The Third-Order Nonlinear Optical Properties in Cobalt-Doped ZnO Films

We quantitatively investigate the third-order optical nonlinear response of Co-doped ZnO thin films prepared by magnetron sputtering using the Z-scan method. The two-photon absorption and optical Kerr effect are revealed to contribute to the third-order nonlinear response of the Co-doped ZnO films. The nonlinear absorption coefficient β is determined to be approximately 8.8 × 10-5 cm/W and the third-order nonlinear susceptibility X（3） is 2.93 × 10-6 esu. The defect-associated energy levels within the band gap are suggested to be responsible for the enhanced nonlinear response observed in Co-doped ZnO films.

Cobalt-doped TiO_(2)@C hierarchical nanocomposites derived from Ti_(3)C_(2) MXene as cathodes for hybrid magnesium-lithium batteries

TiO_(2)has been explored in hybrid magnesium-lithium batteries(HMLBs)due to the advantages of low self-discharge and small volume expansion during ion insertion.However,how to improve the inherently low ionic and electrical conductivity of TiO_(2)is the problem that needs to be solved.In this work,a smart strategy is adopted to prepare cobalt-doped TiO_(2)@C(Co^(4+)-TiO_(2)@C)hierarchical nanocomposite derived from Co(II)(OH)n@Ti3C2.Compared with TiO_(2)@C(without cobalt doping),Co^(4+)-TiO_(2)@C shows the highest specific capacity(154.7 mAh·g^(-1)at 0.1 A·g^(-1)after 200 cycles)and extraordinary rate performance in HMLBs.The excellent electrochemical performance of Co4+-TiO_(2)@C is ascribed to the synergistic effect of the hierarchical structure and cobalt-doping.Both experimental results and density functional theory(DFT)calculation reveal that the cobalt-doping has effectively improved the electronic conductivity and reduced the Li+migration barrier.This work provides a new insight to design TiO_(2)-based cathode materials with high-performance in HMLBs.

Effect of cobalt on the magnetoresistance characteristics of rare-earth doped manganites

The effect of cobalt-doping on the magnetic,transport and magnetoresistance characteristics of La1-xSrxMnO3 was investigated.The results show that the magnetoelectric property of rare-earth doped manganites is greatly affected by substitution of Co for Mn sites.The Curie temperature as well as the magnetic moment decreases with the increase of doping concentration,and the samples exhibit obvious characteristics of the spin glass state.Moreover,the magnetoresistance is evidently modulated by doping concentration,and the relevant temperature dependence is also suppressed.In addition,low-temperature magnetoresistance is significantly promoted as doping concentration increases,which renders a value of approximately 50% in the temperature range of 5-200 K and varies within 12.5%.It can be attributed to the effect of spin scattering, induced by cobalt doping,on the itinerant electrons of Mn ions,thus introducing a spin-disorder region into the ferromagnetic region of double-exchange interaction between neighbouring Mn^3＋ and Mn^4＋ ions.

Designing Electrochemical Nanoreactors to Accelerate Li_(2)S_(1/2) Three-Dimensional Growth Process and Generating More Li_(2)S for Advanced Li–S Batteries

With advantages of low costs and high energy density,Li–S batteries are considered as one of the most promising energy storage devices.However,Li_(2)S_(2) with a high dissociation energy and insulative properties is hard to convert into Li_(2)S,resulting in underutilization of sulfur capacity.Herein,Co-Mo_(2)C@C yolk–shell spheres as nanoreactors were designed to confront this challenge rationally.The Co-Mo_(2)C@C-induced Li_(2)S_(1/2) nucleation and growth in the three-dimensional process and the cathode produced more Li_(2)S after full discharge.Experimental studies and theoretical calculations reveal that the conversion barrier from Li_(2)S_(2) into Li_(2)S was lowered while the diffusion of lithium ions and electron transfer accelerated when using the Co-Mo_(2)C@C catalyst.Based on the above advantages,the Co-Mo_(2)C@C/S cathode exhibits a high reversible capacity and excellent cyclic stability,such as an initial specific capacity of 1200 mAh g^(−1) at 0.1 C with 709 mAh g^(−1) at 1.0 C after 1000 cycles with a low capacity fading rate of 0.04%per cycle.Even at high densities of 3.0 C and 5.0 C,the specific capacities are 647.6 and 557.7 mAh g^(−1) after 400 cycles,respectively.Impressively,it also shows ca.770 and 900 mAh g^(−1) at 0.2 C after 50 cycles with high sulfur loadings of 4.2 and 5.1 mg cm−2,respectively.The present work may provide new insights into the design of nanoreactors to promote Li_(2)S_(1/2) growth in a three-dimensional process and accelerate conversion from solid Li_(2)S_(2) to solid Li_(2)S in high performance Li–S batteries.

Co-doped IT-M0S2 nanosheets embedded in N,S-doped carbon nanobowls for high-rate and ultra-stable sodium-ion batteries

Despite various 2H-MoS/carbon hybrid nanostructures have been constructed and committed to improve the performance for sodium-ion batteries(SIBs),they still show the limited cycle stability due to the relatively large volumetric expansion during the charge-discharge process Herein,we report the construction of cobalt-doped few-layered 1T-MoS2 nanosheets embedded in N,S-doped carbon(CMS/NSC)nanobowls derived from metal-organic framework(MOF)precursor via a simple in situ sulfurization process.This unique hierarchical structure enables the uniformly dispersed Co-doped 1T-MoS2 nanosheets intimately couple with the highly conductive carbon nanobowls,thus efficiently preventing the aggregation.In particular,the Co-doping plays a crucial role in maintaining the integrity of structure for MoS2 during cycling tests,confirmed by first-principles calculations.Compared with pristine MoS2,the volume deformation of Co-doped MoS2 can be shrunk by a prominent value of 52%during cycling.Furthermore,the few-layered MoS2 nanosheets with 1T metalic phase endow higher conductivity,and thus can surpass its counterpart 2H semiconducting phase in battery performance.By virtue of the synergistic effect of stable structure,appropriate doping and high conductivity,the resulting CMS/NSC hybrid shows superior rate capability and cycle stability.The capacity of CMS/NSC can still be 235.9 mAh·g^-1 even at 25 A·g^-1,which is 51.3%of the capacity at 0.2 A·g^-1.Moreover,the capacity can still remain 218.6 mAh·g^-1 even over 8,240 cycles at 5 Ag·g^-1 with a low decay of 0.0044%per cycle,one of the best performances among the reportec MoS2-based anode materials for SIBs.