Charge‐Induced Disorder Controls the Thermal Conductivity of Entropy‐Stabilized Oxides

Abstract

Manipulating a crystalline material's configurational entropy through the introduction of unique atomic species can produce novel materials with desirable mechanical and electrical properties. From a thermal transport perspective, large differences between elemental properties such as mass and interatomic force can reduce the rate at which phonons carry heat and thus reduce the thermal conductivity. Recent advances in materials synthesis are enabling the fabrication of entropy-stabilized ceramics, opening the door for understanding the implications of extreme disorder on thermal transport. Measuring the structural, mechanical, and thermal properties of single-crystal entropy-stabilized oxides, it is shown that local ionic charge disorder can effectively reduce thermal conductivity without compromising mechanical stiffness. These materials demonstrate similar thermal conductivities to their amorphous counterparts, in agreement with the theoretical minimum limit, resulting in this class of material possessing the highest ratio of elastic modulus to thermal conductivity of any isotropic crystal. CeramicsHigh-entropy alloys (HEAs), consisting of five or more approximately equimolar compositions of elements, [1,2] have proven to exhibit unique physical properties such as high hardness, [3] thermal stability, [4] structural stability, [5] as well as corrosion, oxidation, and wear resistance. [6][7][8] While microstructure and mechanical properties have been extensively studied, thermal

Advanced Materials for High‐Temperature Thermal Transport

“…Braun et al studied their thermal conductivities of a series of high entropy oxides with a single‐phase rocksalt structure carefully. Six different types of ESOs were fabricated, including the five‐cation (Mg 0.2 Ni 0.2 Cu 0.2 Co 0.2 Zn 0.2 )O, and the six‐cation (Mg 1/6 Ni 1/6 Cu 1/6 Co 1/6 Zn 1/6 X 1/6 )O where X = Sc, Sb, Sn, Cr, or Ge.…”

“…a) Κ‐elastic modulus map showing the superior performance of ESOs. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

Solid‐state synthesis of multicomponent equiatomic rare‐earth oxides

“…Recently the high-entropy concept has been extended to metal diborides 17 carbides 18 nitrides, 19 and oxides. 20 The field of high-entropy oxides attracts attention as a current research topic, [21][22][23][24][25][26] particularly due to the functional properties that have been reported, such as high dielectric constant, 27 lithium superionic conductivity, 28 magnetic properties, [29][30][31] electrical and thermal conductivities, 32,33 reversible energy storage, 34 and high catalytic activity in CO oxidation. 35 Launching the field of high-entropy oxides, Rost 20 reported a single rocksalt structure for (Mg ,Ni, Co, Cu, Zn)O pellets produced using solid-state synthesis.…”

A step forward from high-entropy ceramics to compositionally complex ceramics: a new perspective

“…Efforts are being made to extend and validate the descriptor for a broad range of other material systems. Additionally, modeling has revealed the importance of size and interatomic force constant disorder resulting in thermally-insulative HECs [78,[108][109][110]. Various other modeling studies have been conducted [60,[111][112][113][114][115].…”

“…This enables HECs to possess a new unique property since Young's modulus and thermal conductivity are typically inversely correlated, as shown in Fig. 3 (replotted after Braun et al [78]). In Fig.…”