Entropy-Stabilized Oxides owning Fluorite Structure obtained by Hydrothermal Treatment

Luca Spiridigliozzi,Domenico Frattini,Raffaele Cioffi,Gianfranco Dell’Agli,Grazia Accardo,Claudio Ferone

doi:10.3390/ma13030558

Abstract

Entropy-Stabilized Oxides (ESO) is a modern class of multicomponent advanced ceramic materials with attractive functional properties. Through a five-component oxide formulation, the configurational entropy is used to drive the phase stabilization over a reversible solid-state transformation from a multiphase to a single-phase state. In this paper, a new transition metal/rare earth entropy-stabilized oxide, with composition Ce0.2Zr0.2Y0.2Gd0.2La0.2O2−δ, was found after several investigations on alternative candidate systems. X-Ray Diffraction (XRD) analyses of calcined powders pointed out different behavior as a function of the composition and a single-phase fluorite structure was obtained after a specific thermal treatment at 1500 °C. Powders presented the absence of agglomeration, so that the sintered specimen exhibited sufficient densification with a small porosity, uniformly distributed in the sample.

Highlights

Since ancient history, materials science strongly influenced our society, and the discovery of new classes of materials creates exciting research opportunities and possible novel technological breakthroughs
Entropy Alloys (HEAs) [1] over non-metallic systems, Rost et al [2] demonstrated the existence of the so-called Entropy Stabilized Oxides (ESOs) by successfully synthesizing a single-phase 5-component oxide, (Mg0.2 Co0.2 Ni0.2 Zn0.2 Cu0.2 )O, with a rock salt structure stabilized by the configurational entropy
The results of the present study demonstrate that the (Ce0.2 Zr0.2 Y0.2 La0.2 Gd0.2 )O1.7 sample can be considered an ESO, and its entropy-driven single-phase stabilization has been tested through a heat treatment at different temperatures and air quenching to room temperature

Summary

Introduction

Materials science strongly influenced our society, and the discovery of new classes of materials creates exciting research opportunities and possible novel technological breakthroughs. Entropy Alloys (HEAs) [1] over non-metallic systems, Rost et al [2] demonstrated the existence of the so-called Entropy Stabilized Oxides (ESOs) by successfully synthesizing a single-phase 5-component oxide, (Mg0.2 Co0.2 Ni0.2 Zn0.2 Cu0.2 )O, with a rock salt structure stabilized by the configurational entropy. To be “entropy-stabilized”, a system must have both high configurational entropy and positive forming heat (+∆H), being the entropy that controls its thermodynamic stability. The reversibility between low-temperature multiphase and high-temperature single phase is a mandatory requirement of entropy-driven stabilization. Even if several researchers interchangeably use the terms High Entropy Oxides (HEOs) and Entropy Stabilized Oxides (ESOs), Materials 2020, 13, 558; doi:10.3390/ma13030558 www.mdpi.com/journal/materials

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