Mixed Valence of Ce and Its Consequences on the Magnetic State of Ce9Ru4Ga5: Electronic Structure Studies

We report on X-ray photoelectron spectroscopy (XPS) and ab initio electronic structure investigations of a novel intermetallic material Ce 9 Ru 4 Ga 5 . The compound crystallizes with a tetragonal unit cell (space group I4 m m ) that contains three inequivalent Ce atoms sites. The Ce 3 d core level XPS spectra indicated an intermediate valence (IV) of selected Ce ions, in line with the previously reported thermodynamic and spectroscopic data. The ab initio calculations revealed that Ce1 ions located at 2 a Wyckoff positions possess stable trivalent configuration, whereas Ce2 ions that occupy 8 d site are intermediate valent. Moreover, for Ce3 ions, located at different 8 d position, a fractional valence was found. The results are discussed in terms of on-site and intersite hybridization effects.

Temperature induced valence phase transition in intermediate-valent YbPd2Al3

A temperature induced valence phase transition from Yb3+ at higher temperatures to Yb2+ at lower temperatures was observed at T = 110(1) K for intermetallic YbPd2Al3.

Evolution of Ce-Valence in Ce-Rh-Si Compounds: Intermediate Valence in CeRh6Si4

We synthesized polycrystalline samples of CeRh6Si4 and investigated its physical properties by means of magnetic susceptibility, specific heat and electrical resistivity measurements as well as LIII X-ray absorption spectroscopy. All results evidence an intermediate-valent (IV) Ce state with a valence close to 3.2 and a characteristic energy of about 300 K. Accordingly, we observe a Fermi liquid ground state at low temperatures with a slightly enhanced Sommerfeld coefficient γ = 28 mJ/molK2. Using presently available data on different compounds, we analyze the evolution of the Ce valence in the Ce-Rh-Si ternary phase diagram. The expected correlation with the distance to nearest Ce-ligands can be discerned. Thus, the evolution from a trivalent Ce3+ state in CeRh3Si2 to an IV state in CeRh6Si4 is related to a shortening of both the Ce-Rh and Ce-Si bonds in the first coordination sphere of Ce.

High-pressure high-temperature decomposition of CeCoGa to the Laves phases CeCo0.58Ga1.42, CeCo0.72Ga1.28, and CeCo2

The monoclinic intermediate-valent gallide CeCoGa decomposes under high-pressure (HP) (9.5 GPa) high-temperature (HT) (1470 K) conditions into the Laves phases CeCo0.58Ga1.42 (MgCu2 type), CeCo0.72Ga1.28 (MgZn2 type; major product phase), and CeCo2 (MgCu2 type). The structures of the ternary Laves phases were refined from single crystal X-ray diffractometer data: Fd3̅m, a=778.3(1) pm, wR2=0.0310, 63 F2 values, five variables for CeCo0.58(3)Ga1.42(3) and P63/mmc, a=547.24(5), c=858.76(7) pm, wR2=0.1009, 195 F2 values, 13 variables for CeCo0.72(1)Ga1.28(1). Partial substitution of cobalt by gallium leads to a significant increase of the distances within the tetrahedral network: 253 pm Co–Co in CeCo2 as compared to 275 pm in CeCo0.58(3)Ga1.42(3) and 265–277 pm in CeCo0.72(1)Ga1.28(1). The crystal chemical consequences are briefly discussed.

The modulated structure of intermediate-valent CeCoGa

CeCoGa was synthesized by melting of the elements in an arc-melting furnace as well as in a sealed niobium tube in an induction furnace. A further annealing step improves the purity and crystallinity of the samples significantly. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Already at room temperature CeCoGa crystallizes in a superstructure of the HT-CeCoAl type. This superstructure can be described in the (3+1)D superspace group

Intermediate-valent CeCoAl – a commensurate modulated structure with short Ce–Co distances

CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group

Ternary Antimonides RE4T7Sb6 (RE=Gd–Lu; T =Ru, Rh) with Cubic U4Re7Si6-type Structure

The ternary antimonides RE4T7Sb6 (RE=Gd-Lu; T =Ru, Rh) have been synthesized from the elements by arc-melting and subsequent annealing in an induction furnace. The samples have been characterized by powder X-ray diffraction. Four structures were refined on the basis of single-crystal X-ray diffractometer data: U4Re7Si6 type, space group Im3m with a=862.9(2) pm, wR2=0.0296, 163 F2 values for Er4Ru7Sb6; a=864.1(1) pm, wR2=0.1423, 153 F2 values for Yb4Ru7Sb6; a=872.0(2) pm, wR2=0.0427, 172 F2 values for Tb4Rh7Sb6; and a=868.0(2) pm, wR2=0.0529, 154 F2 values for Er4Rh7Sb6, with 10 variables per refinement. The structures have T1@Sb6 octahedra and slightly distorted RE@T26Sb6 cuboctahedra as building units. The distorted cuboctahedra are condensed via all trapezoidal faces, and this network leaves octahedral voids for the T1 atoms. The ruthenium-based series of compounds was studied by temperature-dependent magnetic susceptibility measurements. Lu4Ru7Sb6 is Pauli-paramagnetic. The antimonides RE4Ru7Sb6 with RE=Dy, Ho, Er, and Tm show Curie-Weiss paramagnetism. Antiferromagnetic ordering occurs at 10.0(5), 5.1(5) and 4.0(5) K for Dy4Ru7Sb6, Ho4Ru7Sb6 and Er4Ru7Sb6, respectively, while Tm4Ru7Sb6 remains paramagnetic. Yb4Ru7Sb6 is an intermediate-valent compound with a reduced magnetic moment of 3.71(1) μB per Yb as compared to 4.54 μB for a free Yb3+ ion