Origin of Color Centers in the Perovskite Oxide CeAlO₃

Abstract

In view of the significant impact of color centers on the physical and chemical properties of materials, studies on the origin of such color centers are needed. In this article, detailed crystal structure analysis and compositional characterization of CeAlO3 was carried out by applying XRD, XPS, HRTEM, STEM‐EDS and ICP‐OES techniques. The results revealed that crystal defects may be the main cause of color centers. The existence of oxygen and aluminum vacancy was proved and confirmed by the application of XPS, ICP‐OES and STEM‐EDS characterization methods. Overall, it unlikely that a single crystal defect would generate the yellow‐green color of CeAlO3 crystals.

Synthesis of cerium aluminate by the mechanical activation of aluminum and ceria precursors and firing in controlled atmospheres

“…Still, the coexistence of CeAlO 3 with α‐Al 2 O 3 is not consistent with the stoichiometric ratio Al:Ce = 1:1 of the overall composition, thus suggesting a nonstoichiometric perovskite phase. In fact, Al‐deficient perovskites CeAl 1− y O 3− δ were reported by others 39 . Alternatively, one may consider a fraction of amorphous ceria in contact with alumina, which was reported at least for temperatures up to about 825°C 15…”

“…This temperature is still insufficient to eliminate the contents of α‐Al 2 O 3 formed during the previous long‐term milling step, confirming that α‐Al 2 O 3 is poorly reactive. The stability of Al‐deficient perovskite CeAl 1− y O 3− δ 39 may also explain the low driving force for the incorporation of the residual alumina content. Still, complete conversion was reported after firing at 1500°C 5 …”

“…However, the relative proportions of residual alumina and ceria may also depend on the tolerance of the perovskite phase to undergo deviations from the stoichiometric composition (e.g., CeAl 1− y O 3− δ 39 ) and reactivity of precursor oxides in the milled powder mixture, as demonstrated by the selective segregation of α‐Al 2 O 3 combined with CeAl 1− y O 3− δ (Figure 7).…”

“…In fact, Al-deficient perovskites CeAl O 3−δ were reported by others. 39 Alternatively, one may consider a fraction of amorphous ceria in contact with alumina, which was reported at least for temperatures up to about 825 • C. 15 Changes in firing schedules were also tried to obtain information on the effects of time, temperature, and humidity (Figure 7). These results showed that an increase in firing time did not contribute to minimize the secondary phase α-Al 2 O 3 .…”