Our recent progress on magnetic entropy change（S） involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and au...Our recent progress on magnetic entropy change（S） involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and austenite exhibit ferromagnetic（FM） behavior but show different magnetic anisotropies,a positive S as large as 4.1 J·kg^-1·K^-1 under a field change of 0-0.9 T was first observed at martensitic transition temperature T M～197 K.Through adjusting the Ni：Mn：Ga ratio to affect valence electron concentration e/a,T M was successfully tuned to room temperature,and a large negative S was observed in a single crystal.The △S attained 18.0 J·kg^-1·K^-1 under a field change of 0-5 T.We also focused on the metamagnetic alloys that show mechanisms different from the conventional ones.It was found that post-annealing in suitable conditions or introducing interstitial H atoms can shift the T M across a wide temperature range while retaining the strong metamagnetic behavior,and hence,retaining large magnetocaloric effect（MCE） and magnetoresistance（MR）.The melt-spun technique can disorder atoms and make the ribbons display a B2 structure,but the metamagnetic behavior,as well as the MCE,becomes weak due to the enhanced saturated magnetization of martensites.We also studied the effect of Fe/Co co-doping in Ni 45（Co1-xFex）5 Mn36.6In13.4 metamagnetic alloys.Introduction of Fe atoms can assist the conversion of the Mn-Mn coupling from antiferromagnetic to ferromagnetic,thus maintaining the strong metamagnetic behavior and large MCE and MR.Furthermore,a small thermal hysteresis but significant magnetic hysteresis was observed around TM in Ni51Mn49-xInx metamagnetic systems,which must be related to different nucleation mechanisms of structural transition under different external perturbations.展开更多
Supercapacitors with good electrochemical performance and flexibility are in great demand.In this paper,the concept of preparing 3D porous carbon monoliths via direct calcination of melamine sponge is presented.This p...Supercapacitors with good electrochemical performance and flexibility are in great demand.In this paper,the concept of preparing 3D porous carbon monoliths via direct calcination of melamine sponge is presented.This preparation method is simple and has good control of the structure.Porous carbon composite nickel-manga nese oxides can be obtained by hydrothermal method followed with calcination.The electrochemical performances were tested and porous carbon monoliths with NiMn oxides exhibited a specific capacitance of 870 F/g in 1 mol/L KOH at a charge/discharge current density of 0.5 A/g and a capacity retention of 89.9% after 5000 times charge and discharge.展开更多
采用溶剂热法制备前驱体,后经350°C热处理,首次合成了空心结构的NiMn_2O_4微球以及不同含量氧化石墨烯包覆的Ni/Mn_3O_4/NiMn_2O_4@RGO复合材料.电化学性能测试表明,复合负极材料中,含25wt%还原氧化石墨烯的材料储钠性能最佳,其在5...采用溶剂热法制备前驱体,后经350°C热处理,首次合成了空心结构的NiMn_2O_4微球以及不同含量氧化石墨烯包覆的Ni/Mn_3O_4/NiMn_2O_4@RGO复合材料.电化学性能测试表明,复合负极材料中,含25wt%还原氧化石墨烯的材料储钠性能最佳,其在50 m A·g^(-1)电流密度下,100次循环后放电比容量保持在187.8 m Ah·g^(-1),且800 m A·g^(-1)电流密度下的可逆容量高达149.9 m Ah·g^(-1),明显优于NiMn_2O_4及其他石墨烯基复合材料.研究指出,复合材料性能的提升得益于空心微球和还原的氧化石墨烯构成的特殊结构,一方面缩短了电子/离子传输距离,缓解了体积效应,另一方面高导电网络有效增强了活性物质利用率.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51271196,11274357,and 51021061)the Key Research Program of the Chinese Academy of Sciences+1 种基金the National Basic Research Program of China (Grant No. 2010CB833102)the Hi-Tech Research and Development Program of China (Grant No. 2011AA03A404)
文摘Our recent progress on magnetic entropy change（S） involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and austenite exhibit ferromagnetic（FM） behavior but show different magnetic anisotropies,a positive S as large as 4.1 J·kg^-1·K^-1 under a field change of 0-0.9 T was first observed at martensitic transition temperature T M～197 K.Through adjusting the Ni：Mn：Ga ratio to affect valence electron concentration e/a,T M was successfully tuned to room temperature,and a large negative S was observed in a single crystal.The △S attained 18.0 J·kg^-1·K^-1 under a field change of 0-5 T.We also focused on the metamagnetic alloys that show mechanisms different from the conventional ones.It was found that post-annealing in suitable conditions or introducing interstitial H atoms can shift the T M across a wide temperature range while retaining the strong metamagnetic behavior,and hence,retaining large magnetocaloric effect（MCE） and magnetoresistance（MR）.The melt-spun technique can disorder atoms and make the ribbons display a B2 structure,but the metamagnetic behavior,as well as the MCE,becomes weak due to the enhanced saturated magnetization of martensites.We also studied the effect of Fe/Co co-doping in Ni 45（Co1-xFex）5 Mn36.6In13.4 metamagnetic alloys.Introduction of Fe atoms can assist the conversion of the Mn-Mn coupling from antiferromagnetic to ferromagnetic,thus maintaining the strong metamagnetic behavior and large MCE and MR.Furthermore,a small thermal hysteresis but significant magnetic hysteresis was observed around TM in Ni51Mn49-xInx metamagnetic systems,which must be related to different nucleation mechanisms of structural transition under different external perturbations.
基金financial support from the National Natural Science Foundation of China(Nos.21576034 and 51908092)the State Education Ministry and Fundamental Research Funds for the Central Universities(Nos.2019CDQYCL042,2019CDXYCL0031,2018CDYJSY0055,2018CDQYCL0027,106112017CDJQJ138802,106112017CDJSK04XK11 and 106112017CDJXSYY0001)the Joint Funds of the National Natural Science Foundation of ChinaGuangdong(No.U1801254)。
文摘Supercapacitors with good electrochemical performance and flexibility are in great demand.In this paper,the concept of preparing 3D porous carbon monoliths via direct calcination of melamine sponge is presented.This preparation method is simple and has good control of the structure.Porous carbon composite nickel-manga nese oxides can be obtained by hydrothermal method followed with calcination.The electrochemical performances were tested and porous carbon monoliths with NiMn oxides exhibited a specific capacitance of 870 F/g in 1 mol/L KOH at a charge/discharge current density of 0.5 A/g and a capacity retention of 89.9% after 5000 times charge and discharge.
基金supported by the National Natural Science Foundation of China (51572194)the national Key Research and Development Program of China (No. 2018YFB0105900)the Tianjin Major Program of New Materials Science and Technology (No. 16ZXCLGX00070)
文摘采用溶剂热法制备前驱体,后经350°C热处理,首次合成了空心结构的NiMn_2O_4微球以及不同含量氧化石墨烯包覆的Ni/Mn_3O_4/NiMn_2O_4@RGO复合材料.电化学性能测试表明,复合负极材料中,含25wt%还原氧化石墨烯的材料储钠性能最佳,其在50 m A·g^(-1)电流密度下,100次循环后放电比容量保持在187.8 m Ah·g^(-1),且800 m A·g^(-1)电流密度下的可逆容量高达149.9 m Ah·g^(-1),明显优于NiMn_2O_4及其他石墨烯基复合材料.研究指出,复合材料性能的提升得益于空心微球和还原的氧化石墨烯构成的特殊结构,一方面缩短了电子/离子传输距离,缓解了体积效应,另一方面高导电网络有效增强了活性物质利用率.
