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High‐Temperature Structural and Electrical Characterization of Reduced Oxygen‐Deficient Ruddlesden–Popper Nickelates
Author(s) -
Kravchenko Ekaterina,
Neagu Alexandra,
Zakharchuk Kiryl,
Grins Jekabs,
Svensson Gunnar,
Pankov Vladimir,
Yaremchenko Aleksey A.
Publication year - 2018
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201800091
Subject(s) - tetragonal crystal system , chemistry , non blocking i/o , orthorhombic crystal system , electrical resistivity and conductivity , crystal structure , oxygen , conductivity , thermogravimetric analysis , analytical chemistry (journal) , crystallography , biochemistry , organic chemistry , chromatography , electrical engineering , engineering , catalysis
High‐temperature characterization of oxygen‐deficient Sr‐rich (La 1– x Sr x ) 2 NiO 4– δ ( x = 0.5–0.8) solid solutions under mildly reducing conditions with p (O 2 ) ≈ 5 × 10 –5 atm was performed by employing structural and thermal analysis, TEM, and electrical conductivity measurements. Oxygen losses from the crystal lattice on reduction were found to result in a reversible transition from the tetragonal ( I 4/ mmm ) to the orthorhombic ( Immm ) structure and shrinkage of the crystal lattice for the compositions with x > 0.5. TEM and thermogravimetric analysis evidenced slow kinetics of the structural transition. The increase in oxygen deficiency under reducing conditions is accompanied by localization of the electronic charge carriers, a drop of the p‐type electronic conductivity, and a transition from metallic‐like to semiconducting behavior. The extent of changes in oxygen nonstoichiometry, unit‐cell dimensions, average Ni oxidation state, electron–hole concentration, and electronic conductivity on reduction is interrelated with the strontium content. The results suggest that the electrical conductivity of (La 1– x Sr x ) 2 NiO 4– δ ceramics depends mainly on the average Ni oxidation state.