Driving the Europium Valence State in EuCo2As2 by External and Internal Impact

Abstract

The pressure effect on the europium valence state was investigated in the series of samples based on the EuCo 2 As 2 compound by means of X-ray absorption spectroscopy. The pressure dependence of the europium valence was obtained in a wide range of applied and chemical pressures; the latter was reached by substituting Ca for Eu. The correlation between these two ways to impact the Eu valence was established. The data obtained allow estimating the pressure effect on the electronic structure of EuCo 2 As 2 and other related properties such as the change in magnetic ordering.

X-ray absorption spectroscopy and Eu3+-emission characteristics in GaAs/SnO2 heterostructure

“…Eu 3+ , partly located in the nanocrystal surface region, reduced to Eu 2+ , is internally stabilized when samples were exposed to X-ray radiation, being an alternative approach for oxidation state manipulation and a potential application of Ga 2 O 3 as an X-ray storage phosphor. Europium oxidation state was investigated by XANES concerning the dependency on external and chemical pressure in Ca 1−x Eu x Co 2 As 2 [17]. The Eu valence increases with pressure and Ca concentration, agreeing with f-d hybridization in determination of the electronic structure; besides, it changes almost linearly with applied pressure.…”

An Unusual Valence State: Trivalent Europium in Intermetallic Eu2Ir3Al9

“…In the field of intermetallics, Eu and Yb are usually found as formally divalent cations . Compounds containing elements that exhibit two valence states sometimes show interesting physical properties such as valence fluctuations (e.g., CeAl 3 , CeRu 1− x Ni x Al, Yb 4 Pt 9 Ga 24 , or EuCu 2 Si 2 ), pressure‐dependent valence shifts (e.g., EuCo 2 As 2 , YbAl 3 ), or very rarely observed valence‐phase transitions (e.g., Eu(Ir 1− x Pd x ) 2 Si 2 , Eu 2 Pt 6 Al 15 ). In the case of the europium compounds, the number of divalent compounds exceeds the trivalent ones by far.…”

“…[8] In the field of intermetallics, Eu and Yb are usually found as formally divalent cations. [9] Compounds containing elements that exhibit two valence states sometimes show interesting physical properties such as valence fluctuations (e.g.,C eAl 3 , [10] CeRu 1Àx Ni x Al, [11] Yb 4 Pt 9 Ga 24 [12] ,o r EuCu 2 Si 2 [13] ), pressure-dependent valence shifts (e.g., EuCo 2 As 2 , [14] YbAl 3 [15] ), or very rarely observed valence-phase transitions (e.g.,E u(Ir 1Àx Pd x ) 2 Si 2 , [16] Eu 2 Pt 6 Al 15 [17] ). In the case of the europium compounds, the number of divalent compounds exceeds the trivalent ones by far.R are examples for the latter oxidation state are the binaryc ompounds EuRh 2 , [18] EuIr 2 , [18] EuNi 5 , [18] Eu 2 Ni 17 , [18] EuPd 3 , [18] and EuPt 5 [18] as well as the ternary borides EuRu 4 B 4 [19] and EuRuB 4 , [19] the silicides EuCo 2 Si 2 [20] and EuRu 2 Si 2 [20b] or the phosphide Eu 2 Co 12 P 7 .…”

Temperature induced valence phase transition in intermediate-valent YbPd2Al3

“…21,22 In EuPtP two new pressure induced valence ordered structures were observed, 23 while EuCo 2 As 2 (ref. 24) and YbAl 3 (ref. 25) exhibit pressure dependent shis of their valence.…”