Evidence of Eu2+ 4f electrons in the valence band spectra of EuTiO3 and EuZrO3

Abstract

We report on optical band gap and valence electronic structure of two Eu2+-based perovskites, EuTiO3 and EuZrO3 as revealed by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy. The data show good agreement with the first-principles studies in which the top of the valence band structure is formed by the narrow Eu 4f7 electron band. The O 2p band shows the features similar to those of the Ba(Sr)TiO3 perovskites except that it is shifted to higher binding energies. Appearance of the Eu2+ 4f7 band is a reason for narrowing of the optical band gap in the title compounds as compared to their Sr-based analogues.

Revisiting the fascinating properties of EuTiO 3 and its mixed crystals with SrTiO 3 : Possible candidates for novel functionalities

“…It should be mentioned here that the corresponding empty d states of the transition metals in EuZrO 3 and EuHfO 3 lie much higher in energy and as a consequence these oxides have significantly larger band gaps and are yellow and white, respectively [25]. The theoretically derived band gap is in rough agreement with conductivity measurements on thin films [26], our own conductivity data on bulk ceramic samples [27] as well as experimental results obtained by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy [28].…”

“…This latter conclusion has been supported experimentally in Refs. [14,28], whereas the TA zone boundary instability has been confirmed by inelastic x-ray scattering [15].…”

Observation of giant magnetocaloric effect in EuTi 1-x Cr x O 3

“…But the values of µ eff also belong to a reasonable region (µ = 7 ± 1 µ B ), which are found to be consistent to the free ion as previously reported [27]. The localized 4f moments on the Eu 2+ (S = 7/2, L= 0) sites order, and the Eu 2+ 4f 7 band is a reason for narrowing of the optical band gap in the title compounds [28]. 3(b-d).…”

Observation of giant magnetocaloric effect in EuTiO3

“…The effective magnetic moment  eff =7.596  B is obtained based on the value of C m . The localized 4f moments on the Eu 2+ (S = 7/2, L= 0) sites order [21], and the Eu 2+ 4f 7 band is a reason for narrowing of the optical band gap in the title compounds [22].The value of the Eu 2+ magnetic moment (μ = 7 ± 1 μ B ) was found to be consistent to the free ion as previously reported [21]. The value of  p is positive and equals to 3.2 K, which implies that the EuTiO 3 compound is a 4 weak intiferromagnetic.…”