Use of rare earth borates in magnetic refrigeration materials and preparation method of rare earth borates

A method for preparing a rare earth borate as a magnetic refrigeration material, wherein the rare earth borate is EuB2O4, Eu2B2O5, or EuB4O7;

• wherein a phase transition temperature of the rare earth borate is <2 K;
• when a temperature is 1.3 K and a magnetic field change is in a range of from 0 to 1 T, a maximum magnetic entropy change of the EuB2O4 is ≤19.4 J·kg−1·K−1, and a maximum magnetic entropy change of the EuB4O7 is ≤21.2 J·kg−1·K−1;
• or, when a temperature is 2.6 K and a magnetic field change is in a range of from 0 to 1 T, a maximum magnetic entropy change of the Eu2B2O5 is ≤13.7 J·kg−1·K−1;
• wherein the method comprises following steps:
• S1, weighing and mixing a europium source, a boride and a first portion of a boron powder according to a stoichiometric ratio, then adding a second portion of the boron powder to a resulting mixture so that the boron powder is excessive, and mixing evenly to obtain a mixed powder;
• S2, adding a solvent to the mixed powder obtained in step S1, and mixing evenly to obtain a slurry;
• S3, subjecting the slurry obtained in step S2 to ball-milling and drying to obtain a precursor powder;
• and
• S4, sintering the precursor powder obtained in step S3 to obtain the rare earth borate;
• wherein in step S1, the rare earth borate is EuB2O4, and a molar ratio of the second portion of boron powder to the first portion of boron powder is (0.65-0.75):1;
• or the rare earth borate is Eu2B2O5, and the molar ratio of the second portion of boron powder to the first portion of boron powder is (0.45-0.55):1;
• or the rare earth borate is EuB4O7, and the molar ratio of the second portion of boron powder to the first portion of boron powder is (0.45-0.55):1;
• wherein in step S4, the sintering is performed at a temperature ranging from 850° C. to 950 ° C., and a holding time of the sintering is 5 hours to 10 hours.