National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan.
Max Planck Institute for Chemical Physics of Solids, Dresden, D-01187, Germany.
Sci Rep. 2017 Jun 16;7(1):3656. doi: 10.1038/s41598-017-03950-z.
The pressure-response of the Co-O bond lengths and the spin state of Co ions in a hybrid 3d-5d solid-state oxide SrCoIrO with a layered KNiF-type structure was studied by using hard X-ray absorption and emission spectroscopies. The Co-K and the Ir-L X-ray absorption spectra demonstrate that the Ir and the Co valence states at ambient conditions are not affected by pressure. The Co Kβ emission spectra, on the other hand, revealed a gradual spin state transition of Co ions from a high-spin (S = 2) state at ambient pressure to a complete low-spin state (S = 0) at 40 GPa without crossing the intermediate spin state (S = 1). This can be well understood from our calculated phase diagram in which we consider the energies of the low spin, intermediate spin and high spin states of Co ions as a function of the anisotropic distortion of the octahedral local coordination in the layered oxide. We infer that a short in-plane Co-O bond length (<1.90 Å) as well as a very large ratio of Co-O/Co-O is needed to stabilize the IS Co, a situation which is rarely met in reality.
通过使用硬 X 射线吸收和发射光谱研究了具有层状 KNiF 型结构的混合 3d-5d 固态氧化物 SrCoIrO 中 Co-O 键长和 Co 离子自旋态对压力的响应。Co-K 和 Ir-L X 射线吸收光谱表明，在环境条件下 Ir 和 Co 的价态不受压力影响。另一方面，Co Kβ发射光谱显示 Co 离子的自旋态逐渐从环境压力下的高自旋（S=2）态转变为完全的低自旋态（S=0），在 40GPa 时没有经过中间自旋态（S=1）。从我们计算的相图中可以很好地理解这一点，我们考虑了 Co 离子的低自旋、中间自旋和高自旋态的能量作为各向异性扭曲的函数在层状氧化物中的八面体局部配位。我们推断，需要短的面内 Co-O 键长（<1.90Å）和非常大的 Co-O/Co-O 比来稳定 IS Co，这种情况在现实中很少见。
