Rapid Sol-Gel Synthesis Approach for the Preparation of the Magnetocaloric Antiperovskite Mn₃GaC

Magnetocaloric materials form highly promising candidates to fundamentally change the current vapor compression-based refrigeration technology, with the benefits of bypassing the use of greenhouse gas emissions and improving the energy efficiency. One member within this group of materials is the antiperovskite phase Mn₃GaC. However, despite the big potential that lies in its materials properties, the synthesis of this phase and antiperovskites in general is still mainly achieved by conventional energy-consuming solid-state methods, resulting in long reaction times (>7 days) and challenges in influencing the microstructure or morphology. Here, we report a rapid sol-gel approach using citric acid as a gelling agent, which allows us to obtain a highly phase-pure, crystalline Mn₃GaC phase after only 5 h of annealing. Ex situ X-ray powder diffraction data, combined with DSC/TGA measurements, elucidate the reaction mechanism, which involves carbothermal reduction of intermediate oxides. Vibrating sample magnetometry of the annealed products demonstrates the ability to alternate the magnetic properties of Mn₃GaC simply based on the variation of the gelling agent amount in the reaction mixture. Overall, this offers a facile alternative and energy- and time-efficient approach for the synthesis of antiperovskite carbide phases with the power to specifically influence materials properties by only slight adjustments of parameters within this wet chemical-based synthesis procedure.