 2021

Vanadium doped La 9.33 Si 6−x V x O 26+0.5x (x = 0.5, 1.0, 1.5) (LSVO) electrolyte powder was prepared by combustion method at 600°C for 5-7 min. The powder was sintered at 1500°C for 3 hours to prepare LSVO ceramics. XPS, IR, XRD, and EIS analysis show that V 5+ doping replaces Si 4+ in [SiO 4 ] to form [Si(V)O 4 ] tetrahedron. With the increase in x, the lattice volume increase. When x = 2.0, the LaVO 4 phase was formed, indicating that the limit doping amount of V 5+ replacing Si 4+ is x ≤ 1.5. The conductivity of LSVO increases significantly with the increase in x (x ≤ 1.0), which attributed to the xV 5 + xSi 4 + ⟶xV • Si + 1∕2xOi * ∕ ∕ defect reaction caused by V 5+ doping. The addition of the interstitial oxygen Oi* in 6 3 channels and the increase of lattice volume leads to increased conductivity. When x = 1.0, the highest conductivity is 1.46 × 10 −2 S•cm −1 (800°C). The doping enhancement conductivity mechanism is the Interstitial oxygen defect-Lattice volume composite enhancement mechanism.

Section: Introductionmentioning

confidence: 99%

Preparation of V doped lanthanum silicate electrolyte ceramics by combustion method and study on conductance mechanism

Huang

Int J Applied Ceramic Tech

et al. 2021

“…In general, the ions with larger radii are more likely to be doped at the La site, whereas the ions with smaller radii are more generally doped at the Si site. As reported in the literature, the closer is the radius of the doping ion to the radius of the doped ion, the easier is the doping process 7–16 . Nickel is one of the most promisingly active metals with low cost.…”

Section: Introductionmentioning

confidence: 99%

“…As reported in the literature, the closer is the radius of the doping ion to the radius of the doped ion, the easier is the doping process. [7][8][9][10][11][12][13][14][15][16] Nickel is one of the most promisingly active metals with low cost. As we all know, the radius of Ni 2+ is higher than that of Si 4+ , and the radius of La 3+ is higher than that of Ni 2+ .…”

Section: Introductionmentioning

confidence: 99%

Analysis of the conduction mechanisms of the Ni doped apatite‐type lanthanum silicate electrolyte ceramics synthesized by the combustion method

Huang

Int J Applied Ceramic Tech

et al. 2021

In this study, the nickel doped apatite‐type lanthanum silicate La9.33Si6‐xNixO26‐x (x = 0, .5, 1.0, 1.5, 2.0) (LSNO) electrolyte powders were successfully generated by using the urea nitrate combustion method at 600°C and 6–8 min. The optimal sintering temperature was determined to be 1500°C on the basis of the linear shrinkage, relative density as a function of temperature, and microcosmic analysis. It was observed that Ni2+ successfully replaced Si4+ in [SiO4] to form the [Si(Ni)O4] tetrahedra. LSNO had a typical p63/m apatite structure of high purity. A significant change in the cell volume of the doped samples was observed, and the cell volume increased with the doped nickel content. The conductivity reached the peak value at x = 1.0 (1.21 × 10−3 S·cm−1, 700°C). Nickel doping introduced the oxygen vacancies and expanded the channels for interstitial oxygen conduction. Further, it also directly reduced the amount of interstitial oxygen in the LSO structure. This led to an enhancement in the conductivity of La9.33Si6‐xNixO26‐x, followed by a decrease on increasing the doped nickel content. The conductivity enhancement in the Ni‐doped LSO resulted from the combination of two mechanisms, namely, the oxygen vacancy defect and lattice volume enhancement mechanism.

“…Apatite-type rare-earth silicate (Figure ) was discovered as an oxide-ion conductor by Nakayama et al It has excellent oxide-ion conductivity at intermediate temperatures of less than 700 °C. − Although lanthanum silicate (LSO) undergoes protonation when exposed to water vapor, it can maintain its structural stability, , and thus can be regarded as having better chemical stability in the SOFC operating environment than YSZ. Such properties are advantageous in applications to SOFC and other ion conductor devices.…”

Section: Introductionmentioning

confidence: 99%

First-Principles Analysis of the Oxide-Ion Conduction Mechanism in Si-Deficient Lanthanum Silicate Apatite

et al. 2022

Si-deficient lanthanum silicate apatites (La9.33+0.67x Si6–0.5x O26, LSOs) have attracted attention for their high oxide-ion conductivities. However, the carrier species and the conduction pathways responsible for the oxide-ion conduction are still unclear. In this study, the conduction mechanism of oxide ions in Si-deficient LSO was studied by first-principles calculations. It was found that Si-deficient LSO can include a small amount of excess oxide ions, which are located at the interstitial site along the c axis. The excess oxide ions in Si-deficient LSO can rapidly diffuse along the c axis by the push–pull mechanism with a potential barrier of 0.35 eV, which involves cooperative movements of two neighboring oxide ions, O4 ions, and the excess oxide ions. The potential barrier height was in good agreement with the experimentally reported activation energy. It is shown that a small amount of excess oxygen contributes critically to oxide-ion conduction in Si-deficient LSO, as was also discussed in stoichiometric La9.33Si6O26. These findings indicate the existence of a mechanism whereby a small amount of excess carriers in the ion-conduction pathways can significantly change the energy profiles for ionic conduction and enhance ion conductivity.