EXAFS study of local structure at the alkali ions in superconducting K2\mathrm{K_2} RbC60,K2CsC60,Rb2CsC60\mathrm{RbC_{60}, K_2 CsC_{60}, Rb_2 CsC_{60}} , and Rb3C60\mathrm{Rb_3 C_{60}}

We have studied the local site assignment as well as the structural and dynamic properties of the alkali ions in superconducting K2RbC60, K2CsC60, Rb2CsC60, and Rb3C60 compounds by x-ray absorption fine structure (EXAFS) measurements at the alkali ions K, Rb, and Cs in the temperature range 14–300 K. In the ternary A2BC60 systems a strong preferential site occupation is observed, where the smaller alkali ions (A) are placed in tetrahedral sites and the larger ones (B) in octahedral sites. This site ordering allows a separate structural analysis of tetrahedral and octahedral sites. A quantitative analysis of the tetrahedral site (A) dopants yields the neighbor distances R(A-C), coordination numbers NC and second cumulants σ2. A similar analysis of the tetrahedral sites in Rb3C60 was performed by creating difference spectra with the K2RbC60 system. A multishell analysis of the octahedral sites (B) yields an off-center position of the B dopants. The off-center displacement scales with the size of the octahedral site and inversely with the ionic radius of the B dopant. A preferential displacement in the (1,1,1) direction is discussed in conjunction with possible carbon neighbor configurations at the octahedral sites. © 1996 The American Physical Society

EXAFS studies of superconducting A2BC60\mathrm{A_2BC_{60}} compounds

In the present work we have studied the X-ray absorption fine structure of the potassium and rubidium K-edges as well as the LIII-edge of caesium in K2RbC60, K2CsC60 and Rb2CsC60. A quantitative analysis for the first neighbour shell of the tetrahedral site (A) dopants yields the nearest neighbour distances R(At−C), coordination numbers Nc and second cumulants σ2. A multishell analysis of the octahedral sites (B) including the relevant scattering paths shows an off-center position of the (B) dopants

X-Ray Absorption Study of the High-Spin/Low-Spin Transition in [Fe(II)(bpp)2](BF4)2

We employed both the Fe-K XANES and EXAFS to study the HS/LS transition in [Fe(II)(bpp)2](BF4)2

EXAFS Study of Oxygen Distortions in Gd2CuO4\mathrm{Gd_2 CuO_4} as Function of Temperature and Pressure

We studied the temperature and pressure dependence of the oxygen distortion in the Cu-O planes of the Gd2CuO4 T-phase, employing the Gd-LIII EXAFS

X-Ray Absorption Study of the High-Spin/Low-Spin Transition in [Fe(II)(bpp)2](BF4)2\mathrm{[Fe(II)(bpp)_2](BF_4)_2}

We employed both the Fe-K XANES and EXAFS to study the HS/LS transition in [Fe(II)(bpp)2](BF4)2

X-Ray Absorption Study of the Local Structure At Potassium and Rubidium in K3−xRbxC60K_{3-x}Rb_xC_{60}

X-ray absorption fine structure (EXAFS and XANES) studies of the K-edges of potassium and rubidium in K3C60, K2RbC60 and Rb3C60 reveal the local structure and site preferences of the alkali metals. Both K and Rb ions on tetrahedral interstices exhibit regular positions with respect to the C60 neighbours in agreement with crystallographic data, while for Rb ions located on octahedral interstices an off-center position is found. The K2RbC60 sample exhibits a clear preferential site occupation of the octahedral site by Rb, which is also reflected by the lattice constant, and indications for structural rearrangement of the Rb ions on octahedral sites around 50 K

Local Structure of Ru in Ru-C60 and Ru-Fullerene Black Compounds

We studied the x-ray absorption fme structure (EXAFS) of Ru-C60 and Ru in fullerene black employing the K-edge of rutheniumn. The EXAFS analysis of the local structure in both systems allows the observation of small metallic particles and their modification caused by the effect of temperature and/or the usage of the samples as catalyst

EXAFS Study of Oxygen Distortions in Gd2CuO4 as Function of Temperature and Pressure

We studied the temperature and pressure dependence of the oxygen distortion in the Cu-O planes of the Gd2CuO4 T-phase, employing the Gd-LIII EXAFS

Local Structure of RuRu in Ru−C60\mathrm{Ru-C_{60}} and Ru-Fullerene Black Compounds

We studied the x-ray absorption fme structure (EXAFS) of Ru-C60 and Ru in fullerene black employing the K-edge of rutheniumn. The EXAFS analysis of the local structure in both systems allows the observation of small metallic particles and their modification caused by the effect of temperature and/or the usage of the samples as catalyst

EXAFS Study of the Local Iodine Structure in C60(I2)xC_{60} (I_2)_x and in C70(I2)xC_{70} (I_2)_x

Iodine LI,III - and K-edge XANES and EXAFS are employed to study the local structure of molecular iodine in C60(I2)x and C70(I2)x in the temperature range 20 K - 300 K. The K-edge EXAFS analysis, when compared with LIII-EXAFS, provides more detailed information about intra- and intermolecular distances