Local structure around Mn and Co in LaMn_1−xCo_xO_{3 ± δ}: an EXAFS study

Abstract

Detailed investigations of extended x-ray absorption fine structure (EXAFS) associated with the K-edges of Mn and Co have been carried out for LaMn(1-x)Co(x)O(3 ± δ) (0.3≤x≤1) compounds. It is found that the local structure around Mn is different from that around Co. The distortion in MnO(6) octahedra decreases with the increasing Co content whereas CoO(6) octahedra are undistorted over the entire range of x. The Co-O bond length has been found to decrease with the increase in x. Based on the information about the first shell, the structural anomalies observed in these compounds have been discussed. Complementary information obtained from the XRD and EXAFS studies have been used to explain the behaviour of resistivity in these compounds.

Cobalt‐Doped Perovskite‐Type Oxide LaMnO3 as Bifunctional Oxygen Catalysts for Hybrid Lithium–Oxygen Batteries

“…On the other hand, according to as tudy of the structure of LaMn 1Àx Co x O 3Àd (0.3 x 1), MnO 6 and CoO 6 are two types of local structures of LaMn 1Àx Co x O 3Àd .T he distortion of the local structureM nO 6 decreases with increasingc obalt content, whereas CoO 6 is undistortedo ver the entire range of x. [41] For catalytic materials, ad ecrease in the distorted structure is not conducive to catalysis processes. Thus, although doping cobalt can improved the OER properties of LaMnO 3 ,i ta lso has an egative influence on the catalysis processt hrough changing the crystal structure of LaMnO 3 with increasing amount of Co.…”

“…[41] For catalytic materials, ad ecrease in the distorted structure is not conducive to catalysis processes. [41] For catalytic materials, ad ecrease in the distorted structure is not conducive to catalysis processes.…”

“…On the other hand, according to a study of the structure of LaMn 1− x Co x O 3− δ (0.3≤ x ≤1), MnO 6 and CoO 6 are two types of local structures of LaMn 1− x Co x O 3− δ . The distortion of the local structure MnO 6 decreases with increasing cobalt content, whereas CoO 6 is undistorted over the entire range of x . For catalytic materials, a decrease in the distorted structure is not conducive to catalysis processes.…”

Structural and morphological alterations induced by cobalt substitution in LaMnO3 perovskites

“…Previous studies [58][59][60] also reported that LaMn1-xCoxO3 perovskites are between two different crystal structures, but in those cases, the LaMnO3 perovskite has an orthorhombic structure. The different crystal structure obtained for LaMnO3 might be related with the synthesis method because in those works different methods were used as a classical sol-gel method (without EDTA) [58], an autocombustion method [59] and a coprecipitation method [60]. Therefore, the modified sol-gel method used in our work provides more symmetrical structures that could be beneficial for the electroactivity of the perovskite materials.…”

“…perovskites several works used XAS techniques [59,60,62] to study the local valence state of the transition metal and observed that, simultaneously to Co 2+ insertion, part of Mn 3+ (r = 64.5 pm) needs to be converted into Mn 4+ (r = 53 pm) to preserve the electroneutrality of the structure and, accordingly, the bulk (not necessarily the surface) Mn 4+ /Mn 3+ ratio should increase. Since the size of Mn 4+ species is considerable smaller than that of Mn 3+ , the overall result expected is a slight lattice volume contraction at increasing level of cobalt substitution irrespective of the cell structure adopted.…”