Journal of Alloys and Compounds 369 (2004) 252–255 Ce valence in La 0.47 Ce 0.20 Ca 0.33 MnO 3 J.E. Gayone a,∗ , M. Abbate b , G. Alejandro c , D.G. Lamas d , M. Tovar c , G. Zampieri c a Institute for Storage Ring Facilities, University of Aarhus, DK-8000 Aarhus C, Denmark b Departamento de Fisica, UniversidadFederal de Parana, Caixa Postal 19091, 81531-990 Curitiba PR, Brazil c Centro Atómico Bariloche, CNEA, Av. Bustillo 9500, 8400 San Carlos de Bariloche, Argentina d Centro de Investigaciones en Sólidos, CITEFA-CONICET, J.B. de La Salle 4397, 1603 Villa Martelli, Argentina Abstract The valence of Ce in La 0.47 Ce 0.20 Ca 0.33 MnO 3 is analyzed using X-ray absorption and photoemission spectroscopies. These spectroscopies are very sensitive to the 4f occupation and thereby to the Ce valence. We find that both tetra- and trivalent Ce ions are present, estimating their percentages in 65 and 35%, respectively. © 2003 Elsevier B.V. All rights reserved. Keywords: La 0.47 Ce 0.20 Ca 0.33 MnO 3 ; X-ray absorption; XPS 1. Introduction It has been observed that in manganite systems La 1-x D x MnO 3 (D = Ca, Sr, Ba) the partial replacement of lanthanum by yttrium or a rare earth (such as Pr or Tb) gives rise to a variety of different phenomena: magnetic frustration [1–2], spin-glass-like behavior [3], and elec- tronic phase separation [4]. The main changes introduced in the system are the bending of the Mn–O–Mn angle and, if the divalent cation is replaced, the change of the doping level. Cerium is singular among the rare-earth ions in that it can adopt two valences: 3 and 4, what constitutes and ad- ditional degree of freedom. The knowledge of the Ce va- lence is, therefore, very important to understand the physical properties of the compound. Several studies of the Ce-doped La–Ca manganites have appeared recently in the literature. The cases studied are shown in Fig. 1 in the form of a ternary-compound phase diagram. Mandal and Das [5], Geb- hardt et al. [6], Raychadhuri et al. [7], and Philip and Kutty [8] have reported the preparation of La 1-x Ce x MnO 3 with 0 ≤ x ≤ 0.8. These authors interpret their results assuming that the Ce ions are tetravalent, and, therefore, that some Mn ∗ Corresponding author. E-mail address: gayone@cab.cnea.gov.ar (J.E. Gayone). ions are divalent; this means that LaMnO 3 is doped with electrons instead of holes. Ganguly et al. [9] have ques- tioned these results arguing that these compounds segre- gate into La 1-d MnO 3 and CeO 2 . The key problem seems to be the large ionic radius of the Mn 2+ ions, which ren- ders the structure unstable and, as a consequence, the seg- regation very likely. The other edge of the phase diagram, Ca 1-x Ce x MnO 3 , has been studied by Maigman et al. [10] and Zeng et al. [11]. Also these authors interpret their results assuming that the Ce ions are tetravalent. In this case, how- ever, the electron doping of CaMnO 3 leads to the formation of Mn 3+ ions, which fit well in the perovskite structure and do not give rise to any instability. The only case studied in the interior of the triangle is that of La 0.7 Ce 0.15 Ca 0.15 MnO 3 by Wu et al. [12]. In this work the authors ascribe a peak in the neutron diffraction data to the ordering of the Ce spins opposite to that of the Mn ions. This study is, there- fore, the only one that reports the existence of trivalent Ce ions. In this paper we report an analysis of the Ce valence in La 0.47 Ce 0.20 Ca 0.33 MnO 3 using X-ray absorption (XAS) and photoemission (XPS) spectroscopies. Although this com- pound falls in the gray region of the phase diagram, meaning that all the Ce ions can be tetravalent without implying the formation of Mn 2+ ions, we will show that both tetra- and trivalent Ce ions are present. 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.09.051