Modifying the valence phase transition in Eu2Al15Pt6 by the solid solutions Eu2Al15(Pt1−x T x )6 (T = Pd, Ir, Au; x = 1/6)

Abstract

Abstract The solid solutions Eu2Al15(Pt1−x T x )6 with T = Pd, Ir, Au and x = 1/6 were prepared by arc-melting the stoichiometric mixture of the elements, and subsequent annealing. For x = 1/6, all three solid solutions adopt the same structure type as Eu2Al15Pt6 according to powder X-ray diffraction data. Since the platinide Eu2Al15Pt6 exhibits a (3 + 1)D modulated structure (approximant in space group P121/m1), only the averaged hexagonal unit cell (P63/mmc, Sc0.6Fe2Si4.9 type) was refined by the Rietveld method. Scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy (SEM/EDX) showed that the degree of substitution is in line with the weighed amounts. For values of x > 1/6, no phase-pure samples could be obtained. The results of the magnetic susceptibility measurements indicate that the isoelectronic substitution of Pd for Pt lowers the temperature of the first-order valence phase transition from T trans = 45 K in Eu2Al15Pt6 to T trans = 42 K in Eu2Al15(Pt5/6Pd1/6)6. For Eu2Al15(Pt5/6Ir1/6)6 and Eu2Al15(Pt5/6Au1/6)6 a change in the electronic situation occurs since the Ir substituted compound exhibits one electron less compared to the pristine Pt compound, while Eu2Al15(Pt5/6Au1/6)6 has one additional electron. As a consequence, Eu2Al15(Pt5/6Ir1/6)6 shows a higher valence phase transition temperature of T trans = 52 K while for Eu2Al15(Pt5/6Au1/6)6 no such transition is obvious.