Conventional, microwave and spark plasma sintering of high entropy rare earth ceramic: La2O3-CeO2-Pr6O11-Nd2O3

Abstract

In this research, a high-entropy rare-earth oxide (HEO) ceramic with the composition La₂O₃-CeO₂-Pr₆O₁₁-Nd₂O₃ was successfully synthesized via three distinct sintering techniques: conventional, microwave, and spark plasma sintering (SPS). The phase composition, surface chemistry, and microstructural evolution of the resulting materials were systematically characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results demonstrate that the sintering method intensely influences the final produced high entropy. XRD analysis confirmed the formation of a dominant single-phase cubic fluorite structure (Fm-3m) in all samples, with the microwave-sintered sample exhibiting the highest phase purity and crystallinity. While, SPS and conventional sintering led to minor secondary phases and broader diffraction peaks, indicative of finer crystallites and lattice strain. Electron microscopy revealed that SPS produced a highly dense, fine-grained microstructure with superior homogeneity and the lowest porosity, whereas conventional sintering resulted in a porous, irregular morphology. XPS confirmed the presence of the constituent rare-earth elements primarily in their + 3 oxidation state, successfully integrated into the crystal lattice. This study concludes that while microwave sintering is optimal for achieving high phase purity, SPS is the most effective method for producing dense, homogeneous high-entropy rare-earth ceramics with enhanced microstructural properties for advanced applications. © 2025 Elsevier B.V.