Structural and magnetic characterization of weberite-type RE3NbO7 (RE = Gd, Dy, Ho, and Er) ceramics with notable cryogenic magnetocaloric responses

• • Gd3NbO7 achieves a maximum magnetic entropy change (−ΔSMmax) of 33.76 J/(kg K) under ΔH = 0–7 T, with a temperature-averaged entropy change (−ΔSMavg) of 30.57 J/(kg K) and relative cooling power (RCP) of 362.23 J/kg. This performance exceeds that of RE3RuO7 ceramics and positions Gd3NbO7 as a competitive candidate for cryogenic magnetic refrigeration, particularly for nitrogen liquefaction (77 K) and hydrogen liquefaction (20 K), where high entropy change translates to compact and efficient cooling systems. • • Ho3NbO7 exhibits the highest RCP of 495.9 J/kg among the series, despite a moderate −ΔSMmax of 18.52 J/(kg K) and −ΔSMavg of 18.20 J/(kg K) under ΔH = 0–7 T. The superior RCP indicates a broader temperature span of the magnetocaloric effect, which is industrially critical for practical regenerative cooling cycles where a wide operating temperature range reduces the number of material stages and system complexity. • • Dy3NbO7 and Er3NbO7 show −ΔSMmax/−ΔSMavg values of 19.39/18.72 J/(kg K) and 20.26/19.31 J/(kg K), respectively, with RCPs of 444.39 J/kg and 345.45 J/kg under ΔH = 0–7 T. These values are comparable to those of recently reported RE-dominated MC materials, such as Gd2CoTiO6 (39.13 J/(kg K) at 0–7 T) and Gd2Ti2O7, demonstrating that the weberite-type RE3NbO7 family offers a tunable platform for optimizing MC performance via RE selection. • • All RE3NbO7 ceramics crystallize in the orthorhombic weberite-type structure (space group C2221, No. 20) with uniform elemental distribution and RE3+, Nb5+, and O2− valence states. The phase purity and structural stability are essential for reproducible magnetocaloric performance, as secondary phases or valence fluctuations can degrade the magnetic entropy change and introduce hysteresis losses, which are detrimental to the cyclic efficiency of magnetic cooling devices.