Chemical and structural changes in Ln2NiO4 (Ln=La, Pr or Nd) lanthanide nickelates as a function of oxygen partial pressure at high temperature

La2NiO4+δ infiltrated into gadolinium doped ceria as novel solid oxide fuel cell cathodes: Electrochemical performance and impedance modelling

“…It is determined by means of TGA measurements [34], and corresponds to f ¼ À1=2$vlnðp O2 Þ=vlnðdÞ, d being the oxygen overstoichiometry of La 2 NiO 4þd . V m is the molar volume of LNO determined by X-ray diffraction vs. temperature [34]. Finally, S A is the specific surface area of the electrode measured as stated above.…”

Structural transformations of the La2−xPrxNiO4+δ system probed by high-resolution synchrotron and neutron powder diffraction

“…29,30 More recent structural studies of non-stoichiometric La2NiO4+δ compositions have focused on low temperature orthorhombic (LTO) and high temperature tetragonal (HTT) structures under variable oxygen partial pressures, reflecting a shift of research focus on these materials from superconductivity towards the mixed ionicelectronic conductivity properties of layered rare earth nickelates. [31][32][33] Despite early initial conjecture of a monoclinic structural distortion for Pr2NiO4+δ, 20,34,35 most subsequent studies reported orthorhombic or tetragonal structures depending on temperature and oxygen δ content. 10,36-41 Sullivan et al examined a wide range of non-stoichiometric Pr2NiO4+δ oxygen values (0 ≤ δ < 0.22) and proposed a phase diagram with multiple single and mixed-phase regions distinguished by different canting arrangements of NiO6 octahedra.…”

Impact of Oxygen Deficiency on the Electrochemical Performance of K2NiF4‐Type (La1−xSrx)2NiO4−δ Oxygen Electrodes

“…At ambient temperature, the symmetry of the La 2 NiO 4+ δ crystal lattice depends on the level of frozen‐in oxygen overstoichiometry δ . Above ∼450 °C, the equilibrium oxygen excess decreases on heating and on reducing the oxygen partial pressure, and the tetragonal structure (space group I 4/ mmm ) is retained over the entire oxygen nonstoichiometry range …”

“…Lanthanum nickelate La 2 NiO 4+ +d with ap erovskite-related K 2 NiF 4 -type structure possessesacomparatively high electronic conductivity, [1][2][3][4][5] high oxygen diffusivity and surface exchange kinetics, [4][5][6][7][8][9][10] and moderate thermal and low chemical expansion, [3,5,[11][12][13] and is, therefore, considered as ap romising mixed ionic-electronic conductor (MIEC) for high-temperature electrochemical applications, such as dense MIEC membranes for oxygen separation [4,14,15] and oxygen electrodes for solid oxide fuel/electrolysis cells (SOFC/SOEC). [3,9,[16][17][18][19][20] Good electronic transport Scm À1 at 800 8Ci na ir) [1][2][3][4][5]21] is provided by the mixed 2+ +/3+ + oxidation state of the Ni cations in the perovskite layers of the Ruddlesden-Popper K 2 NiF 4 -type structure whereas ionic transport in La 2 NiO 4+ +d occurs predominantly through the migration of interstitial oxygen in rock-salt-type LaO layers.…”

“…[22][23][24][25][26] At ambient temperature, the symmetry of the La 2 NiO 4+ +d crystal lattice depends on the level of frozen-in oxygen overstoichiometry d. [27][28][29] Above~450 8C, the equilibrium oxygen excess decreases on heating and on reducingt he oxygen partial pressure, and the tetragonal structure (space group I4/mmm)i sr etained over the entireo xygen nonstoichiometry range. [11][12][13]28] The oxygen nonstoichiometry and transport properties of La 2 NiO 4+ +d can be alteredb ys ubstitutions in both the Aa nd B sublattices. (La 1Àx Sr x ) 2 NiO 4 AE d is probablyt he most studied system based on K 2 NiF 4 -type lanthanum nickelate.…”