Solid‐state synthesis of multicomponent equiatomic rare‐earth oxides

Abstract

Phase formation in multicomponent rare-earth oxides is determined by a combination of composition, sintering atmosphere, and cooling rate. Polycrystalline ceramics comprising various combinations of Ce, Gd, La, Nd, Pr, Sm, and Y oxides in equiatomic proportions were synthesized using solid-state sintering. The effects of composition, sintering atmosphere, and cooling rate on phase formation were investigated. Single cubic or monoclinic structures were obtained with a slow cooling of 3.3°C/min, confirming that rare-earth oxides follow a different structure stabilization process than transition metal high-entropy oxides. In an oxidizing atmosphere, both Ce and Pr induce a cubic structure, while only Ce plays that role in an inert or reducing atmosphere. Samples without Ce or Pr develop a single monoclinic structure. The structures formed at initial synthesis may be converted to a different one, when the ceramics are annealed in an additional atmosphere. Phase evolution of a five-cation composition was also studied as a function of sintering temperature. The binary oxides used as raw materials completely dissolve into a single cubic structure at 1450°C in air. K E Y W O R D S phase transformations, rare earths, reaction sintering How to cite this article: Pianassola M, Loveday M, McMurray JW, Koschan M, Melcher CL, Zhuravleva M. Solid-state synthesis of multicomponent equiatomic rare-earth oxides. J Am Ceram Soc.

Effects of composition and growth parameters on phase formation in multicomponent aluminum garnet crystals

“…A surprising phase stabilization and attractive functional properties have been reported for oxides containing five cations that fractionally occupy the same crystallographic site (Rost et al, 2015;Musico ´et al, 2020). Such complex compositions are usually called 'high-entropy' or 'multicomponent' (Djenadic et al, 2017;Pianassola, Loveday, McMurray et al, 2020;Karati et al, 2021;Sun et al, 2020). Admixing two or three elements in garnet crystals has been shown to improve scintillation properties (Kamada et al, 2011(Kamada et al, , 2014Prusa et al, 2013;Chewpraditkul et al, 2018).…”

“…The phase stabilization of multicomponent oxides has been attributed to an entropy-driven mechanism (Rost et al, 2015), but the composition and synthesis method can also affect phase formation in polycrystalline samples (Djenadic et al, 2017;Pianassola, Loveday, McMurray et al, 2020). In the case of crystals grown via directional solidification, the formation of a single phase also depends on melt congruency and elemental segregation.…”

Crystal Growth and Elemental Homogeneity of the Multicomponent Rare-Earth Garnet (Lu1/6Y1/6Ho1/6Dy1/6Tb1/6Gd1/6)3Al5O12

“…Following the general trend of high-entropy metallic alloys, the possibility of obtaining exceptional functional properties has inspired the investigation of high-entropy oxides. , A few RE-based high-entropy polycrystalline ceramics have been reported including sesquioxide, , silicate, , zirconate, phosphate, aluminum perovskite, and aluminum garnet structures. In previous reports, the availability of high-entropy oxides was restricted to the synthesis methods for ceramics or thin films .…”

Puffing ultrathin oxides with nonlayered structures

“…S2) verify the structures of rare-earth oxides, indicative of Sm 2 O 3 , Gd 2 O 3 , Er 2 O 3 , and Yb 2 O 3 with the C-type cubic bixbyite structure and CeO 2 and Pr 4 O 7 with the cubic fluorite structure; the corresponding atomic structures are shown in Fig. 2 (F, L, R, X, AE, and AK) ( 34 – 36 ). It is worth mentioning that high-entropy oxides (HEOs) ( 37 – 39 ) of (ErGdYbSm 1.2 Y 0.8 ) 2 O 3 and (CoMnNiCrFe) 3 O 4 with unique structural characteristics were also prepared by this method.…”

“…The x-ray diffraction (XRD) pattern (fig. S1) reveals that the ultrathin Nd 2 O 3 porous nanosheet belongs to the A-type hexagonal structure ( 34 ), which is verified by the high-resolution TEM (HRTEM) image and fast Fourier transform (FFT) image pattern with a positive hexagonal dot matrix ( Fig. 1F , inset).…”