Structural effects of the spin-state crossover at high temperature in the distorted ErCoO3 cobaltite

Jessica Padilla-Pantoja,J A Alonso,José Luis García-Muñoz,M T Fernandez-Díaz

doi:10.1088/1742-6596/663/1/012005

Jessica Padilla-Pantoja, J A Alonso + Show 2 more

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https://doi.org/10.1088/1742-6596/663/1/012005

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Abstract

We present a neutron powder diffraction study reporting structural evidences of a spin- state crossover beginning at Tss≈575 K in the highly distorted ErCoO3 cobaltite, based on measurements in the temperature range 100 K - 1000 K. Different interrelated changes in the structural evolution upon heating have been described, which are driven by an anomalous expansion of the octahedra. The activation of IS or HS spin states brings about an expansion of the CoO6 octahedra (increase of Co-O bond lengths), and the augmentation of the Co-O distances in the a-b plane respect to that along the c-axis. The spin-state crossover extends over a broad temperature interval and can be monitored by an atypical augmentation of the orthorhombic strain.

Highlights

The spin-state nature across the two electronic transitions in LaCoO3 has been matter of controversy for many years [1,2,3,4,5,6,7,8]
The details of the structural model obtained from the refinement at this temperature are reported in Table I, together with the agreement factors
We have observed one shoulder or clear maxima in the thermal evolution of the linear expansion coefficient resulting from the activation of a broad spin-state crossover from LS to intermediate spin (IS) or high spin (HS) states that begins at TSS≈575 K in this highly distorted cobaltite

Summary

Introduction

The spin-state nature across the two electronic transitions in LaCoO3 has been matter of controversy for many years [1,2,3,4,5,6,7,8]. LaCoO3 exhibits two broad transitions: there is first a spin-state crossover (SSC) at TSS (between ~50-100 K), where a hump in the magnetic susceptibility signals the appearance of a paramagnetic semiconductor. For large splitting all the electrons occupy the low energy t2g-levels resulting in zero spin and orbital momentum (low spin state, LS). States with finite spin momentum arise from the transfer of one or two electrons into the higher energy eg-orbitals and correspond to an intermediate spin (IS) or high spin (HS) state, respectively. In presence of disorder phenomena, a LS→HS crossover at TSS can not be totally ruled out [2,7]

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