P-type Semiconductor Characteristics Research Articles

Phase Transitions and Thermoelectric Properties of Charge-Compensated ZnxCu12−xSb4Se13

In this study, we investigated the phase transitions and thermoelectric properties of charge-compensated hakite (ZnxCu12−xSb4Se13) as a function of Zn content. Based on X-ray diffraction and a differential scanning calorimetric phase analysis, secondary phases (permingeatite and bytizite) transformed into hakite depending on the Zn content, while Zn2Cu10Sb4Se13 existed solely as hakite. Nondegenerate semiconductor behavior was observed, exhibiting increasing electrical conductivity with a rising temperature. With an increase in Zn content, the presence of mixed phases of hakite and permingeatite led to enhanced electrical conductivity. However, Zn2Cu10Sb4Se13 with a single hakite phase exhibited the lowest electrical conductivity. The Seebeck coefficient exhibited positive values, indicating that even after charge compensation (electron supply) by Zn, p-type semiconductor characteristics were maintained. With the occurrence of an intrinsic transition within the measured temperature range, the Seebeck coefficient decreased as the temperature increased; at a certain temperature, Zn2Cu10Sb4Se13 exhibited the highest value. Thermal conductivity showed a low temperature dependence, obtaining low values below 0.65 Wm−1K−1. A power factor of 0.22 mWm−1K−2 and dimensionless figure of merit of 0.31 were achieved at 623 K for ZnCu11Sb4Se13.

Anion replacement effect on the structural, magnetoelectronic, and optical features of all inorganic halide double perovskites K2LiMoX6 (X= Br, I) for spintronic and optical devices

Herein, the geometrical, magnetic, optoelectronic, thermoelectric features of K2LiMoX6 (X = Br, I) have been simulated by DFT. The FP-LAPW approach is employed via Wien2k software. To confirm the thermodynamic and structural stability of the K2LiMoX6 (X = Br, I) compounds, the tolerance factor (τ) and formation enthalpy are calculated. The predicted spin-polarized band structure (BS) and density of states (DOS) display p-type semiconductor character via direct band gap at X-X symmetry points in both spin versions. The ferromagnetic (FM) character was confirmed from magnetic moments (MTot) which are 3.00090, and 3.00014 μB for K2LiMoBr6, and K2LiMoI6, correspondingly. The materials light absorbance was observed in the range of visible to ultraviolet (UV) zone, thereby enhancing their significance for photocell and optoelectronic devices. In addition, both halides exhibit optimal figure of merit (ZT) which make these materials as promising candidates for efficient heat energy conversion technologies. The outcomes of the studied compounds provide a new path for researchers for the applications of spintronic and optical gadgets.

Insight into structural, electronic, optoelectronic, dynamic, elastic, thermal and magnetic properties of pure and doped LiMgSb by nitrogen: Ab-initio calculations

In this work, ab-initio simulation has been conducted to explore and compare various properties, structural, electronic, optoelectronic, dynamic, elastic and magnetic of the pure bulk unit cell of LiMgSb and substituted by nitrogen (N). Herein, we have optimized the lattice parameter of the structure using the both approximations, generalized gradient approximation (GGA) and self-interaction correction (SIC), finding values of 6.9 and 6.7 Å, respectively. Additionally, the undoped system exhibits characteristics of a non-magnetic P-type semiconductor. The forbidden band of the compound is an indirect one at Γ-X points, aligning with existing literature, and measuring 0.742 eV and 0.95 eV under the GGA and SIC approximations, respectively. We have also investigated how the bandgap varies with the lattice parameter to analyze the influence of atomic interactions on the electronic band structure. Further analyses include the calculation of the energy photon wavelength and refractive index corresponding to the pure LiMgSb band gap. The electronic and dynamic stabilities of the compound have been confirmed through calculations of formation energies and phonon dispersion and total density of states. The bulk modulus, elastic constants, Debye temperature and melting temperature have been determined, indicating elastic stability of the system. Moreover, substitution doping the compound with N in different antisites positions with various concentrations has revealed ferromagnetic stability in Li1-xNxMgSb and LiMg1-xNxSb. Emphasis has been placed on the half-metallic behavior of the doped alloys, with an estimation of the Curie temperature utilizing mean field theory. Hence, the predicted compounds hold potential for multifaceted applications in spintronics and optoelectronics.

O-B(F)←N Functionalized Copolymers with Delayed Fluorescence and P-Type Semiconducting Characteristics.

Conjugated polymers with integrating properties of delayed fluorescence and photovoltaic responses simultaneously are scarcely reported due to the generally contradictory requirements for molecular structures to achieve the two properties. Herein, an O-B(F)←N functionalized fused unit (M) with multiple resonance features, small energy gap between lowest singlet excited state (S1) and triplet excited state (T1) (ΔEST = 0.23eV), and delayed fluorescence (τD = 0.75 µs), is designed. Selecting three benzodithiophene (BDT) derivatives as co-units to copolymerize with M, leading to a series of O-B(F)←N embedded polymers also maintaining delayed fluorescence (τD = 0.4-0.5 µs). Moreover, p-type semiconductor characteristics are tested for these polymers with hole mobilities in the range of 10-6-10-5 cm2/Vs. Devices with obviously photovoltaic responses are prepared using these polymers as donors and Y6 as the acceptor, affording a preliminary efficiency of 5.05%. This work successfully demonstrates an effective strategy to design conjugated polymers with integrating properties of delayed fluorescence and photovoltaic performance simultaneously by introducing O-B(F)←N functional groups to polymer backbones.

Orietation-controlled synthesis and Raman study of 2D SnTe

Tin telluride (SnTe), as a narrow bandgap semiconductor material, has great potential for developing photodetectors with wide spectra and ultra-fast response. At the same time, it is also an important topological crystal insulator material, with different topological surface states on several common surfaces. Here, we introduce different Sn sources and control the growth of regular SnTe nanosheets along the (100) and (111) planes through the atmospheric pressure chemical vapor deposition method. It has been proven through various characterizations that the synthesized SnTe is a high-quality single crystal. In addition, the angular resolved Raman spectra of SnTe nanosheets grown on different crystal planes are first demonstrated. The experimental results showed that square SnTe nanosheets grown along the (100) plane exhibit in-plane anisotropy. At the same time, we use micro-nanofabrication technology to manufacture SnTe-based field effect transistors and photodetectors to explore their electrical and optoelectronic properties. It has been confirmed that transistors based on grown SnTe nanosheets exhibit p-type semiconductor characteristics and have a high response to infrared light. This work provides a new approach for the controllable synthesis of SnTe and adds new content to the research of SnTe-based infrared detectors.

Novel Porphyrinic Covalent Organic Polymer with Polarity-Switchable Dual Wavelength for Accurate and Sensitive Photoelectrochemical Sensing.

Herein, we synthesized a novel porphyrinic covalent organic polymer (TPAPP-PTCA PCOP) for constructing a polarity-switchable dual-wavelength photoelectrochemical (PEC) biosensor with ferrocene (Fc) and hydrogen peroxide (H2O2) as regulator and amplifier simultaneously. Interestingly, this new PCOP possessed both n-type and p-type semiconductor characteristics, which thus enabled the appearance of a dual-polarity photocurrent at two different excitation wavelengths. Furthermore, Fc and H2O2 could readily switch the photocurrent of PCOP to the cathode and anode stemming from its efficient electron collection and donation function, respectively. Based on these, a PCOP-based PEC biosensor skillfully integrating dual wavelengths with reliable accuracy and polarity switch with high sensitivity was instituted. As a result, the developed PEC biosensor exhibited a low detection limit down to 0.089 pg mL-1 for the most powerful natural carcinogen aflatoxin M1 (AFM1) assay. Impressively, the target exhibited a completely opposite photocurrent difference to the interfering substances, and the linear correlation coefficient of the assay was improved compared to single-wavelength detection. The PEC sensing platform not only provided a basis for exploring multicharacteristic photoactive material but also innovatively developed the detection mode of the PEC biosensor.

Ultra-high photo responsivity and self-powered photodetector in broad spectral range based on non-layered MnSe/WSe2 heterojunction

Due to its good p-type semiconductor characteristics, MnSe has a great application prospect in high-performance electronic and optoelectronic devices. However, heterojunctions of MnSe still need to be deeply studied to improve its electrical and photoelectric properties. Here, it is reported that the two-dimensional (2D) MnSe/WSe2 heterojunction is structured by the non-layered MnSe nanosheets synthesized by chemical vapor deposition (CVD) method and the mechanically exfoliated layered WSe2. The heterojunction device exhibits a rectification effect and a current on/off ratio of 6,557. Meanwhile, it has a broad spectral range response from ultraviolet (UV) to short-wave infrared radiation (SWIR) (300–2,200 nm), and achieves an ultra-high responsivity of 156 A/W, along with an excellent detectivity of 2.21 × 1012 jones, and an outstanding external quantum efficiency (EQE) of 36,400%. Moreover, the type II band alignment and the built-in potential in the MnSe/WSe2 heterojunction can facilitate the separation of the photoexcited electron-hole pairs, which enables the significant photovoltaic characteristics and self-powered photoswitching response. This work reveals the novel performance of the 2D MnSe/WSe2 heterojunction and a great potential in photoswitching, photodetector, and photovoltaic applications.

High-energy composite cathode for solid-state lithium-oxygen battery boosted by ultrafine carbon nanotube catalysts and amorphous lithium peroxide

Rechargeable solid-state lithium-oxygen batteries (SSLOBs) promise high energy density and safety but suffer from the severe interface impedance in composite cathodes and the failure to detect discharge products by spectroscopy and microscopy originating from low actual discharge capacity. Here, an ultrafine carbon nanotube (CNT) is developed as a cathode catalyst for SSLOBs, which unexpectedly improves the solid-solid contact issue with Li1·5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte and provides a superior specific capacity of 5803 mAh/g (100 mA/g, 2.0–5.0 V vs. Li/Li+) in oxygen atmosphere that is about 4–5 times higher than that of SSLOBs using CNTs with large diameters. This phenomenon is attributed to the optimization of the impedance of CNTs@LAGP induced by the enhanced catalytic activity and enlarged specific surface area of ultrafine CNTs. The amorphous discharge products formed on the CNT surface and between the CNTs and LAGP particles are first found to significantly reduce the cell impedance and increase new reactive sites. Moreover, the irreversible disruption and passivation of CNTs and the accumulation of residual discharge products, which are the fundamental sources of capacity degradation, are further discussed. Importantly, Li2O2 growth morphology as a function of discharge depth and the possible conduction paths of amorphous (Li2O2)n cluster with p-type semiconductor characteristics are also determined by computations based on molecular dynamics and density functional theory for the first time. Our results innovatively reveal the controversial association between impedance and microstructure of composite cathodes, and thus, benefit the development of high-efficiency catalysts and the design of high-energy cathode structures for SSLOBs and other potential solid-state batteries.

An atomic/molecular-level strategy for the design of a preferred nitrogen-doped carbon nanotube cathode for Li-O2 batteries

The formation and growth of Li2O2, the primary discharge product with extremely low conductivity, will cause the passivation of the cathode and the failure or even death of Li-O2 batteries. In this paper, by means of molecular dynamics and density functional theory, we systematically investigated the morphology evolution and electron transport pathway of (Li2O2)n on the surface of nitrogen-doped carbon nanotubes (NCNTs) and the effects of the possible N configuration on the growth stability of (Li2O2)n. Our results demonstrated that the morphology of (Li2O2)n on the surface of NCNTs undergos a process from scattered small-sized clusters to film-like (axial) and toroidal (circumferential) large clusters, and finally completely surrounded the NCNTs. Compared with graphitic N1 and graphitic N2, Li2O2 tends to aggregate stably on the surface of pyridinic N3 and pyridinic N4, which can effectively reduce the capacity loss caused by Li2O2 branches and free state Li2O2. In addition, a stable gap exists between Li2O2 and NCNTs, which is attributed to the Coulomb force and van der Waals interaction. Importantly, (Li2O2)n with p-type semiconductor characteristics acts as a bridge between NCNTs, and electrons are mainly transferred along the surface of (Li2O2)n clusters. Moreover, increasing the wall number of NCNTs and using NCNT bundles were found to be beneficial to improving the deposition stability of (Li2O2)n. Notably, pyrrolic N3 with unstable structure is not recommended for practical application. These results offer general guidelines for designing highly active catalysts for Li-O2 batteries in terms of the optimization of the NCNT-based cathode, and the unique research methods also shed more light on the analysis of the discharge product behavior of other potential metal-air batteries.

Phase control of two-dimensional tin sulfide compounds deposited via atomic layer deposition

Two-dimensional (2D) semiconductor materials are emerging as potential candidates for emerging electronic device applications due to their excellent electrical properties and unique properties such as flexibility and transparency. Among the various potential 2D semiconductor materials, tin sulfide compounds can form polymorphs of different 2D crystals: 2D layered-SnS2 with hexagonal symmetry and 2D layered SnS with orthorhombic symmetry. In addition, since they each have different electrical and optical properties, their controlled growth is important for appropriate target applications. Therefore, we investigated the phase control of tin sulfide compounds deposited via atomic layer deposition according to their deposition temperature and post-annealing conditions. A strategy for controlling the growth of SnS2 or SnS was proposed by investigating phase transition tendencies according to deposition temperature and annealing conditions (temperature, pressure, atmosphere). As a result, it was possible to selectively deposit SnS2 and SnS thin films based on a phase transition study; it was confirmed that SnS2 and SnS thin films exhibited n-type and p-type semiconductor characteristics, respectively.

Effect of Nb content on the microstructure and corrosion resistance of FeCoCrNiNbx high-entropy alloys in chloride ion environment

In this paper, FeCoCrNiNbx high-entropy alloys were prepared by vacuum arc melting, and their microstructure and corrosion resistance in a chloride ion environment were investigated. The results indicated that FeCoCrNi alloy was a single FCC solid solution and FeCoCrNiNbx alloy was a duplex alloy with FCC phase and Laves phase. FeCoCrNiNb0.15 showed the best corrosion resistance. The corrosion current density of FeCoCrNiNb0.15 decreased by one order compared with 316LSS, and the corrosion rate after the immersion experiment was only one-third of 316LSS. The P-N junction improved the corrosion resistance of the passive film of FeCoCrNiNb0.15, while the passive film of FeCoCrNi mainly exhibited n-type semiconductor characteristics with less obvious p-type semiconductor characteristics.

Versatile TiO2 bandgap modification with metal, non-metal, noble metal, carbon material, and semiconductor for the photoelectrochemical water splitting and photocatalytic dye degradation performance

TiO2 is a flexible material for photocatalytic applications owing to its convenient redox potential, eco-friendliness, and abundance. However, TiO2 requires minor adjustments to improve its absorption ability and to suppress charge carrier recombination. Hence, simple chemical procedures have been used to modify TiO2 by using metals (e.g., Ni), non-metals (e.g., N), noble metals (e.g., Ag), carbon materials (e.g., carbon nanofibers), and semiconductors (Fe2O3) as dopants or by forming composites. The photoelectrochemical (PEC) water splitting and photocatalytic dye degradation performance of the synthesized materials were compared. Fe2O3-TiO2 composite performed admirably in both reactions owing to its unique absorption strength and the formation of the heterojunction interface. Fe2O3-TiO2 demonstrated azo dye degradation efficiency of 94.4%. The Fe2O3-TiO2 photoelectrode in the PEC system exhibited a photocurrent response of 0.244 amp/cm2. This outstanding performance is due to the formation of the heterojunction interface that is attributable to the p-type and n-type semiconductor characteristics of the composite. Moreover, the noticeable absorption strength of Fe2O3-TiO2 enables the generation of additional charge carriers and effectively reduces the recombination rate owing to the formation of the heterojunction interface. Characterization techniques including X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, fluorescence spectroscopy, scanning electron microscopy, and transmission electron microscopy, were used to investigate the photocatalytic characteristics. This study promotes the development of new heterojunction semiconductors and dopants for photocatalytic applications.

Electrochemical corrosion and passive behavior of a new high-nitrogen austenitic stainless steel in chloride environment

In this work, the electrochemical corrosion and passive behavior of a high-nitrogen austenite stainless steel named QN2109 in different NaCl solutions were studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and X-ray photoelectron spectroscopy (XPS). QN2109 stainless steel exhibited a wide passive region and high impedance value in the chloride environment. The high ratio of O2−/OH− made the passive film better self-repair effect, and the passive film is mainly composed of Mo-oxides, Fe-oxides and Cr-oxides, providing excellent pitting corrosion resistance at room temperature. The passive film with p-type and n-type semiconductor characteristics showed a double-layer structure. In addition, the influence of CrN and NH3/NH4+ in passive films was also discussed.

First-principles study of divacancy defect in arsenene nanoribbon

Based on the density functional theory, we performed first-principles calculations to investigate the effect of divacancy defects on the electronic and optical properties of arsenene nanoribbons (AsNRs). We found that a 585 defect was formed and AsNR with a slanting oriented divacancy is more stable than with a parallel-oriented one, which is mainly because the former is closer to the edge of AsNRs. A divacancy defect decreases the direct band gap of AsNR, and the Fermi level is closer to the valence bands, indicating a p-type semiconductor character. The defect bands mainly originate from the 585 ring and nearby arsenic atoms. The dielectric function of the divacancy defect AsNR in the two polarization directions is slightly smaller than that of the intrinsic AsNR, and its static dielectric function increases. Our calculations provide significant possibilities for the application of AsNRs to optoelectronic devices.

Doping effects on electronic structures and current-voltage characteristics of GR/InSe/GR selectors

The graphene(GR)/InSe/GR selector was designed based on the rectifying effect of the Schottky barrier at the GR/InSe heterostructure interface. The selector performance was improved by doping groups I–VII A elements, and the effects were studied by first-principles calculations. The band structure results showed that InSe retained p-type semiconductor characteristics only when Se atoms were substitutionally doped by groups IV A (C, Si, Ge) and VI A (O, S) elements. The band gap of the GR/InSe heterostructure doped with group IV A (C, Si, Ge) elements became narrower, and the conductivity became stronger. The band structures of the GR/InSe heterostructures doped with group VI A (O, S) elements were hardly changed. From the plane average electrostatic potential and the charge density difference, it is observed that doping of group IV A (C, Si, Ge) elements reduced the height and width of the Schottky barrier at the interface and enhanced the built-in electric field strength of the heterostructures. Finally, the current-voltage (I-V) curves show that compared with the undoped GR/InSe/GR selector, the on-state current (Ion) and nonlinearity (NL) coefficient of selectors doped with group IVA (C, Si, Ge) elements increased, and the threshold voltage (Vth) and off-state current (Ioff) decreased. It can better suppress the influence of the leakage current on the RRAM, which is important for the development of high-performance and low-power selectors.

The effect of boron concentration on the electrical, morphological and optical properties of boron-doped nanocrystalline diamond sheets: Tuning the diamond-on-graphene vertical junction

In this paper, the effect of boron doping on the electrical, morphological and structural properties of free-standing nanocrystalline diamond sheets (thickness ~ 1 μm) was investigated. For this purpose, we used diamond films delaminated from a mirror-polished tantalum substrate following a microwave plasma-assisted chemical vapor deposition process, each grown with a different [B]/[C] ratio (up to 20,000 ppm) in the gas phase. The developed boron-doped diamond (BDD) films are a promising semiconducting material for sensing and high-power electronic devices due to band gap engineering and thermal management feasibility. The increased boron concentration in the gas phase induces a decrease in the average grain size, consequently resulting in lower surface roughness. The BDD sheets grown with [B]/[C] of 20,000 ppm reveal the metallic conductivity while the lower doped samples show p-type semiconductor character. The charge transport at room temperature is dominated by the thermally activated nearest-neighbor hopping between boron acceptors through impurity band conduction. At low temperatures (<300 K), the Arrhenius plot shows a non-linear temperature dependence of the logarithmic conductance pointing towards a crossover towards variable range hopping. The activation energy at high temperatures obtained for lowly-doped sheets is smaller than for nanocrystalline diamond bonded to silicon, while for highly-doped material it is similar. Developed sheets were utilized to fabricate two types of diamond-on-graphene heterojunctions, where boron doping is the key factor for tuning the shape of the current-voltage characteristics. The graphene heterojunction with the low boron concentration diamond sheet resembles a Schottky junction behavior, while an almost Ohmic contact response is recorded with the highly doped BDD sheet of metallic conductivity. The free-standing diamond sheets allow for integration with temperature-sensitive interfaces (i.e. 2D materials or polymers) and pave the way towards flexible electronics devices.

Solid-State Synthesis and Thermoelectric Properties of Ge-Doped Tetrahedrites Cu12Sb4-yGeyS13

Ge-doped tetrahedrites Cu12Sb4-yGeyS13 (y = 0.1–0.4) were prepared using mechanical alloying and hot pressing. An X-ray diffraction analysis after mechanical alloying showed a single tetrahedrite phase without secondary phases. The tetrahedrite phase was stable after hot pressing at 723 K under 70 MPa. As the Ge content increased, the lattice constant decreased from 1.0343 to 1.0334 nm, which confirms that Ge was successfully substituted at the Sb sites. Ge-doped tetrahedrites exhibited p-type semiconductor characteristics. When Ge4+ was substituted for Sb3+, additional electrons were generated. Thus, the electrical conductivity decreased and the Seebeck coefficient increased due to the decrease in carrier (hole) concentration. For the Ge-doped specimen with y = 0.1, a maximum power factor of 0.87 mWm-1K-2 was obtained at 723 K. As the Ge content increased, the power factor decreased. However, as the Ge content increased, the electronic and lattice thermal conductivities decreased. Therefore, the substitutions of Ge at the Sb sites intensified both ionization impurity scattering and phonon scattering, resulting in very low thermal conductivities of 0.4–1.0 Wm-1K-1 at 323–723 K for y = 0.1–0.4. As a result, the highest dimensionless figure of merit ZT = 0.74 was obtained at 723 K for Cu12Sb3.8Ge0.2S13.

Evolution of Discharge Products on Carbon Nanotube Cathodes in Li–O2 Batteries Unraveled by Molecular Dynamics and Density Functional Theory

The performance of Li–O2 batteries (LOBs), such as capacity and overpotential, is closely related to the morphology of the discharge product. Here, the relationship between the growth behavior of Li2O2 on the surface of the carbon nanotube (CNT) cathodes and the cycle performance of LOBs was innovatively revealed based on molecular dynamics (MD) and density functional theory (DFT). Our results demonstrated that the growth of (Li2O2)n on the CNT surface mainly undergoes three stages: adhesion, branching, and connection. The stable gap between (Li2O2)n and the CNT surface was determined to be approximately 2.47 Å. Interestingly, the dense deposition thickness is positively correlated with the number of Li2O2 monomers. In addition, the formation of free Li2O2 directly induces the instability of (Li2O2)n and capacity loss. Moreover, armchair-type CNTs with larger diameters, especially single-walled CNTs and multi-walled CNTs with an odd number of tube walls were found to be more conducive to the stable growth of discharge products. Notably, (Li2O2)n is mainly composed of internal stable parts with low conductivity and amorphous components distributed on the surface with p-type semiconductor characteristics. Therefore, the regulation of the CNT structure and the preparation of catalysts to promote the conversion of Li2O2 from an ordered state to an amorphous structure play a vital role in breaking the technical bottleneck of LOBs. Our results identify the long-term controversial evolution mechanism of the product morphology, and the unique calculation ideas are also applicable to the intuitive exploration of the microscopic growth behavior of discharge products in other metal–air batteries.

Phase evolution, microstructure, microhardness and corrosion performance of CoCrFeNiNb x high entropy alloy coatings on 316 stainless steel fabricated by laser cladding

ABSTRACT FeNiCoCrNb x (x: molar ratio, x = 0, 0.1, 0.2, 0.3) high entropy alloy coatings (HEACs) were fabricated on 316 stainless steel (SS) by laser cladding (LC). Experimental results showed that the addition of Nb increased the lattice constant of FeNiCoCrNb high entropy alloy system. HEAC exhibited the transformation from columnar crystal at the interface to equiaxed crystal at the surface on the cross-sectional plane because of the change in the temperature gradient (G) and solidification rate (R). When x = 0.3, lamellar Laves phases appeared in ID. The microhardness of the four HEACs was 1.78, 2.19, 2.30 and 2.37 times that of 316 SS. The HEAC with x = 0.3 as well as 316 SS exhibited typical p-type semiconductor characteristics, which showed excellent corrosion resistance as indicated by the lowest of 2.46 × 10−9 A cm−2 and a larger passivation region with 2 times that of 316 SS.

Effects of pH and Cl− Content on Degradation Process of Pre-Passivated Stainless Steels in an Alkaline Solution

The degradation behavior of four prepassivated stainless steels (SSs) in the alkaline solutions with different Cl− concentrations and pH values were investigated by cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis and the X-ray photoelectron spectroscopy (XPS). The results indicated that the pH value and Cl− concentration, together with the phase ratio difference in the microstructure of SS, played a critical role in the degradation process of passive film. At low pH and high Cl− concentration, the passive film gradually enriched in Fe3+ and Cr3+ species and depleted in Fe2+ oxides and its self-regeneration process became more difficult. As the pH decreased, the passive film exhibited clear n-type and p-type semiconductor characteristics more clearly, and the decrease in dopant density well reflected the changes in Fe2+/Fe3+ ratio and electrochemical behavior. Based on the viewpoint of adsorption balance between OH− with inhibitory effect and Cl− with promotion effect on the degradation process, a mechanism for the degradation process of prepassivation film was proposed.