Europium silicides and germanides of the EuM2X2 type

Valence instability of europium in EuCo2Si2

“…Eu atoms are located in the 2a position (0 0 0), Co in the 4d position (0 1/2 1/4) and Si in the 4e position (0 0 z) [6]. We obtained z = 0.371(3), which is slightly different from the value 0.375(2) reported in Ref.…”

“…[10]. Our lattice parameters (a = 3.9194(7)Å, c = 9.826(2)Å) are slightly smaller than those of Mayer et al [5,6] other RCo 2 Si 2 compounds, where R = rare earth [5,11], no clear anomaly is seen for EuCo 2 Si 2 , which indicates a predominant trivalent europium component.…”

“…They can be of the same or close stoichiometry to the matrix but exhibit a local disorder, for example between Co and Si atoms. Such disorder was suggested to be possible for EuNi 2 Si 2 [6]. A change of stoichiometry in EuNi 2−x Si 2+x and EuCu 2−x Si 2+x has a strong influence on the europium valence [33,34], so local exchange of silicon and cobalt in EuCo 2 Si 2 can have a similar influence.…”

“…The valence change upon applied pressure is associated with the barocaloric effect and, therefore, EuNi 2 (Si 0.15 Ge 0.85 ) 2 was recently evaluated as a promising candidate for cooling by application of pressure [4]. EuCo 2 Si 2 was studied by Mössbauer spectroscopy [5][6][7], X-ray absorption spectroscopy [8] and measurements of the thermoelectric force [9]. Results of Felner et al indicate a heterogeneous mixed valence state of europium (85% of Eu 3+ , 15% of Eu 2+ ) [5,7], whereas investigations of Levin et al reveal a pure trivalent europium component [8].…”

Ternary BaAl4-type derivative structures

“…RTSi 3 compounds with BaA14-type derivative structure have been reported for CeCoSi 3 (Bodak & Gladyshevskii, 1970b) and EuNiSi 3 (Mayer & Felner, 1977); however, without further information it is impossible to assign their structures to this type or any other R TM~ type.…”