We examine electronic and crystal structures of iron-based superconductors LnFeAsO_1−x H _x (Ln = La, Sm) under pressure by means of x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), and x-ray diffraction. In LaFeAsO the pre-edge peak on high-resolution XAS at the Fe-K absorption edge gains in intensity on the application of pressure up to 5.7GPa and it saturates in the higher pressure region. We found integrated-absolute difference values on XES for Ln = La, corresponding to a spin state, decline on the application of pressure, and then it is minimized when the T _c approaches the maximum at around 5GPa. In contrast, such the optimum value was not detected for Ln = Sm. We reveal that the superconductivity is closely related to the lower spin state for Ln = La unlike Sm case. We observed that As height from the Fe basal plane and As–Fe–As angle on the FeAs₄ tetrahedron for Ln = La deviate from the optimum values of the regular tetrahedron in superconducting (SC) phase, which has been widely accepted structural guide to SC thus far. In contrast, the structural parameters were held near the optimum values up to ∼15GPa for Ln = Sm.

我们研究的电子和晶体结构铁基超导体LN FeAsO _{1- X} ħ _X（LN = La，Sm或）由X射线吸收光谱（XAS），X射线发射光谱（XES），和x的装置在压力下-射线衍射。在 LaFeAsO 中，Fe- K吸收边缘的高分辨率 XAS 上的前边缘峰在施加高达 5.7GPa 的压力时强度增加，并且在更高的压力区域饱和。我们发现Ln = La在 XES 上的积分绝对差值，对应于自旋状态，在施加压力时下降，然后当T _c 在 5GPa 左右接近最大值。相反，对于Ln = Sm没有检测到这样的最佳值。我们揭示了超导性与Ln = La的较低自旋态密切相关，与 Sm 情况不同。我们观察到，对于Ln = La ，Fe 基面的 As 高度和 FeAs ₄四面体上的 As-Fe-As 角偏离了超导 (SC) 相中正四面体的最佳值，这已被广泛接受SC到目前为止。相比之下，对于Ln = Sm ，结构参数保持在最佳值附近，最高可达 15GPa 。