Synthesis-Driven Functionality in High-Entropy Materials

Abstract

Since their discovery in 2015, high-entropy oxides have introduced a paradigm shift in materials science, unveiling a class of compounds with exceptional structural and functional versatility. These high-entropy materials (HEMs) offer exciting opportunities as next-generation alternatives to conventional materials, owing to the synergistic interplay of multiple principal elements that results in enhanced stability, tunability, and multifunctionality. Their unique atomic configurations enable the design of materials with high surface areas and abundant active sites for catalysis, mechanically robust structures for energy storage, or tunable band gaps for electronic and optoelectronic devices. However, the vast compositional space of HEMs presents both a challenge and an opportunity. Meaningful property design requires a deep understanding of how synthesis routes influence structure-property relationships. In this review, a comprehensive overview of established and emerging synthesis strategies for HEMs, focusing on how each method affects resulting structural, electronic, electrochemical, and optical characteristics, is provided. Key process parameters that can be tailored to optimize material performance are highlighted. Additionally, the accelerating role of high-throughput synthesis and characterization in navigating the design space of high-entropy systems is discussed. By systematically connecting synthesis, structure, and function, this review aims to guide the rational design of HEMs for energy applications and beyond.

Keywords: electronic applications; energy applications; high‐entropy materials; high‐entropy oxides; synthesis techniques.

Figure 1

Overview of the various synthesis routes, their advantages, and suggested application areas for high entropy materials.

Figure 2

a) Photographs of ground sintered samples comparing the change in color with composition and sintering atmosphere. Reproduced with permission.^{[ 29 ]} Copyright 2020, John Wiley and Sons. b) Nyquist plots of Na_4.9Sm_0.3Y_0.2Gd_0.2La_0.1Al_0.1Zr_0.1Si₄O₁₂ obtained at different sintering temperatures. Reproduced with permission.^{[ 33 ]} Copyright 2023, John Wiley and Sons. c) XRD patterns for (NiMgCuZnCo)O_x synthesized by ball milling for different times. Reproduced with permission.^{[ 34 ]} Copyright 2019, American Chemical Society. d) Rate capabilities of (FeCoNiCrMn)₃O₄ sintered at varying temperatures from 0.05 to 2 A g⁻¹. Reproduced with permission.^{[ 35 ]} Copyright 2020, Elsevier. e) Nyquist plots of Na_4.9Sm_0.3Y_0.2Gd_0.2La_0.1Al_0.1Zr_0.1Si₄O₁₂ obtained at different sintering times. Reproduced with permission.^{[ 33 ]} Copyright 2023, John Wiley and Sons.

Figure 3

Radar charts for solid‐state and mechanochemical synthesis methods.

Figure 4

Schematic illustration of the co‐precipitation synthesis route, highlighting key factors affecting material properties.

Figure 5

a) Microwave‐based synthesis schematic for HEOs. Adapted with permission.^{[ 114 ]} Copyright 2023, Elsevier. b) TEM micrograph of (Mg, Cu, Ni, Co, Zn)O powder calcined at 950 °C. Reproduced with permission.^{[ 103 ]} Copyright 2021, Elsevier. c) XRD patterns and (d) SEM‐EDS mapping of M₃O₄, (c2) Fe₂MO₄, (c3) Co₂MO₄, (c4) Ni₂MO₄, (c5) Cr₂MO₄, and (c6) Mn₂MO₄, with M = CoCrFeMnNi. Reproduced with permission.^{[ 115 ]} Copyright 2023, Elsevier. e) TEM micrograph of (Cr_0.2Mn_0.2Fe_0.2Ni_0.2Zn_0.2)₃O₄. Reproduced with permission.^{[ 109 ]} Copyright 2023, Elsevier.

Figure 6

Schematic illustration of the sol‐gel synthesis route, highlighting key factors affecting material properties.

Figure 7

Schematic illustration of the solution combustion synthesis route, highlighting key factors affecting material properties.

Figure 8

Radar charts for solution‐based synthesis methods.

Figure 9

a) Schematic illustration of the nebulized spray pyrolysis synthesis route. Reproduced with permission.^{[ 216 ]} Copyright 2014, Elsevier. b) Highlighting the key factors affecting material properties.

Figure 10

Radar charts for gas‐phase and aerosol‐based synthesis methods.

Figure 11

Schematic of (a) the principle of pulsed laser deposition and (b) the effect of increasing energy fluence on the 3D island structure of prepared thin films. Reproduced under terms of CC BY 4.0 license.^{[ 265 ]} Copyright 2022, Springer Nature.

Figure 12

Radar charts for thin‐film deposition techniques.

Figure 13

Scheme of a high‐throughput approach for the preparation of HEMs libraries.