Influence of nano-mechanical evolution of Ti_(3)AlC_(2) ceramic on the arc erosion resistance of Ag-based composite electrical contact material

Al-containing MAX phase ceramic has demonstrated great potential in the field of high-performance low-voltage electrical contact material.Elucidating the anti-arc erosion mechanism of the MAX phase is crucial for further improving performance,but it is not well-understood.In this study,Ag/Ti_(3)AlC_(2) electrical contact material was synthesized by powder metallurgy and examined by nanoindentation techniques such as constant loading rate indentation,creep testing,and continuous stiffness measurements.Our results indicated a gradual degradation in the nano-mechanical properties of the Ti_(3)AlC_(2) reinforcing phase with increasing arc erosion times,although the rate of this degradation appeared to decelerate over arc erosion times.Specifically,continuous stiffness measurements highlighted the uneven mechanical properties within Ti_(3)AlC_(2),attributing this heterogeneity to the phase’s decomposition.During the early(1-100 times)and intermediate(100-1000 times)stages of arc erosion,the decline in the nano-mechanical properties of Ti_(3)AlC_(2) was primarily ascribed to the decomposition of Ti_(3)AlC_(2) and limited surface oxidation.During the later stage of arc erosion(1000-6200 times),the inner region of Ti_(3)AlC_(2) also sustained arc damage,but a thick oxide layer formed on its surface,enhancing the mechanical properties and overall arc erosion resistance of the Ag/Ti_(3)AlC_(2).

Ag-Pd alloy decorated ZnIn_(2)S_(4) microspheres with optimal Schottky barrier height for boosting visible-light-driven hydrogen evolution

Rapid charge carrier recombination rate and insufficient light harvesting capacity are two dominat-ing drawbacks encountered in zinc indium sulfide(ZnIn_(2)S_(4))for photocatalytic applications.Herein,a chemical reduction method was performed to combine bimetallic Ag-Pd alloy nanoparticles(NPs)with spherical-like ZnIn_(2)S_(4)(ZIS).By optimizing Ag:Pd molar ratio and overall loading amount,the optimal Ag_(0.25)Pd_(0.75)-ZIS sample exhibited a maximum H_(2)evolution rate(125.4μmol/h)under visible light,which was higher than that of ZIS,Ag-ZIS and Pd-ZIS.The loading of Ag NPs contribution to PHE reaction by its plasmonic effect was negligible compared to that of Pd loading(Schottky effect).The apparent quan-tum yield(AQY)values over Ag_(0.25)Pd_(0.75)-ZIS sample could reach up to 18.3%at 400 nm and 15.8%at 420 nm.The enhanced activity for photocatalytic hydrogen evolution(PHE)over Ag_(0.25)Pd_(0.75)-ZIS sample was mainly due to the bimetallic synergistic effect that presented as follows.Firstly,the plasmon hy-bridization by loading Ag-Pd bimetallic alloy can significantly increase light harvesting capacity of ZIS.Secondly,the optimal Schottky barrier height formed between Ag-Pd alloy and ZIS interface was benefi-cial for prolonging electron-hole pair lifetimes,promoting charge carrier separation and thus facilitating PHE efficiency.Density functional theory(DFT)analysis indicated that the adsorption energy of H∗over Pd_(0.75)Ag_(0.25)alloy was very close to zero and thus theoretically possessed the highest activity for H_(2)evo-lution,which is in line with experimental results.Combined theoretical calculation with experimental results,a reasonable photocatalytic mechanism was proposed and verified.

Enhanced conductivity and stability of Co_(0.98)Cu_(x)Mn_(2.02−x)O_(4)ceramics with dual phases and twin structures

Semiconductor materials with heterogeneous interfaces and twin structures generally demonstrate a higher concentration of carriers and better electrical stability.A variety of Cu-doped Co_(0.98)Cu_(x)Mn_(2.02−x)O_(4)(0≤x≤0.5)negative temperature coefficient(NTC)ceramics with dual phases and twin structures were successfully prepared in this study.Rietveld refinement indicates that the content of a cubic spinel phase increases with increasing Cu content.The addition of Cu can promote grain growth and densification.Atomic-level structural characterization reveals the evolution of twin morphology from large lamellae with internal fine lamellae(LIT lamellae)to large lamellae without internal fine lamellae(L lamellae)and the distribution of twin boundary defects.First-principles calculations reveal that the dual phases and twin structures have lower oxygen-vacancy formation energy than those in the case of the pure tetragonal and cubic spinel,thereby enhancing the transmission of carriers.Additionally,the three-dimensional charge-density difference shows that metal ions at the interface lose electrons and dwell in high valence states,thereby enhancing electrical stability of the NTC ceramics.Furthermore,the additional Cu ions engage in electron-exchange interactions with Mn and Co ions,thereby reducing resistivity.In comparison to previous Cu-containing systems,the Co_(0.98)Cu_(x)Mn_(2.02−x)O_(4)series exhibit superior stability(aging value≤2.84%),tunable room-temperature resistivity(ρ),and material constant(B)value(17.5Ω·cm≤ρ≤7325Ω·cm,2836 K≤B≤4315 K).These discoveries lay a foundation for designing and developing new NTC ceramics with ultra-high performance.