New perovskite materials of the La2−xSrxCoTiO6 series

Abstract

Substitution of La(3+) by Sr(2+) in the double perovskite La(2)CoTiO(6) yields materials of the La(2-x)Sr(x)CoTiO(6) series showing a significant amount of trivalent cobalt ions when prepared at ambient atmosphere. The as-prepared compounds can be reduced in severe conditions retaining the perovskite structure while inducing the formation of a large amount of oxygen vacancies. The limit of aliovalent substitution in this series was found to extend up to x = 1. For substitution of La(3+) up to 15% cobalt and titanium are ordered, though the order is progressively lost as x increases; for x≥ 0.30 no ordering is observed as evidenced by magnetic measurements. The ability of these materials to present either cobalt ions in a mixed oxidation state or large amounts of anion vacancies depending on the atmosphere makes them interesting to be further investigated regarding their electrical and electrochemical properties, and hence, their usefulness in some electrochemical devices.

Characterization of La0.5Sr0.5Co0.5Ti0.5O3−δ as symmetrical electrode material for intermediate-temperature solid-oxide fuel cells

“…However, the crystal structure of the reduced phase, where superstructure reflections were absent, was defined in the Pm-3m space group ( refined occupancy factors of oxygen atoms were refined for the reduced phase, leading to the La 0.5 Sr 0.5 Co 0.5 Ti 0.5 O 2.64 (1) stoichiometry. This result is in disagreement with those reported by Yuste et al [19], who described an orthorhombic Pbnm symmetry for reduced La 0.5 Sr 0.5 Co 0.5 Ti 0.5 O 3Àd from XRD data; the present study from NPD was essential to unveil the true symmetry and space group. Therefore, for both oxidized and reduced phases the Co and Ti atoms are randomly distributed and no crystallographic long-range order was observed.…”

“…Room temperature NPD data corroborate that the oxidized phase can be defined in the orthorhombic Pbnm space group (No. 62), Z ¼ 4, as was previously reported by Yuste et al [19]. La, Sr and O1 atoms are located at 4c (x,y,1/4) positions, Co and Ti distributed at random at 4b (1/2,0,0), and O2 oxygen atoms at 8d (x,y,z) sites.…”

“…The presence of Co 2þ and Co 3þ mixed-valence-cations in perovskite-like cobaltites ((A,A 0 )CoO 3Àd ; A,A 0 : rare earths and/or alkali earths) would allow oxygen-deficient oxides to be obtained under reducing conditions (by reduction of Co 3þ eCo 2þ ), giving rise to the formation of anionic vacancies and oxygen-ion mobility thus promoting oxygen conduction [19].…”

Defect Chemistry, Electrical Properties, and Evaluation of New Oxides Sr2CoNb1−xTixO6−δ (0≤x≤1) as Cathode Materials for Solid Oxide Fuel Cells

“…We have recently studied the La 2− x Sr x CoTiO 6 (0≤ x <1) and La 2− x CoTiO 6− δ (0.05< x <0.20) series. In the former, La/Sr replacement produces a significant increase of electronic conductivity (from 3.6×10 −2 S cm −1 for the parent compound to 1.4 S cm −1 for x= 0.4), in as much as the sole charge‐compensation mechanism is the oxidation of Co 2+ to Co 3+ with the consequent increase of positive charge carriers.…”

Exploring the physical properties of Eu2SrCo1.5Mn0.5O7, a new n = 2 member of the Ruddlesden–Popper series (Eu,Sr)n+1(Co,Mn)nO3n+1

“…[12][13][14] In general, Co-R-P oxides exhibit high catalytic activity for oxygen reduction and high electronic conductivity but relatively high thermal expansion coefficients (TEC), like the Co-perovskites. 22 . Sample purity was determined by powder X-ray diffraction (PXRD) (these data were also used for the structure characterization) on a Bruker D8 high-resolution diffractometer equipped with a LynxEye® fast detector using monochromatic CuK α1 (λ = 1.5406 Å) radiation obtained with a germanium primary monochromator.…”