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Manifold of spin states and dynamical temperature effects in LaCoO_3 Experimental and theoretical insights

机译：LaCoO_3中的自旋流形和动态温度效应实验和理论见解

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The unconventional transport and magnetic properties of perovskitelike lanthanum cobalt oxide LaCoO3 have been studied for more than five decades. This highly correlated electron system exhibits a variety of peculiar properties that are desirable for environmentally friendly energy solutions, fuel cell technologies, novel diesel engines, and oxyfuel power plants. However, the true spin state of the Co3+ ion is an important but still unresolved issue that underlies these applications. Although many theoretical models have been proposed, finding supporting experimental evidence of spin-state transitions is extremely difficult. Not until recently have new advanced scattering methods emerged allowing unprecedented precision in determining the crystal structure of LaCoO3. In this work, we combine high-resolution extended x-ray absorption fine structure, x-ray powder diffraction, and neutron powder and single-crystal diffraction over a broad range of temperatures, from 2 up to 1000 K, as well as quantum mechanical modeling to study the spin-state transition in LaCoO3 and in a reference sample of LaGaO3. Our results suggest that the Co ions are mainly in a low-spin state at temperatures below 150 K, with a minority of ions in a high-spin state. With an increase in the temperature the gradual transition from low- to intermediate-spin state occurs up until 550 K. At the metal-insulator transition at 550 K, the long-range domains of the intermediate-spin states become a dominant contribution. Above 550 K, a transition from intermediate- to high-spin state is observed. It is established that a slight change in the degree of pd hybridization can lead to the appearance of a spin-state transition which might be induced by both temperature and surface effects in powder crystallites.
机译：钙钛矿状镧钴酸镧LaCoO3的非常规输运和磁性已经研究了五十年以上。这种高度相关的电子系统展现出各种独特的特性，这些特性对于环境友好型能源解决方案，燃料电池技术，新型柴油发动机和富氧燃料电厂而言是理想的。但是，Co3 +离子的真实自旋态是重要的但仍未解决的问题，是这些应用的基础。尽管已经提出了许多理论模型，但是找到自旋态转变的支持性实验证据极其困难。直到最近，才出现了新的高级散射方法，该方法允许在确定LaCoO3的晶体结构方面实现前所未有的精度。在这项工作中，我们将高分辨率扩展的X射线吸收精细结构，X射线粉末衍射以及中子粉末和单晶衍射结合在2至1000 K的宽温度范围内，以及量子力学建模以研究LaCoO3和LaGaO3的参考样品中的自旋态跃迁。我们的结果表明，Co离子在低于150 K的温度下主要处于低旋态，而少数离子处于高旋态。随着温度的升高，直到550 K为止，从低自旋态逐渐过渡到中间自旋态。在550 K的金属-绝缘体转变中，中间自旋态的长程域成为主要贡献。高于550 K时，观察到从中间旋转到高旋转状态的转变。可以确定的是，pd杂交程度的轻微变化会导致出现自旋态转变，这可能是由粉末微晶的温度和表面效应共同引起的。

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  • 来源
    《Physical review》 |2019年第5期|054306.1-054306.10|共10页
  • 作者

    Feygenson M.; Novoselov D.; Pascarelli S.; Chernikov R.; Zaharko O.; Porcher F.; Karpinsky D.; Nikitin A.; Prabhakaran D.; Sazonov A.; Sikolenko V;

  • 作者单位

    Forschungszentrum Julich JCNS 1 D-52425 Julich Germany;

    Russian Acad Sci Ural Branch MN Mikheev Inst Met Phys 18 S Kovalevskaya St Ekaterinburg 620108 Russia|Ural Fed Univ 19 Mira St Ekaterinburg 620002 Russia;

    European Synchrotron Radiat Facil BP 220 F-38043 Grenoble France;

    Canadian Light Source 44 Innovat Blvd Saskatoon SK S7N 2V3 Canada;

    Paul Scherrer Inst Lab Neutron Scattering & Imaging CH-5232 Villigen Switzerland;

    CEA Saclay Lab Leon Brillouin F-91191 Gif Sur Yvette France;

    NAS Belarus Sci Pract Mat Res Ctr Minsk 220072 BELARUS;

    Clarendon Lab Parks Rd Oxford OX1 3PU England;

    DMSC ESS ERIC DK-2200 Copenhagen Denmark;

    Joint Inst Nucl Res Joliot Curie 6 Dubna 141980 Russia;

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