It is reported that valence instabilities are an interesting and general phenomenon for rare earth ions in their compounds, for example, mixed valences, valence fluctuations, and
surface valence transitions [24–27]. Our present work provides an opportunity to study further valence instabilities of Eu in EuTiO3 and their resultant properties. Figure 3 HRXRD longitudinal scans and XRD pole figure. (a) Symmetric HRXRD longitudinal ω- 2θ scans of the as-grown and postannealed EuTiO3 films on SrTiO3(001) substrate. (b) XRD 211 pole figure of the as-grown sample. The elemental composition of the films was then analyzed by XPS, which was taken within a binding energy scan range from 0 to 1,300 eV. No signals pertinent to K+ cation can be found, indicating that the films have no incorporation of K from the solvent. The Eu 3d and Ti 2p core-level XPS spectra of the as-grown sample are shown
in Figure 4a,b, respectively. ABT-263 chemical structure The LCL161 datasheet results clearly exhibit that the as-grown sample consists of mixed Eu2+, Eu3+, and Ti4+ cations, in agreement with the peak positions of the cations shown in the XPS spectra from other studies [25–29]. The presence of Eu3+ indicates the necessity of anion excess in the as-grown films for charge balance and may affect the crystal lattice and magnetic properties of the films, which will be discussed later on. The Eu learn more 3d core-level XPS spectra of the annealed sample are shown in Figure 4a, which reveals a reduction of Eu3+ quantity. The Ti 2p core-level XPS spectra of the annealed sample not only are dominated by the Ti4+ contribution but also plausibly exhibit the Ti3+
shoulders, as shown in Figure 4b. These results reflect a necessity to lose part of the ionic charge during the annealing process for charge compensation. Further investigations are necessary to understand the chemical details of the films and annealing process. Figure 4 XPS spectra of the as-grown and postannealed samples. (a) A comparison of the Eu 3d core-level XPS spectra between the as-grown and postannealed samples. (b) Ti 2p core-level XPS spectra of the as-grown and postannealed Sulfite dehydrogenase samples. It is important to realize the possible inclusion of water or hydroxyl in the as-grown films. Such issues have been reported in various perovskites prepared hydrothermally [30–32]. These impurities can contribute to charge balance in the as-prepared perovskites and be removed by annealing to produce defects, which when coupled with a metal can account for charge compensation [30, 31]. Thus, our films were studied by FTIR. Figure 5 shows the FTIR spectra of the as-grown and postannealed samples for a comparison. No peaks pertinent to water or hydroxyl can be seen and resolved from the spectra; hence, the presence of water or hydroxyl and their resultant charge balance/compensation mechanisms are excluded in our films.