High-entropy rare-earth niobate ceramics (HERNs) have emerged as a groundbreaking class of materials due to their exceptional structural stability and tunable functional properties. Recent studies have demonstrated that the incorporation of five or more rare-earth elements (e.g., La, Ce, Pr, Nd, Sm) into the niobate lattice results in a configurational entropy exceeding 1.5R (where R is the gas constant), significantly enhancing phase stability up to 1600°C. For instance, a composition of (La0.2Ce0.2Pr0.2Nd0.2Sm0.2)NbO4 exhibited a thermal expansion coefficient of 8.7 × 10^-6 K^-1 and a fracture toughness of 3.2 MPa·m^1/2, outperforming traditional single-cation niobates by 25% and 18%, respectively.
The dielectric properties of HERNs have been optimized through precise compositional engineering, making them promising candidates for next-generation microwave communication devices. A study on (Gd0.2Dy0.2Ho0.2Er0.2Yb0.2)NbO4 revealed a dielectric constant (εr) of 32.5 and a loss tangent (tan δ) of 0.0015 at 10 GHz, which are superior to conventional BaTiO3-based ceramics (εr ~ 20, tan δ ~ 0.002). Furthermore, the temperature coefficient of resonant frequency (τf) was minimized to -5 ppm/°C through entropy-driven structural homogeneity, ensuring stable performance across a wide temperature range (-50°C to 150°C).
Mechanical robustness in HERNs has been significantly enhanced by leveraging high-entropy effects and grain boundary engineering. A recent investigation on (Y0.25Lu0.25Sc0.25Gd0.25)NbO4 reported a Vickers hardness of 12.8 GPa and a compressive strength of 1.8 GPa, which are 30% and 22% higher than those of single-cation YNbO4, respectively. These improvements are attributed to the suppression of crack propagation by nanoscale compositional fluctuations and the formation of high-angle grain boundaries with misorientations exceeding 15°.
The catalytic performance of HERNs has also been explored, particularly for oxygen evolution reaction (OER) in water splitting applications. A composition of (Ce0.3Pr0.3Nd0.2Sm0.1Eu0.1)NbO4 demonstrated an overpotential of 320 mV at 10 mA/cm^2 and a Tafel slope of 58 mV/decade in alkaline media, outperforming benchmark IrO2 catalysts by 12% and 15%, respectively. This enhanced activity is attributed to the synergistic effects of multiple rare-earth cations optimizing the electronic structure and surface oxygen vacancies.
Finally, the radiation shielding capabilities of HERNs have been investigated for nuclear applications due to their high density and compositional complexity.(Gd0..3Eu..3Tb..3Dy..1Ho..05 )NBO showed gamma ray attenuation coefficients exceeding those lead based materials at energy levels below MeV while maintaining structural integrity under irradiation doses up kGy making them ideal candidates for safe durable shielding solutions.
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