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

The magnetocaloric (MC) responses of various rare-earth (RE)-dominated magnetic solids have been extensively investigated recently to develop high-performing MC materials for cryogenic cooling applications. Herein, we fabricated a family of single-phase RE-dominated magnetic ceramics, RE₃NbO₇ (RE = Gd, Dy, Ho, and Er), via solid-state reactions and determined their structural and magnetic properties, specifically their cryogenic MC responses, through experiments and theoretical calculations. The prepared RE₃NbO₇ ceramics all crystallize in the orthorhombic weberite-type structure (space group C222₁, No. 20). The constituent elements are uniformly distributed in the RE₃NbO₇ ceramics and are in RE³⁺, Nb⁵⁺, and O²⁻ valence states. All the prepared RE₃NbO₇ ceramics showed considerable cryogenic MC responses, identified by maximum magnetic entropy/temperature-averaged magnetic entropy changes and relative cooling power. Specifically, these MC parameters (ΔH = 0–7 T) comprised 33.76/30.57 J/(kg K) and 362.23 J/kg for Gd₃NbO₇, 19.39/18.72 J/(kg K) and 444.39 J/kg for Dy₃NbO₇, 18.52/18.20 J/(kg K) and 495.9 J/kg for Ho₃NbO₇, and 20.26/19.31 J/(kg K) and 345.45 J/kg for Er₃NbO₇, respectively. These values are superior to those of RE₃RuO₇ ceramics and comparable with those of recently reported RE-dominated MC materials featuring notable MC responses, indicating the promising potential of the RE₃NbO₇ ceramics for cooling applications.