Rietveld Refinement and X-ray Absorption Study on the Bonding States of Lanthanum-Based Perovskite-Type Oxides La1−xCexCoO3

Duc-Chau Nguyen,Chia-Seng Chang,Chih-Hao Lee,Aswin Kumar Anbalagan,Chia-Chin Chu

doi:10.3390/cryst12010050

Duc-Chau Nguyen, Chia-Seng Chang + Show 3 more

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https://doi.org/10.3390/cryst12010050

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Abstract

Metal-oxygen bonding of the Ce-doped LaCoO3 system remains largely unexplored despite extensive studies on its magnetic properties. Here, we investigate the structure and local structure of nanoscale La1−xCexCoO3, with x = 0, 0.2, and 0.4, using the Rietveld refinement and synchrotron X-ray absorption techniques, complemented by topological analysis of experimental electron density and electron energy distribution. The Rietveld refinement results show that LaCoO3 subject to Ce addition is best interpretable by a model of cubic symmetry in contrast to the pristine LaCoO3, conventionally described by either a monoclinic model or a rhombohedral model. Ce4+/Co2+ are more evidently compatible dopants than Ce3+ for insertion into the main lattice. X-ray absorption data evidence the partially filled La 5d-band of the pristine LaCoO3 in accordance with the presence of La–O bonds with the shared-type atomic interaction. With increasing x, the increased Ce spectroscopic valence and enhanced La–O ionic bonding are noticeable. Characterization of the local structures around Co species also provides evidence to support the findings of the Rietveld refinement analysis.

Highlights

IntroductionLanthanum transition metal perovskites (of chemical formula LaBO3) have recently attracted tremendous attention due to their pivotal importance from both fundamental and practical points of view
Lanthanum transition metal perovskites have recently attracted tremendous attention due to their pivotal importance from both fundamental and practical points of view
We present an in-depth investigation on the extended X-ray absorption structure (EXAFS) by fitting to data using the models built from the Rietveld refinement results

Summary

Introduction

Lanthanum transition metal perovskites (of chemical formula LaBO3) have recently attracted tremendous attention due to their pivotal importance from both fundamental and practical points of view. The BO6 octahedron lacks an apical O atom and exposes the B site. This active site plays an essential role in facilitating a variety of catalytic reactions in heterogeneous catalysis [1] and electro-catalysis [2]. Lanthanum cobaltite perovskite LaCoO3 (LCO) endows flexibility in regulating the valence distribution of the Co ion by hole doping or electron doping [4]. This perspective has prompted a burgeoning interest in and extensive studies on the tunable electronic structure of LCO. The objective is to scale down the perovskite structures into the nanoscale regime and incorporate rare earth ions with various valences into these structures to enhance their catalytic activity and expand their applications [5]

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