Pressure Dependence of the Second-Order Valence Phase Transition in Eu2Al15Pt6 and the Solid Solutions Eu2Al15(Pt5/6T1/6)6 (T = Pd, Ir, Au)

Abstract

Eu2Al15Pt6, synthesized by arc-melting, was shown to exhibit a second-order valence phase transition around 45 K, where the divalent Eu atoms get trivalent below the transition temperature Ttrans. Substitution of Al by Ga in the solid solution Eu2(Al1–xGax)15Pt6 leads to the vanishing of the valence phase transition at low values of x, while substitution on the Pt position, according to Eu2Al15(Pt5/6T1/6)6 with T = Pd, Ir, or Au, leads to shifts of the transition temperatures. These substitutions can be considered to superimpose either chemical or electronic pressure, leading to the question of whether the application of physical pressure also has an influence on the valence change. Pressure-dependent magnetic susceptibility measurements have been conducted on Eu2Al15Pt6 and the three solid solutions Eu2Al15(Pt5/6T1/6)6 with T = Pd, Ir, and Au. In line with the expectations, the valence phase transitions under pressure occur at significantly higher temperatures, e.g., Ttrans(Eu2Al15Pt6@1.0 GPa) = 147(1) K, compared to ∼45 K at ambient pressure. Eu2Al15(Pt5/6Au1/6)6 does not exhibit a transition at ambient pressure, but interestingly, already at small pressures, the typical anomaly of a valence phase transition is observed in the susceptibility data.