High pressure effects on U L₃x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd₁₁

Abstract

We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0–28.2 GPa) and single crystal x-ray diffraction (SXD) (0–20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K0 = 62(1) GPa and its pressure derivative, K0 = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

Study on the Correlation of U Valence States with U–U Distance in UPd2Cd20

“…As pressure increases, peak B increases while peak A decreases. The variation is quite different from the results on pressure effect of UCd 11 , whose a main peak in the spectra shifts toward high energy and becomes broad [18]. Therefore, the variation is expected to change U valence states as well as the variation observed in rare-earth L 3,2 -edges [17].…”

“…U valence states are recognized by the chemical shifts between the peaks A and B in the HERFD-XAS spectra. Peaks A and B correspond to the energy of U 3+ and U 4+ components, respectively, in comparison with the reference samples (UCd 11 for U 3+ [18] and UPd 3 for U 4+ [19]). These results show that uranium valence state of UPd 2 Cd 20 increases with applying pressure.…”

Valence instability across the magnetostructural transition in USb2

“…In the case of UCd 11 , no structural transition is observed, and the white line position increases linearly as a function of pressure. [29] In the cases of UPd 2 Al 3 , UC, and UN, structural transitions coincide with changes in the slope of the white line position with respect to pressure, though none of these compounds show the sudden, transient shift observed in our work. [30][31][32] UP, which undergoes structural transitions near P=10 GPa and P=28 GPa, shows a change in white line position across the P=10 GPa transition, but is constant across the latter structural transition.…”

Magnetic and Electronic Properties of the Ternary Compound U2T3Si5 (T = Rh, Ir)

“…Figure 4 shows HERFD-XAS spectra of the U L3-edge of U2Rh3Si5 and U2Ir3Si5, for the magnetically ordered state at 2 K and for paramagnetic state at 300 K, together with those of UCd11, UPd3, and UO2. Here, UCd11 [17], UPd3 [18], and UO2 [19] are the reference materials for HERFD-XAS spectra with U 3+ (5f 3 ), well-localized 5f states with metallic U 4+ (5f 2 ), and localized with insulating U 4+ (5f 2 ), respectively. The HERFD-XAS spectra of UCd11 and UO2 show well defined single-peak-like structures for U 3+ (5f 3 ) and U 4+ (5f 2 ), respectively.…”