Synthesis and characterization of dense, rare-earth based high entropy fluorite thin films

High entropy oxides (HEOs) with 5 or more cations in equimolar proportions that result in a phase-pure material, are a new class of materials attracting a lot of attention in recent years. HEOs exhibit interesting optical, electrochemical, magnetic and catalytic properties. To get a comprehensive understanding of the physics behind the complex interactions taking place in these materials, it is important to evaluate the material in (near-fully) dense forms, such as pellets or thin films. The fluorite structured high entropy oxide, (CeLaSmPrY)O2-x has been investigated only in the powder form and there are no studies on the dense form of fluorite (CeLaSmPrY)O2-x. One of the main reasons is that (CeLaSmPrY)O2-x undergoes a structural transition from fluorite to bixbyite (at 1000 degrees C) and typically temperatures above the transition (> 1200 degrees C) are required for achieving high densities via conventional sintering. In this study, we synthesize dense films of fluorite structured (CeLaSmPrY)O2-x by sol-gel as well as pulsed laser deposition processes. The films synthesized via sol-gel process exhibit equiaxed grains and polycrystalline morphology, whereas columnar and epitaxial films are obtained using pulsed laser deposition. Thus, microstructural tuning of dense fluorite (CeLaSmPrY)O2-x films has been demonstrated while maintaining the basic characteristics of the HEO as observed in the powder form, therefore, paving the way towards more comprehensive studies for possible applications. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).