How high is the entropy in high entropy ceramics?

Jochen M Schneider

doi:10.1063/5.0062523

Abstract

In this Perspective, I raise the question whether the terms high entropy ceramics, high entropy nitrides, high entropy oxides, high entropy borides, etc., are meaningful considering the magnitude of the calculated configurational entropy. Here, the origin of Boltzmann's equation is reviewed and the implications for application are discussed. This back to the roots’ excursion may be helpful for approaching an answer to the question raised in the title and for re-evaluating literature reports connecting superior performance with configurational entropy of so-called high entropy ceramics.

Highlights

The lower limit of five elements is imposed because it is considered to be the point, at which the mixing entropy is high enough to counterbalance the mixing enthalpy in most alloy systems and ensures the formation of solid solution phases,” where the abbreviation HEAs stands for high entropy alloys
In this Perspective, I raise the question whether the terms high entropy ceramics, high entropy nitrides, high entropy oxides, high entropy borides, etc., are meaningful considering the magnitude of the calculated configurational entropy
The term “superhard” is frequently applied to materials exhibiting a hardness value of >40 GPa, this definition is arbitrary in the sense that a certain number was selected but not—as in the case of high entropy alloys—that a threshold configurational entropy magnitude is calculated with scitation.org/journal/jap

Summary

Introduction

The lower limit of five elements is imposed because it is considered to be the point, at which the mixing entropy is high enough to counterbalance the mixing enthalpy in most alloy systems and ensures the formation of solid solution phases,” where the abbreviation HEAs stands for high entropy alloys. In this Perspective, I raise the question whether the terms high entropy ceramics, high entropy nitrides, high entropy oxides, high entropy borides, etc., are meaningful considering the magnitude of the calculated configurational entropy.

Results

Conclusion