Inversion of 4f-states in CeB₆ thermally excited at 430 K

Abstract

The 4f states of Ce in a typical Kondo crystal, CeB(6), are split into an excited state Gamma(7) and the ground state Gamma(8), with an excitation energy at 560 K. The electron-density distribution of the thermally excited state was measured at 430 K using a four-circle diffractometer equipped with a small furnace. In contrast to the previous results at lower temperature, electrons are transferred from B(6) to Ce at 430 K. X-ray atomic-orbital analysis revealed that the 5d-Gamma(8) orbitals (the energy level of which is similar to that of the B-2p orbitals) are fully occupied and the 4f-Gamma(7) orbitals are more populated than the 4f-Gamma(8) orbitals. Fully occupied 5d-Gamma(8) makes the 4f-Gamma(8) states unstable and the energy levels of 4f-Gamma(7) and 4f-Gamma(8) are inverted.

X-ray atomic orbital analysis of 4f and 5d electron configuration of SmB6 at 100, 165, 230 and 298 K

“…4f-EDD was first analyzed by Tanaka, Kato & O " nuki (1997) based on the real 4f orbitals in CeB 6 at 165 K. By employing the complex 4f orbitals which are calculated based on the spin-orbit interaction, the 4f-EDD of CeB 6 was analysed at 100, 165, 230 and 298 K (Tanaka & O " nuki, 2002). In our previous work on CeB 6 (Makita et al, 2007(Makita et al, , 2008 5d orbitals were also occupied above room temperature.…”

5d and 4f electron configuration of CeB6 at 340 and 535 K

“…In our previous study (Makita et al, 2007; hereinafter referred to as MTOT) the electron-density distribution (EDD) in CeB 6 was measured at 430 K and analyzed with the XAO analysis method (Tanaka et al, 2008) and several interesting facts were found. At high temperature electrons were transferred from B 2p x (= p y ) to the Ce 5d(j = 5/2)À 8 orbitals, and the 4f-À 7 state, which is above 4f-À 8 in energy at 298 K, was more populated than the 4f-À 8 orbitals.…”

XAO Analysis - AO's and Their Populations in Crystal Fields

“…Thus, the electron population above room temperature became very interesting. Since the energy gap between the two 4f5/2 orbitals is about 500 K, the X-ray intensities were measured at 430 K expecting for 4f5/2  to be more populated (Makita et al, 2007). The results were surprising.…”

“…Lobes of 4f5/28 extend along <100> directions while those of 4f5/27 orbitals along <110> and <111> as illustrated in Fig. 7 of Makita et al (2007). …”

“…Since the energy gap between 4f5/28 and 7 was reported to be 530-560 K (Loewenhaupt et al, 1985;Zirngiebl et al, 1984), XAO analysis at 430 K was performed to observe more electrons in 7 (Makita et al, 2007). For details of the high-temperature diffraction equipment, see PhD thesis of Makita (Makita, 2008).…”