Temperature coefficients of grain boundary resistance variations in a ZnO/p-Si heterojunction

Heteroepitaxial undoped ZnO films were grown on Si （100） substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃ （Sample 1, S1） and 02-800℃ （Sample 2, S2） for 1 h, respectively. The electrical transport characteristics of a ZnO/p-Si heterojunction were investigated. We found two interesting phenomena. First, the temperature coefficients of grain boundary resistances of S 1 were positive （positive temperature coefficients, PTC） while that of both the as-grown sample and S2 were negative （negative temperature coefficients, NTC）. Second, the I-V properties of S2 were similar to those common p-n junctions while that of both the as-grown sample and S 1 had double Schottky barrier behaviors, which were in contradiction with the ideal p-n heterojunction model. Combined with the deep level transient spectra results, this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO/p-Si heterojunction varied with the different annealing ambiences, which caused the grain boundary barriers in ZnO/p-Si heterojunction to vary. This resulted in adjustment electrical properties ofZnO/p-Si heterojunction that may be suitable in various applications.

Dependence of corrosion resistance on grain boundary characteristics in a high nitrogen CrMn austenitic stainless steel

Processing schedules for grain boundary engineering involving different types of cold deformation（tension, compression, and rolling） and annealing were designed and carried out for 18Mn18Cr0.6N high nitrogen austenitic stainless steel. The grain boundary characteristic distribution was obtained and characterized by electron backscatter diffraction（EBSD） analysis. The corrosion resistance of the specimens with different grain boundary characteristic distribution was examined by using potentiodynamic polarization test. The corrosion behavior of different types of boundaries after sensitization was also studied.The fraction of low-∑ boundaries decreased with increasing strain, and it was insensitive to the type of cold deformation when the engineering strain was lower than 20%. At the strain of 30%, the largest and smallest fractions of low-∑ boundaries were achieved in cold-tensioned and rolled specimens, respectively. The fraction of low-∑ boundaries increased exponentially with the increase of grain size. The proportion of low-∑ angle grain boundaries increased with decreasing grain size. Increasing the fraction of low-∑ boundaries could improve the pitting corrosion resistance for the steels with the same grain size.After sensitization, the relative corrosion resistances of low-∑ angle grain boundaries, ∑3 boundaries, and ∑9 boundaries were 100%, 95%, and 25%, respectively, while ∑27 boundaries, other low-∑ boundaries and random high-angle grain boundaries had no resistance to corrosion.

NASICONs-type solid-state electrolytes:The history,physicochemical properties,and challenges

Solid-state electrolytes are critical for the development of next-generation high-energy and high-safety rechargeable batteries.Among all the candidates,sodium(Na)superionic conductors(NASICONs)are highly promising because of their evident advantages in high ionic conductivity and high chemical/electrochemical stability.The concept of NASICONs was proposed by Hong and Goodenough et al.in 1976 by reporting the synthesis and characterization of Na1+xZr2(SixP3−x)O12(0≤x≤3),which has attracted tremendous attention on the NASICONs-type solid-state electrolytes.In this review,we are committed to describing the development history of NASICONs-type solid-state electrolytes and elucidating the contribution of Goodenough as a tribute to him.We summarize the correlations and differences between lithium-based and sodium-based NASICONs electrolytes,such as their preparation methods,structures,ionic conductivities,and the mechanisms of ion transportation.Critical challenges of NASICONs-structured electrolytes are discussed,and several research directions are proposed to tackle the obstacles toward practical applications.

Halide-based solid electrolytes:The history,progress,and challenges

Lithium metal solid-state batteries(LMSBs)have attracted extensive attention over the past decades,due to their fascinating advantages of safety and potential for high energy density.Solid-state electrolytes(SEs)with fast ionic transport and excellent stability are indispensable components in LMSBs.Heretofore,a series of inorganic SEs have been extensively explored,such as sulfide-and oxide-based electrolytes.Unfortunately,they both have difficulty in achieving a satisfactory balance of conductivity and stability,and oxides suffer from a high impedance of grain boundaries,while sulfides encounter poor stability.Halide-based solid electrolytes are gradually emerging as one of the most promising candidates for LMSBs due to their advantages of decent room temperature ionic conductivity(>10^(−3)S cm^(−1)),good compatibility with oxide cathode materials,good chemical stability,and scalability.Herein,research and development of the widely studied metal halide SEs including fluorides,chlorides,bromides,and iodides are reviewed,mainly focusing on the structures and ionic conductivities as well as preparation methods and electrochemical/chemical stabilities.And then,based on typical metal halide solid electrolytes,we emphasize the interface issues(grain boundaries,cathode−electrolyte and electrolyte–anode interfaces)that exist in the corresponding LMSBs and summarize the related work on understanding and engineering these interfaces.Furthermore,the typical(or in situ)characterization tools widely used for solid-state interfaces are reviewed.Finally,a perspective on the future direction for developing high-performance LMSBs based on the halide electrolyte family is put out.

Correlation Between Microstructure and Corrosion Behavior of Two 90Cu10Ni Alloy Tubes

Two kinds of 90Cu10 Ni tubes with different service lives（more than 3 years and only 1 year,respectively）under identical working conditions were studied by an immersion test in a 3.5 wt% NaCl solution and the electron backscattered diffraction（EBSD） technique.The morphology after immersion showed severer corrosion attack at the grain boundaries of the tube with shorter service life compared with the tube with longer service life.The grain boundary characterization distributions（GBCDs） of the two tubes obtained by EBSD revealed more Σ3 boundaries and twins,and larger random boundary meshes in the tube with longer service life.A short immersion test in a modified Livingston＇s solution was conducted to evaluate the tendency to corrosion attack of different types of the grain boundaries.SEM and AFM were used to characterize the corrosion morphologies of the boundaries.A strong correlation between varying depths of corrosion grooves and types of the grain boundaries was obtained.The influence of deviation angle of low Σ boundaries on corrosion resistance of the grain boundaries was also discussed.It is concluded that a special ‘‘grain boundary engineering＇＇（GBE） treatment has been performed on the tube with longer service life.It is proposed that the optimized GBCD is responsible for the better service performance of the tube.