Synthesis, characterization, and single-crystal growth of a high-entropy rare-earth pyrochlore oxide

Candice Kinsler-Fedon, Qiang Zheng, Qing Huang, Eun Sang Choi, Jiaqiang Yan, Haidong Zhou, David Mandrus, and Veerle Keppens

Phys. Rev. Materials 4, 104411 – Published 19 October 2020

Abstract

The synthesis and single-crystal growth of a rare-earth high-entropy oxide ${({Yb}_{0.2} {Tb}_{0.2} {Gd}_{0.2} {Dy}_{0.2} {Er}_{0.2})}_{2} {Ti}_{2} O_{7}$ in the cubic pyrochlore phase $F d \bar{3} m$ are achieved by solid-state reaction and optical floating-zone growth techniques. X-ray diffraction and a structure refinement analysis confirm a single-phase pyrochlore structure and lattice parameter of $a = 10.1152 (3) Å$ . Additional characterization techniques, including scanning transmission electron microscopy and nanoscale electron-energy loss spectroscopy mapping, support a single-phase pyrochlore structure with a homogeneous mixture down to ∼2.3 nm. Magnetization measurements on a single crystal reveal antiferromagnetic correlations with a spin-glass ground state. These results show that it is possible to grow large single crystals of a high entropy pyrochlore oxide, expanding the avenues for future high-entropy oxide research.

Received 20 May 2020
Accepted 10 September 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.104411

Physics Subject Headings (PhySH)

Antiferromagnetism Crystal growth Frustrated magnetism Magnetic susceptibility Paramagnetism

Pyrochlores Single crystal materials Spin glasses

AC susceptibility measurements DC susceptibility measurements Magnetization measurements Scanning transmission electron microscopy X-ray diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Candice Kinsler-Fedon ^1,*, Qiang Zheng^1,2, Qing Huang³, Eun Sang Choi⁴, Jiaqiang Yan ², Haidong Zhou³, David Mandrus^1,2, and Veerle Keppens ^1,†

¹Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, USA
²Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA
⁴National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA

^*Corresponding author: ckinsle1@vols.utk.edu
^†Corresponding author: vkeppens@utk.edu

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Issue

Vol. 4, Iss. 10 — October 2020

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Images

Figure 1
Room-temperature powder x-ray diffraction pattern of polycrystalline ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ . The refinement pattern (red line) overlays the observed pattern (black circles) which matches the $F d \bar{3} m$ cubic structure (green vertical dashed lines are the Bragg reflections characteristic of the pyrochlore phase). The difference pattern is represented in blue below the diffraction pattern.
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Figure 2
(a) Resulting multicrystal of ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ of 7 cm length. (b)–(d) Laue diffraction patterns of ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ taken from various sections of the ingot showing good quality with (b) aligned in the [111], (c) in the [110], and (d) in the [100].
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Figure 3
Typical HAADF-STEM images along the [011] zone axis for (a) single-crystalline and (b) polycrystalline ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ , respectively. The inset in (a) is the crystal structure in this projection, where only cations are shown (the red and the blue are Ti and rare-earth atoms, respectively). The intensity variations arise from three types of atomic columns along this direction. The columns with brightest, intermediate, and weakest contrasts involve 100% rare-earth atoms, 50% rare-earth atoms plus 50% Ti atoms, and 100% Ti atoms, respectively.
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Figure 4
HAADF-STEM imaging and nanoscale electron-energy loss spectroscopy (EELS) mapping along [001] for the single-crystalline ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ . (a) Atomic-resolution HAADF image for the EELS mapping region with the dimension of 27 × 27 nm. (b)–(g) EELS mapping analysis: (b) HAADF image recorded simultaneously during the EELS data set acquisition; (c) Yb, (d) Tb, (e) Gd, (f) Dy, and (g) Er chemical maps obtained from their $M_{5}$ signals, respectively. Note that each pixel in the EELS maps is scanned by 16 × 16 for the simultaneously recorded HAADF image in (b), resulting in atomic resolution in (b) with nanoscale resolution in the EELS maps in (c)–(g).
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Figure 5
DC susceptibility measurements on ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ polycrystal (a) and single crystal with applied magnetic field along the [100] direction (b) from 3 to 300 K, along with the magnetization curves (c) at 3 K from −7 to 7 T.
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Figure 6
AC susceptibility measurements (the real part) on single crystal ${(5 R E_{0.2})}_{2} {Ti}_{2} O_{7}$ from temperatures of 0.3 to 1.7 K with (a) magnetic fields ranging from 0 to 1 T and (b) dependence on frequency ranging from 47 to 995 Hz, indicating a spin-glass magnetic ground state. (c) Linear relation of frequency dependence to freezing temperature (Vogel-Fulcher law).
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