Significantly improved near-field communication antennas based on novel Ho^(3+)and Co^(2+)ions co-doped Ni-Zn ferrites

In near-field communication(NFC)antennas,soft magnetic ferrites are usually applied as a substrate to reduce eddy current loss and increase magnetic field coupling.For this purpose,the applied ferrites are required to have high permeability and saturation magnetization together with low magnetic loss and dielectric loss.However,for most soft magnetic ferrites,it is difficult to meet all the requirements.Herein novel Ni-Zn ferrite ceramics co-doped by Ho^(3+)and Co^(2+)ions with chemical formula Ni_(0.5-x)Zn_(0.5)Ho_(0.02)Co_(x)Fe_(1.98)O_(4)(x=0-0.2)were designed and prepared to balance these needs on the basis of molten salt synthesis with metal nitrates as raw materials and potassium hydroxide(KOH)as the precipitation agent and molten salt precursor.After the substitution of Ho^(3+),the saturation magnetization and initial permeability decrease,but with further doping of Co^(2+),the saturation magnetization gradually increases,while the initial permeability continues to decrease.When x=0.1,the sample will have the lowest dielectric constant,magnetic and dielectric loss,as well as the highest Curie temperature(305℃).Moreover,the acquired Ni-Zn ferrites have been applied simulatively in NFC antennas,revealing that the device manufactured with the optimal Ni_(0.4)Zn_(0.5)Ho_(0.02)Co_(0.1)Fe_(1.98)O_(4)ferrite ceramics would have significantly improved performance at 13.56 MHz with low leakage and long transmit distance of magnetic field.Therefore,the Ni_(0.4)Zn_(0.5)Ho_(0.02)Co_(0.1)Fe_(1.98)O_(4)ferrite ceramics would be a good candidate for NFC antenna substrates.

Zn_(0.5)Co_(0.5)Mn_(0.5)Fe_(0.5)Al_(0.5)Mg_(0.5)O_(4) high-entropy oxide with high capacity and ultra-long life for Li-ion battery anodes

Owing to the robust Li-ion storage properties induced by entropy stabilization effect,transition metal(TM)-based high-entropy oxides(HEOs)are promising electrode materials for highperformance Li-ion batteries(LIBs).In this study,a six-component Zn_(0.5)Co_(0.5)Mn_(0.5)Fe_(0.5)Al_(0.5)Mg_(0.5)O_(4) spinel-structured HEO(denoted as 6M-HEO,where M=Zn,Co,Mn,Fe,Al,and Mg)was synthesized using a facile coprecipitation method.When used as an anode of the LIBs,its stable high-entropy nanostructures exhibit high specific capacity(290 mAh·g^(−1) at a current density of 2 A·g^(−1)),ultra-long cycling stability(maintained 81%of the initial capacity after 5000 cycles),and outstanding rate performance.Such excellent performance can be attributed to two factors.Firstly,its high-entropy structure can reduce the stress caused by intercalation and avoid volume expansion of the HEO nanostructures.As a result,the cyclic stability was significantly enhanced.Secondly,owing to the unique element selection in this study,four active elements(Zn,Co,Mn,and Fe)were incorporated in inactive MgO and Al2O3 matrice after the first discharge process,which would allow such high-entropy materials to withstand the rapid shuttle of Li ions.

Progress on rare-earth doped ZnO-based varistor materials

Rare-earth(RE)doping can greatly enhance the voltage gradient of ZnO-based varistors,and their nonlinear coefficient,leakage current,energy absorption capability,through-current capability and residual voltage can also be improved to certain extent.In this review,the progress on RE-doped ZnO-based varistor materials in recent years was summarized.The mechanism of RE doping on the electrical performance of ZnO varistors was analyzed.The issues in exploring new ZnO-based varistor materials by RE doping were indicated,and the development trends in this area were proposed.