González-Rivas Mario U, Aamlid Solveig S, Rutherford Megan R, Freese Jessica, Sutarto Ronny, Chen Ning, Villalobos-Portillo Edgar E, Castillo-Michel Hiram, Kim Minu, Takagi Hidenori, Green Robert J, Hallas Alannah M
Department of Physics & Astronomy, University of British Columbia, Vancouver V6T 1Z1, British Columbia, Canada.
Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver V6T 1Z4, British Columbia, Canada.
J Am Chem Soc. 2024 Sep 25;146(38):26048-26059. doi: 10.1021/jacs.4c05951. Epub 2024 Sep 10.
The term sample dependence describes the troublesome tendency of nominally equivalent samples to exhibit different physical properties. High entropy oxides (HEOs) are a class of materials where sample dependence has the potential to be particularly profound due to their inherent chemical complexity. In this work, we prepare a spinel HEO of identical nominal composition by five distinct methods, spanning a range of thermodynamic and kinetic conditions: solid state, high pressure, hydrothermal, molten salt, and combustion syntheses. By structurally characterizing these five samples across all length scales with a variety of X-ray methods, we find that while the average structure is unaltered, the samples vary significantly in their local structures and their microstructures. The most profound differences are observed at intermediate length scales, both in terms of crystallite morphology and cation homogeneity. As revealed by X-ray fluorescence microscopy ideal cation homogeneity is achieved only in the case of combustion synthesis. These structural differences in turn significantly alter the observed functional properties, which we demonstrate via characterization of their magnetic response. While ferrimagnetic order is retained across all five samples, the sharpness of the transition, the size of the saturated moment, and the coercivity all show marked variations with synthesis method. We conclude that the chemical flexibility inherent to HEOs is complemented by strong synthesis method dependence, providing another axis along which to optimize these materials for a wide range of applications.
“样品依赖性”这一术语描述了名义上等效的样品呈现出不同物理性质的棘手趋势。高熵氧化物（HEOs）是一类材料，由于其固有的化学复杂性，样品依赖性在这类材料中可能表现得尤为显著。在这项工作中，我们通过五种不同的方法制备了名义组成相同的尖晶石型高熵氧化物，这些方法涵盖了一系列热力学和动力学条件：固态法、高压法、水热法、熔盐法和燃烧合成法。通过使用多种X射线方法在所有长度尺度上对这五个样品进行结构表征，我们发现虽然平均结构未改变，但样品在局部结构和微观结构上存在显著差异。在中间长度尺度上观察到最显著的差异，无论是在微晶形态还是阳离子均匀性方面。如X射线荧光显微镜所揭示的，只有燃烧合成的情况下才能实现理想的阳离子均匀性。这些结构差异进而显著改变了观察到的功能特性，我们通过对其磁响应的表征来证明这一点。虽然所有五个样品都保留了亚铁磁序，但转变的尖锐程度、饱和磁矩的大小和矫顽力都随合成方法呈现出显著变化。我们得出结论，高熵氧化物固有的化学灵活性与强烈的合成方法依赖性相辅相成，为在广泛应用中优化这些材料提供了另一个维度。
