Microstructural regulation and properties enhancement of MgO-CaO ceramics by doping Y_(2)O_(3)

MgO-CaO ceramics with enhanced microhardness and hydration resistance were successfully prepared by doping Y_(2)O_(3) in this work.The effects of introducing Y_(2)O_(3) on the microstructure and properties of MgO-CaO ceramics were investigated.The microstructural regulation effects of Y_(2)O_(3) additive on MgO,CaO,and MgO-CaO ceramics were analyzed comparatively.The results show that Y_(2)O_(3) dissolves into the CaO lattice to form solid solution in CaO ceramics,and no obvious intergranular phase forms.While the Y_(2)O_(3) additive leads to the micro structural reconstruction in MgO and MgO-CaO ceramics.By adding Y_(2)O_(3),SiO_(2) impurity from magnesium source reacts with CaO to form the silicate phases containing Y^(3+)ions in MgO-CaO ceramics.The increase in the MgO/CaO interface and the microstructural reconstruction synergistically improves the microhardness and hydration resistance of MgO-CaO ceramics markedly.

Structural Engineering of Anode Materials for Low-Temperature Lithium-Ion Batteries:Mechanisms,Strategies,and Prospects

The severe degradation of electrochemical performance for lithium-ion batteries(LIBs)at low temperatures poses a significant challenge to their practical applications.Consequently,extensive efforts have been contributed to explore novel anode materials with high electronic conductivity and rapid Li^(+)diffusion kinetics for achieving favorable low-temperature performance of LIBs.Herein,we try to review the recent reports on the synthesis and characterizations of low-temperature anode materials.First,we summarize the underlying mechanisms responsible for the performance degradation of anode materials at subzero temperatures.Second,detailed discussions concerning the key pathways(boosting electronic conductivity,enhancing Li^(+)diffusion kinetics,and inhibiting lithium dendrite)for improving the low-temperature performance of anode materials are presented.Third,several commonly used low-temperature anode materials are briefly introduced.Fourth,recent progress in the engineering of these low-temperature anode materials is summarized in terms of structural design,morphology control,surface&interface modifications,and multiphase materials.Finally,the challenges that remain to be solved in the field of low-temperature anode materials are discussed.This review was organized to offer valuable insights and guidance for next-generation LIBs with excellent low-temperature electrochemical performance.

Dielectric loss enhancement induced by the microstructure of CoFe_(2)O_(4) foam to realize broadband electromagnetic wave absorption

CoFe_(2)O_(4)has been widely used for electromagnetic wave absorption owing to its high Snoek limit,high anisotropy,and suitable saturation magnetization;however,its inherent shortcomings,including low dielectric loss,high density,and magnetic agglomeration,limit its application as an ideal absorbent.This study investigated a microstructure regulation strategy to mitigate the inherent disadvantages of pristine CoFe_(2)O_(4)synthesized via a sol–gel auto-combustion method.A series of CoFe_(2)O_(4)foams(S0.5,S1.0,and S1.5,corresponding to foams with citric acid(CA)-to-Fe(NO_(3))_(3)·9H_(2)O molar ratios of 0.5,1.0,and 1.5,respectively)with two-dimensional(2D)curved surfaces were obtained through the adjustment of CA-to-Fe^(3+)ratio,and the electromagnetic parameters were adjusted through morphology regulation.Owing to the appropriate impedance matching and conductance loss provided by moderate complex permittivity,the effective absorption bandwidth(EAB)of S0.5 was as high as 7.3 GHz,exceeding those of most CoFe_(2)O_(4)-based absorbents.Moreover,the EAB of S1.5 reached 5.0 GHz(8.9–13.9 GHz),covering most of the X band,owing to the intense polarization provided by lattice defects and the heterogeneous interface.The three-dimensional(3D)foam structure circumvented the high density and magnetic agglomeration issues of CoFe_(2)O_(4)nanoparticles,and the good conductivity of 2D curved surfaces could effectively elevate the complex permittivity to ameliorate the dielectric loss of pure CoFe_(2)O_(4).This study provides a novel idea for the theoretical design and practical production of lightweight and broadband pure ferrites.

Microstructure regulation and failure mechanism study of BaTiO_(3)-based dielectrics for MLCC application

Most widely used dielectrics for MLCC are based on BaTiO_(3) composition which inevitably shows performance degradation during the application due to the migration of oxygen vacancies(V_(O)¨).Here,the BaTiO_(3),(Ba_(0.97)Ca_(0.03))TiO_(3),Ba(Ti_(0.98)Mg_(0.02))O_(3),(Ba_(0.97)Ca_(0.03))(Ti_(0.98)Mg_(0.02))O_(3),(Ba0.96Ca_(0.03)Dy0.01)(Ti_(0.98)Mg_(0.02))O_(3) ceramics(denoted as BT,BCT,BTM,BCTM and BCDTM,respectively)were prepared by a solid-state reaction method.The core-shell structured grains(~200 nm)featured with 10-20 nm wide shell were observed and contributed to the relatively flat dielectric constant-temperature spectra of BTM,BCTM and BCDTM ceramics.The TSDC study found that the single/mix doping of Ca^(2+),especially the Mg^(2+),Mg^(2+)/Ca^(2+)and Mg^(2+)/Ca^(2+)/Dy^(3+)could limit the emergence of V_(O)¨during the sintering and suppress its long-range migration under the electric-field.Because of this,the highly accelerated lifetimes of the ceramics were increased and the value of BCDTM is 377 times higher than that of BT ceramics.The p-n junction model was built to explain the correlation mechanism between the long-range migration of V_(O)¨and the significantly increased leakage current of BT-based dielectrics in the late stage of HALT.

Decoupling of thermoelectric transport performance of Ag doped and Se alloyed tellurium induced by carrier mobility compensation

Alloying with Se is proved to be feasible to suppress the lattice thermal conductivity(κL)of tellurium by introducing multidimensional lattice defects.However,extra ionization impurity centers induced by Se alloying are harmful to the electric transport properties of the matrix.In this paper,we propose that the incorporation of Ag could successfully compensate the lost carrier mobility(μH)due to Se alloying through the regulation of microstructure,resulting in the higher power factor(PF)than that of samples without Ag.After composition optimization,theκLdecreased from 1.29 W m^(-1)K^(-1) of Te_(0.99)Sb_(0.01) to 1.05 W m^(-1)K^(-1) of Te_(0.94)Ag_(0.02)Se_(0.03)Sb_(0.01) at 350 K,while the PF remained unchanged or even slightly increased.Benefit from the synergistic effect of carrier mobility compensation and phonon scattering,a maximum z T of 0.91 at 573 K and an average z T of 0.57(between 298 and 573 K)are achieved in Te_(0.94)Ag_(0.02)Se_(0.03)Sb_(0.01).This work presents a new strategy for decoupling the thermal and electric parameters of Te-based thermoelectric materials.