High‐Pressure Synthesis and Physical Properties of the Europium‐Substituted Barium Clathrate Ba 8− x Eu x Ge 43 □ 3 ( x ≤ 0.6)

The new clathrate Ba 8– x Eu x Ge 43 □ 3 ( x = 0.6) was synthesized at a pressure of 1 GPa and temperatures of up to 1220 K by means of a multi‐anvil device (Walker module) and a hydraulic 1000 ton press. X‐ray powder diffraction data indicate that the crystal structure of Ba 8– x Eu x Ge 43 □ 3 ( x = 0.6, space group $Ia{\bar 3}d$ , a = 21.2588(3) Å) corresponds to that of Ba 8 Ge 43 □ 3 . Measurements of the magnetic susceptibility of Ba 8– x Eu x Ge 43 □ 3 reveal Curie‐paramagnetic behaviour and prove that the electronic state of europium corresponds to 4 f 7 , i.e., Eu 2+ . Electrical resistivity shows a metal‐like temperature dependence and ρ (300) ≈ 2mΩ cm for x = 0.6. Heat capacity measurements reveal an upturn of c p / T(T) below 7 K that is attributed to magnetic interaction of the europium ions.