Mixed ionic-electronic conductivity features of A-site deficient Nd nickelates

Intolerance of the Ruddlesden–Popper La2NiO4+δ Structure to A-Site Cation Deficiency

“…As shown in the present work, ceramics with nominal composition Nd 1.95 NiO 4+δ sintered at 1450 °C comprises segregated nickel oxide. The presence of NiO secondary phase is evident in XRD patterns of Nd 1.95 NiO 4+δ and (Nd 2– x Ca x ) 0.975 NiO 4+δ ( x = 0.1–0.5) reported in ref . Segregation of NiO in Nd 1.9 Ni 0.75 Cu 0.25 O 4±δ samples was revealed by SEM/EDS analysis and supported by XRD data .…”

“…Similar inconsistencies can be found in available literature reports on A-site-deficient nickelates derived from Nd 2 NiO 4+δ – and Pr 2 NiO 4+δ . – The following communications are worth highlighting, among others, in the context of the present work. Boehm et al claimed the formation of phase-pure Nd 2– x NiO 4+δ ( x = 0–0.10) nickelates with an orthorhombic K 2 NiF 4 -type structure.…”

Design of Mixed Ionic-Electronic Materials for Permselective Membranes and Solid Oxide Fuel Cells Based on Their Oxygen and Hydrogen Mobility

“…The important feature of RP phases, which makes them attractive SOFC cathodes and oxygen-separation-membrane materials, is a fine oxygen transport provided via the cooperative mechanism of oxygen migration. In this case, both lattice and interstitial oxide anions accumulating at a high level are involved in the process of oxygen transport ( Figure 20 ) [ 55 , 58 , 60 , 63 , 69 , 159 , 285 , 288 , 291 , 292 , 293 , 294 , 295 , 296 , 297 ]. This allows them to reach superior oxygen mobility compared to other MIECs ( Figure 21 ).…”

“…This allows them to reach superior oxygen mobility compared to other MIECs ( Figure 21 ). On the other hand, doping with alkaline earth metals (Ca, Sr, Ba), which significantly improves total conductivity, leads to an apparent decrease in the oxygen tracer diffusion coefficient values due to a decrease in the interstitial oxygen content and a larger size of dopant cations resulting in steric hindrances for the oxygen transport [ 287 , 288 , 292 , 298 , 299 , 300 ]. In some cases, it leads to the formation of slow diffusion channels with complicated pathways ( Figure 21 ).…”

“…With a decreasing host Ln cation size in the row of Ln = La, Pr, Nd, this effect becomes less pronounced. Introducing A-site deficiency can slightly increase oxygen diffusivity [ 55 , 69 , 292 , 301 , 302 , 303 ]. Doping La 2 NiO 4+δ with other lanthanides (Nd, Sm, Gd, Eu, etc.)…”