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首页> 外文期刊>Physical review >Pressure dependence of the low-temperature crystal structure and phase transition behavior of CaFeAsF and SrFeAsF: A synchrotron x-ray diffraction study
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Pressure dependence of the low-temperature crystal structure and phase transition behavior of CaFeAsF and SrFeAsF: A synchrotron x-ray diffraction study

机译：CaFeAsF和SrFeAsF的低温晶体结构的压力依赖性和相变行为：同步加速器X射线衍射研究

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摘要

We report systematic investigation of high pressure crystal structures and structural phase transition up to 46 GPa in CaFeAsF and 40 GPa in SrFeAsF at 40 K using powder synchrotron x-ray diffraction experiments and Rietveld analysis of the diffraction data. We find that CaFeAsF undergoes orthorhombic to monoclinic phase transition at P_c=13.7 GPa while increasing pressure. SrFeAsF exhibits coexistence of orthorhombic and monoclinic phases over a large pressure range from 9 to 39 GPa. The coexistence of the two phases indicates that the transition is of first order in nature. Unlike in the 122 compounds (BaFe_2As_2 and CaFe_2As_2), we do not find any collapse tetragonal transition. The transition to a lower symmetry phase (orthorhombic to monoclinic) in 1111 compounds under pressure is in contrast with the transition to a high symmetry phase (orthorhombic to tetragonal) in 122-type compounds. On heating from 40 K at high pressure, CaFeAsF undergoes monoclinic to tetragonal phase transition around 25 GPa and 200 K. Further, it does not show any post-tetragonal phase transition and remains in the tetragonal phase up to 25 GPa at 300 K. The d P_c/dT is found to be positive for the CaFeAsF and CaFe_2As_2, however the same was not found in case of BaFe_2As_2.
机译：我们报告了使用粉末同步加速器X射线衍射实验和Rietveld分析衍射数据对CaFeAsF中高达46 GPa和SrFeAsF中40 GPa的高压晶体结构和结构相变的系统研究。我们发现，CaFeAsF在压力增加的同时，在P_c = 13.7 GPa时经历了正交晶向单斜相的转变。在9至39 GPa的较大压力范围内，SrFeAsF表现出正交相和单斜相的共存。这两个阶段的共存表明过渡实际上是一阶的。与122种化合物（BaFe_2As_2和CaFe_2As_2）不同，我们没有发现任何塌陷的四方过渡。在压力下，1111种化合物向低对称相的转变（斜方向单斜晶）与122型化合物向高对称相的转变（斜方向四方晶）相反。在高压下从40 K加热时，CaFeAsF在25 GPa和200 K附近经历单斜晶相向四方相的转变。此外，CaFeAsF在300 K时不显示任何四方相后的转变，并保持高达25 GPa的四方相。 d P_c / dT被发现对于CaFeAsF和CaFe_2As_2为正，但是在BaFe_2As_2情况下却没有。

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  • 来源
    《Physical review》 |2011年第22期|p.224513.1-224513.12|共12页
  • 作者

    S. K. Mishra; R. Mittal; S. L. Chaplot; S. V. Ovsyannikov; D. M. Trots; L. Dubrovinsky; Y. Su; Th. Brueckel; S. Matsuishi; H. Hosono; G. Garbarino;

  • 作者单位

    Solid State Physics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India;

    Solid State Physics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India;

    Solid State Physics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India;

    Bayerisches Geoinstitut, Universitat Bayreuth, Universitatsstrasse 30, D-95440 Bayreuth, Germany;

    Bayerisches Geoinstitut, Universitat Bayreuth, Universitatsstrasse 30, D-95440 Bayreuth, Germany;

    Bayerisches Geoinstitut, Universitat Bayreuth, Universitatsstrasse 30, D-95440 Bayreuth, Germany;

    Juelich Centre for Neutron Science, IFF, Forschung. Juelich, FRMII, Lichtenbergstr. I, D-85747 Garching, Germany;

    Juelich Centre for Neutron Science, IFF, Forschung. Juelich, FRMII, Lichtenbergstr. I, D-85747 Garching, Germany,Institutfuer Festkoerperforschung, Forschungszentrum Juelich, D-52425 Juelich, Germany;

    Frontier Research Center, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku,Yokohama 226-8503, Japan;

    Frontier Research Center, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku,Yokohama 226-8503, Japan;

    European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France;

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  • 正文语种 eng
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  • 关键词

    superconducting materials; crystallographic aspects of phase transformations; pressure effects; transition-metal compounds;

    机译：超导材料;相变的晶体学方面;压力影响;过渡金属化合物;

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