Synthesis and Theoretical Investigations of the Solid Solution CeRu_1–xNi_xAl (x = 0.1–0.95) Showing Cerium Valence Fluctuations

Abstract

Members of the solid solution series of CeRu(1-x)Ni(x)Al can be obtained directly by arc melting of the elements. The presented compounds with 0.1 ≤ x ≤ 0.85 crystallize in the orthorhombic space group Pnma (No. 62) in the LaNiAl structure type, while for 0.9 ≤ x ≤ 1, the hexagonal ZrNiAl-type structure is found. The orthorhombic members exhibit an anomaly in the trend of the lattice parameters as well as an interesting behavior of the magnetic susceptibility, suggesting that the cerium cations exhibit no local moment. Besides the mixed-valent nature of the cerium cations, valence fluctuations along with a change in the cerium oxidation state depending on the nickel content have been found. The oxidation state has been determined from the magnetic data and additionally by XANES. Density functional theory calculations have identified the shortest Ce-Ru interaction as decisive for the stability of the orthorhombic solid solution.

Gradual Cerium Valence Change in the Solid Solution CeRu1–xPdxAl (x = 0.1–0.9)

“…For X = Al, the majority of these compounds crystallizes in one of the following prototypic crystal structures: ZrNiAl and TiNiSi are the most prominent ordered representatives along with MgZn 2 , MgCu 2 , and KHg 2 as examples of structures where the T element and usually Al are mixed on one crystallographic site. A rare example of an ordered equiatomic composition with only four reported ternary aluminum representatives (LaNiAl,2 LaRhAl,3 CeRhAl,3,4 CeRuAl4,5) is the LaNiAl type structure, which was also found for the solid solution CeRu 1– x Ni x Al for a wide range of x 6…”

Magnetic Properties of theRE2Pt6X15(RE= Y, La–Nd, Sm, Gd–Lu;X= Al, Ga) Series

“…Especially cerium containing compounds have gathered a lot of attention since they exhibit various highly interesting physical features, e.g. Kondo behavior (CeAl 2 , CeAuAl), superconductivity (CeCu 2 Si 2 , CeCoIn 5 ), heavy fermion behavior (CeAl 3 ), colossal magneto resistance (CMR, Ce 3 Cu 3 Sb 4 ) or valence fluctuations (CeRu 1– x Ni x Al, CeRu 1– x Pd x Al). These phenomena are caused by the two possible oxidation states, Ce 3+ (4 f 1 ) being paramagnetic and Ce 4+ (4 f 0 ) being diamagnetic.…”

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.…”