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.

Tunable W5+ Absorbance in Laser Floating Zone Grown Bismuth Tungstate

“…We see that for Bi 1.887 W 0.934 O 5.622−δ , δ = 0.238. This tunability is seen in other floating zone grown crystals for potential application as high-temperature optical sensors …”

Ho2Pd1.3Ge2.7 – a ternary AlB2-type cluster glass system

“…This might be, however, an important contribution in case of systems that are on the edge of instability. 29,30 The problem of estimation of the effective atomic size is rather complicated in the Ho 2 Pd 1+x Ge 3Àx . Depending on the type of atomic size measure (atomic, covalent, or ionic radius) and the specic way it is estimated, the relative size of Pd with respect to Ge can vary substantially.…”

Crystal growth and phase formation of high‐entropy rare‐earth monoclinic aluminates

“…In this work, we demonstrate crystal growth of high‐entropy RE 4 Al 2 O 9 for the first time, contributing to the emerging field of crystal growth of high‐entropy oxides 24–34 . The phase formation and optical quality of crystals containing five REs, including Lu, Yb, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, and La were evaluated.…”

“…In this work, we demonstrate crystal growth of highentropy RE 4 Al 2 O 9 for the first time, contributing to the emerging field of crystal growth of high-entropy oxides. [24][25][26][27][28][29][30][31][32][33][34] The phase formation and optical quality of crystals containing five REs, including Lu, Yb, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, and La were evaluated. Our composition formulation strategy used the RE 3+ average ionic radius (AIR) as a parameter to evaluate its effects on phase formation and optical quality.…”