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K. Kovnir, U. Stockert, S. Budnyk, Y. Prot, M. Baitinger, S. Paschen, A. Shevelkov, Y. Grin:
"Introducing a Magnetic Guest to a Tetrel-Free Clathrate: Synthesis, Structure, and Properties of Eu_xBa_8-xCu₁₆P₃₀ (0 ≤ x ≤ 1.5)";
Inorganic Chemistry, 50 (2011), S. 10387 - 10396.

The europium-containing clathrate-I EuxBa8 xCu16P30 was synthesized
from the elements. Powder X-ray diffraction in combination with energy
dispersive X-ray absorption spectroscopy (EDXS) and metallographic studies showed
the homogeneity range with xe1.5. Determination of the crystal structure confirmed
the presence of an orthorhombic superstructure of clathrate-I and revealed that Eu
atoms exclusively resided in small pentagonal-dodecahedral cages. Magnetic measurements
together with X-ray absorption spectroscopy are consistent with a 4f7 (Eu2+)
ground state for EuxBa8 xCu16P30. Below 3 K the Eu moments order antiferromagnetically.
Resistivity measurements revealed metallic behavior of the investigated
clathrate, in line with the composition deviating from the Zintl counting scheme.
Local vibrations of the guest atoms inside the cages are analyzed with the help of specific heat investigations.

http://dx.doi.org/10.1021/ic201474h