| Magnetic refrigeration technology is a kind of based on magnetocaloric effect way of solid-state refrigeration material,compared with the traditional way of gas compression refrigeration with green environmental protection,the advantages of high efficiency and energy saving,is at room temperature in the field of refrigeration and development prospect of a new generation of refrigeration technology.Perovskite manganese oxide due to its stable structure,low cost,high Curie temperature magnetocaloric effect,easy to control advantages of doping elements,has the potential to become a magnetic refrigeration materials,and at the same time caused the wide attention of the researchers.In addition,this kind of material of the rich physical properties such as: orderly charge,orbital,the phenomenon such as phase separation,and its internal existing spin,lattice,the strong coupling between rail and charge,is it an ideal material of condensed matter physics research.This paper through to the perovskite manganese oxide for A and B ion doping,study the structure of different ion doping on the material,the influence of the magnetic and magnetocaloric effect,and the structure of the material change on the influence of the magnetic mechanism for further exploration.The main research contents include:1.Based on La0.65Sr0.35MnO3,the sample of La0.65Sr0.35-x(Gd,Ce,Na)x MnO3(x =0~ 0.3)series was prepared by sol-gel method.The structure was analyzed by X-ray diffraction,and the sample was observed by scanning electron microscope.The magnetic data of the samples was measured by the superconducting quantum interferometer.The study found that the structure of the material changed after doping with different elements,but the phase change type did not change.As the Gd3+ ions and the increase of Na+ ion doping amount,the Curie temperature of corresponding samples are present a downward trend,on the one hand,it is the result after different ions doped crystal cell parameters,cause A site average ionic radius change,leading to the tolerance factor and A-cation radius distribution change.On the other hand,the introduction of different valence ions has changed the ratio of the mixture valence of manganese,thus weakening the exchange function.In doping Na+ ions samples,less large magnetic entropy change after the first increases,when the doping amount of 0.3 x,Curie temperature of 335 K,at this point,the largest magnetic entropy change and the relative maximum cooling efficiency,were 1.12 and 40.3 J/kg K J/kg.In Gd ions doped samples,As the doping amount increases,the lattice distortion of each sample also increases,tolerance factor and degree of mismatch are declining.Curie temperature shows a decreasing trend due to the weakening of the exchange effect.When the doping amount is 0.15,the Curie temperature of the material is 300 K,and the relative cooling capacity reaches 215.76 J/kg,which has a good prospect in the field of room temperature magnetic refrigeration.2.The effect of B-site doping with different transition metal ions on the microstructure,magnetic and magnetocaloric effects in La0.65Ca0.35Mn1-x Nix O3 and La0.65Sr0.25K0.1Mn1-x Vx O3 has been investigated.For the sample of V ion doping,its Curie temperature shows an increasing trend with the increase of doping.For the sample of Ni ions,the maximum magnetic entropy of the sample with x=0.05 is at 2.28 J/kg K,which is 70.15% of metal Gd.Besides,we further analyzed the phase change type and heat capacity of the material,and found that the paramagnetic-ferromagnetic changes that occurred near the Curie temperature were secondary phase transitions. |
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