Analysis of structural and electronic properties of Pr₂NiO₄through first-principles calculations

Abstract

The structural and electronic properties of bulk Pr(2)NiO(4+δ) (δ = 0 and 0.031) were analyzed using first-principles calculations based on the density functional theory (DFT) for application to electrode materials in solid-oxide fuel cells (SOFCs). Two structures of Pr(2)NiO(4) were analyzed: one in space group I4/mmm associated with the high temperature tetragonal (HTT) structure, and the other in Bmab with the low temperature orthorhombic (LTO) structure. The main difference between the two structures is the pronounced tilting of the nickelate octahedra found in the Bmab structure. Here, we will show that the difference in the electronic properties between the two structures, i.e. half-metallic for the I4/mmm structure and metallic for the Bmab structure, is attributed to the tilting of the nickelate octahedra. Furthermore, we found that the presence of interstitial O atoms at the Pr(2)O(2) bilayers is responsible for the tilting of the octahedra and thus is a dominant factor in the transition from the I4/mmm structure to the Bmab structure. These results would be of great significance to materials design related to the enhancement of O diffusivity in this material.

Structure and reactivity with oxygen of Pr2NiO4+δ: an in situ synchrotron X-ray powder diffraction study

“…2(c)). It is worth noting that tilts around the O eq -Ni-O eq axis are expected due to the high amount of interstitial oxygen: indeed as calculated for iso-structural La 2 NiO 4+δ , 38,39 O int shifts the four neighbouring O ap along the bond of about 0.5 Å (see Fig. 2a, red stick) inducing a substantial tilt of the octahedra.…”

A perspective on low-temperature solid oxide fuel cells

“…Thus, for example in the Ba 1Àx Sr 220,250 Recent first-principles DFT calculations provide a different perspective on how the oxygen vacancy formation energy, mobility, and surface exchange rate vary with perovskite composition. 215,220,241,[250][251][252][253][254][255] One proposed materials descriptor correlating with the high temperature O-reduction rate is the position of the oxygen O-2p-band center measured relative to the Fermi energy. ‡ As shown in Fig.…”

Oxygen transport in Pr nickelates: Elucidation of atomic-scale features

“…[20] (Fig. 4) with antiferromagnetic binding of the magnetic moments of Ni cations (unlike the work by Aspera et al [34]).…”

“…E.g., according to DFT calculations for La 2−x Sr x NiO 4+δ , migration barrier for this mechanism varies in the range of 0.5-3 eV depending on Ni cations charge compared to 0.3-0.7 eV for cooperative mechanism (the values are close and even value for oxide-peroxide mechanism is slightly lower for Ni cations charge of 2.5+) [36]. Moreover, there is a certain anisotropy in the oxygen transport: oxygen anions diffusion in a-b plane is faster than along the c axis, significant difference in calculated values of both diffusion coefficient and its effective activation energy being reported [23,[25][26][27][31][32][33][34][43][44][45][46][47][48][49]. For undoped Ln 2 NiO 4+δ , it was demonstrated that octahedral rotations in the structure affect the interstitial oxygen transport in I4/mmm structure with the force constant of these rotations becoming "softer" with decreasing the Ln cation radius (with a minimum for Ln = Gd) [23].…”

“…Oxygen transport mechanism in first homologues of R-P phases was modeled by such methods as molecular dynamics (MD) [25][26][27][28][29][30][31][32] and density functional theory (DFT) calculations [23,30,[32][33][34][35][36][37][38][39][40]. The dominating mechanism of oxygen transport in K 2 NiF 4 -like compounds is socalled cooperative mechanism (being also referred to as interstitialcy mechanism [30], cooperative interstitialcy mechanism [31] or interstitialcy-mediated mechanism [36]) as mentioned above involving lattice oxygen of perovskite layers and highly mobile interstitial oxygen of rock salt layers with the second one being able to be accumulated in a large amount [23,30,31,36,38,39,41,42].…”