Crystal Growth and Elemental Homogeneity of the Multicomponent Rare-Earth Garnet (Lu_1/6Y_1/6Ho_1/6Dy_1/6Tb_1/6Gd_1/6)₃Al₅O₁₂

Abstract

High-entropy aluminum garnets were grown as bulk single crystals using the micro-pulling-down method, taking the synthesis of complex ceramics a step further from the conventional preparation of polycrystalline materials. We studied the effects of growth parameters on the elemental distribution in high optical quality crystals of (Lu1/6Y1/6Ho1/6Dy1/6Tb1/6Gd1/6)3Al5O12 containing six cations (yttrium and rare-earths) taken in equimolar amounts. A single garnet structure was confirmed by powder X-ray diffraction. Electron microprobe measurements were obtained to correlate the radial distribution of rare-earth elements with pulling rates and molten zone height. The nature of the elemental distribution in the radial direction was associated with ionic radius: smaller rare-earths concentrated in the center of the crystal, while larger rare-earths segregated toward the outer edge of the cylindrical crystal. Faster pulling rates led to a flattening of the concentration profiles toward the nominal concentration, promoting a more homogeneous radial elemental distribution, while varying the molten zone height did not have a significant effect. The demonstrated success with crystal growth enables the practical availability of single crystals of multicomponent aluminum garnets for further discovery of new phenomena and applications.

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

“…Crystal C is a single garnet phase (space group Ia3d) and the lattice parameter is larger in the outer surface [12.0703 (3) A ˚] than in the center [12.0516 (4) A ˚], as seen in Table S1. This indicates a segregation of larger REs to the outer surface of the crystals, which is discussed in x3.3 and has been observed previously in multicomponent aluminum garnet crystals grown via the mPD method (Pianassola, Loveday, Chakoumakos et al, 2020). The outer surface of crystal I is also a single garnet phase (space group Ia3d) and has a larger unit-cell parameter [12.0892 (2) A ˚] than that of crystal C, which is expected since the AIR of composition I is larger than that of composition C (Table 1).…”

“…A molten-zone height of $200 mm was maintained for all growth experiments by adjusting the power of the RF generator. A previous publication includes details about the mPD method and the crystal growth set-up used (Pianassola, Loveday, Chakoumakos et al, 2020).…”

“…Therefore, multicomponent crystals could lead to further improvement in performance for radiation detection in medical imaging and homeland security applications. To date, only two multicomponent aluminum garnet compounds have been reported with five or more rare-earth (RE) elements, one synthesized as a polycrystalline ceramic (Chen et al, 2020) and one as a single crystal (Pianassola, Loveday, Chakoumakos et al, 2020). Further study on composition design and crystal growth of garnets containing multiple REs is needed to establish a correlation between composition and phase formation, and to guide future investigation into fundamental and functional properties in single crystals.…”

“…In the case of crystals grown via directional solidification, the formation of a single phase also depends on melt congruency and elemental segregation. While there are several publications on multicomponent oxide thin films (Meisenheimer et al, 2017;Kotsonis et al, 2020Kotsonis et al, , 2018Sivakumar et al, 2018;Liang et al, 2021;Jacobson et al, 2021;Patel et al, 2020;Nguyen et al, 2020;Braun et al, 2018;Sharma et al, 2018Sharma et al, , 2021Chen et al, 2021;Kirnbauer et al, 2019), only a few reports demonstrate the growth and phase formation in multicomponent oxide bulk crystals (Pianassola, Loveday, Chakoumakos et al, 2020;Pianassola et al, 2021;Greculeasa et al, 2020;Liu et al, 2021;Kinsler-Fedon et al, 2020). We previously demonstrated the growth of a six-component aluminum garnet (Lu 1/6 Y 1/6 Ho 1/6 -Dy 1/6 Tb 1/6 Gd 1/6 ) 3 Al 5 O 12 that melted congruently, formed a single phase, and was grown with excellent optical quality and reproducibility (Pianassola, Loveday, Chakoumakos et al, 2020).…”

“…Due to the small size of the dodecahedral site, only Gd 3+ and REs smaller than Gd 3+ form thermodynamically stable single-RE garnets (Wu & Pelton, 1992). For the same reason, smaller REs are preferentially incorporated in multicomponent crystals grown from the melt (Pianassola, Loveday, Chakoumakos et al, 2020). Smaller REs also form congruently melting garnets, while larger Tb 3+ and Gd 3+ form garnets that melt incongruently.…”