Discovery and Single Crystal Growth of High Entropy Pyrochlores

Lucas A. Pressley; Angela Torrejon; W. Adam Phelan; Tyrel M. McQueen

doi:10.1021/acs.inorgchem.0c02479

Discovery and Single Crystal Growth of High Entropy Pyrochlores

Lucas A. Pressley, Angela Torrejon, W. Adam Phelan, Tyrel M. McQueen

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14 Scopus citations

Abstract

A family of high entropy oxides with the formula Mg2Ta3Ln3O14 (Ln = La, Pr, Nd, Sm, Eu, Gd) has been discovered and synthesized. Single crystals, 5 mm OD × 2.5 cm, for Ln = Nd have been grown using the laser optical floating zone technique. Crystal orientations are confirmed by Laue diffraction, and structure solutions were obtained via single crystal X-ray diffraction. The structure is found to be a partially disordered pyrochlore, space group Fd-3m, fractional chemical formula (Mg0.25Nd0.75)2(Mg0.25Ta0.75)2O7. Magnetization measurements indicate ordinary paramagnetic behavior in all compounds down to T = 2 K, except in the Eu variant which possesses Van Vleck paramagnetism. Specific heat measurements for Ln = Nd shows no phase transitions between T = 300 and 2 K. We demonstrate the ability to prepare magnetically disordered materials by substitution of Mg with Ni, Mn, and Co, demonstrating the flexibility of this family in accommodating defects. The stabilization of these compounds could be due to the entropy gain associated with defects, showcasing a "materials by design"approach by using disorder to stabilize novel magnetic and optical materials. Our work also demonstrates the feasibility of preparing high entropy oxides in single crystalline form.

Original language	English
Pages (from-to)	17251-17258
Number of pages	8
Journal	Inorganic Chemistry
Volume	59
Issue number	23
DOIs	https://doi.org/10.1021/acs.inorgchem.0c02479
State	Published - Dec 7 2020
Externally published	Yes

Funding

This work was funded by the Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM), a National Science Foundation Materials Inno- vation Platform (NSF DMR-1539918). Angela Torrejon gratefully acknowledges that research was sponsored by the Army Educational Outreach Program (AEOP) and was accomplished under AEOP Research & Engineering Apprenticeship Program FY20 Site Agreement. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Educational Outreach Program or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. L.A.P. would like to thank Dr. Maxime Siegler for helping with single crystal data collection, Veronica Stewart with assistance in PPMS measurements, and Juan Chamarro, Hector Vivanco, Tanya Berry, and Mekhola Sinha for their helpful conversations relating to heat capacity analysis.

Funders	Funder number
Army Educational Outreach Program
National Science Foundation Materials Inno- vation Platform
National Science Foundation	DMR-1539918

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title = "Discovery and Single Crystal Growth of High Entropy Pyrochlores",

abstract = "A family of high entropy oxides with the formula Mg2Ta3Ln3O14 (Ln = La, Pr, Nd, Sm, Eu, Gd) has been discovered and synthesized. Single crystals, 5 mm OD × 2.5 cm, for Ln = Nd have been grown using the laser optical floating zone technique. Crystal orientations are confirmed by Laue diffraction, and structure solutions were obtained via single crystal X-ray diffraction. The structure is found to be a partially disordered pyrochlore, space group Fd-3m, fractional chemical formula (Mg0.25Nd0.75)2(Mg0.25Ta0.75)2O7. Magnetization measurements indicate ordinary paramagnetic behavior in all compounds down to T = 2 K, except in the Eu variant which possesses Van Vleck paramagnetism. Specific heat measurements for Ln = Nd shows no phase transitions between T = 300 and 2 K. We demonstrate the ability to prepare magnetically disordered materials by substitution of Mg with Ni, Mn, and Co, demonstrating the flexibility of this family in accommodating defects. The stabilization of these compounds could be due to the entropy gain associated with defects, showcasing a {"}materials by design{"}approach by using disorder to stabilize novel magnetic and optical materials. Our work also demonstrates the feasibility of preparing high entropy oxides in single crystalline form.",

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AU - Pressley, Lucas A.

AU - Torrejon, Angela

AU - Phelan, W. Adam

AU - McQueen, Tyrel M.

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AB - A family of high entropy oxides with the formula Mg2Ta3Ln3O14 (Ln = La, Pr, Nd, Sm, Eu, Gd) has been discovered and synthesized. Single crystals, 5 mm OD × 2.5 cm, for Ln = Nd have been grown using the laser optical floating zone technique. Crystal orientations are confirmed by Laue diffraction, and structure solutions were obtained via single crystal X-ray diffraction. The structure is found to be a partially disordered pyrochlore, space group Fd-3m, fractional chemical formula (Mg0.25Nd0.75)2(Mg0.25Ta0.75)2O7. Magnetization measurements indicate ordinary paramagnetic behavior in all compounds down to T = 2 K, except in the Eu variant which possesses Van Vleck paramagnetism. Specific heat measurements for Ln = Nd shows no phase transitions between T = 300 and 2 K. We demonstrate the ability to prepare magnetically disordered materials by substitution of Mg with Ni, Mn, and Co, demonstrating the flexibility of this family in accommodating defects. The stabilization of these compounds could be due to the entropy gain associated with defects, showcasing a "materials by design"approach by using disorder to stabilize novel magnetic and optical materials. Our work also demonstrates the feasibility of preparing high entropy oxides in single crystalline form.

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Discovery and Single Crystal Growth of High Entropy Pyrochlores

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