[en] Enhanced corrosion-resistant Ni-Cu-P amorphous coatings were applied to AZ91D magnesium alloy substrates using an integrated approach that included direct-current (DC) copper pre-plating and electroless Ni-Cu-P plating at varying CuSO₄ concentrations. The effects of CuSO₄ concentration on the microstructure, electrochemistry behavior and corrosion rate of Ni-Cu-P coatings and the adhesion between the Ni-Cu-P coating and the magnesium alloys substrate were investigated. The results indicated that the surface of the Ni-Cu-P ternary coating which integrated well with the magnesium alloys substrate exhibited heterogeneous cell structure with relatively flat and dense structure. When the CuSO₄ concentration was 0.8 g/L, the mass fraction of P in the coating was 9.06 wt% meaning amorphous Ni-Cu-P coating. The results of the Nyquist and Bode graph, corrosion rate, corrosion morphologies and of the Ni-Cu-P coatings with different CuSO₄ addition indicated that the corrosion resistance reached optimization with corrosion potential of -0.31 V, the corrosion current density of 0.0039 A/cm² when the CuSO₄ concentration is 0.8 g/L. Furthermore, the adhesion test confirmed that the adhesion of Ni-Cu-P coatings improved gradually as the CuSO₄ concentration increased and exhibited optimum when added 1.0 g/L CuSO₄ . The obtained Ni-Cu-P coating with amorphous structure prevented effectively magnesium alloy from corrosion. (author)

[en] Double-layer Ni-P coatings with low phosphorus content in the inner layer and high phosphorus content in the outer layer and Ni-Mo-P composite coatings are successfully prepared on the surface of AZ91D magnesium alloy by chemical plating process. The microstructures, friction and corrosion resistance of double-layer Ni-P and Ni-Mo-P coatings are studied in comparison. Meanwhile, the deposition and corrosion resistance mechanism for the coatings are investigated. Results convey that both Ni-P and Ni-Mo-P coatings showcase an amorphous structure. The coating possesses denser and more homogeneous structure with the co-doping of Mo. The micro-indentation hardness (859.7 HV) and friction coefficient (0.58) of Ni-Mo-P coatings show that the ternary alloy coating is firmly bonded to the magnesium alloy substrate. Besides, the Ni-Mo-P coatings demonstrate exceptional wear resistance attributed to Mo co-deposition, fostering grain refinement and facilitating the growth of passivation films. (author)

[en] Extruded polycrystalline pure magnesium (Mg) with fine grain size (~1.2 µm) exhibits ductility of over 100% at room temperature, in spite of the presence of a strong basal texture. In this study, a set of complementary in-situ characterisation techniques over multiple-length scales were utilised to reveal the deformation modes enabling such ductility. Synchrotron X-ray diffraction results show that the elastic lattice strain of fine-grained sample for tensile elongation up to ~55% is 3–10 times lower than that in the coarse-grained sample, indicating the absence of significant strain accumulation inside fine grains and potential inter-granular deformation in bulk. In-situ scanning electron microscopy validates the predominant operation of the inter-granular deformation, and it further reveals that the inter-granular deformation occurs by the relative sliding between groups of grains having similar orientations. The deformation resulting from such sliding is substantial, and it is accommodated by the rotation of grains located between slid grouped grains, from hard to softer orientations to allowing dislocation slip to readily occur. The accommodating mode of dislocation slip is further supported by in-situ transmission electron microscopy observations. Dislocations glide readily to, and annihilate at, grain boundaries. The observations and direct evidences presented herein suggest that the major deformation mode is sliding between grouped grains that is accommodated by grain rotation and dislocation slip, in contrast to dislocation slip in coarse-grained Mg. The coordinated deformation processes postpone the occurrence of localised stress concentration and greatly increases the ductility of pure Mg at room temperature.

[en] By first-principles, we study the magnetic properties of (Mn, N)-codoped ZnO, with various interstitial structures of H. Besides, hydrogen motion in ZnMnON has been investigated too. Results show that a mobile H in (Mn, N)-codoped ZnO may be favorably formed a stable –Mn–H–N– complex, and that the ferromagnetism strongly depends on the geometrical configurations of these impurities. The strong hybridization between H-impurity band and the Mn 3d minority spin states at the Fermi level results in the FM coupling between the spins of Mn and N, which is similar with the spin–split donor impurity band model

[en] The influences of Mn doping on the structural quality of the Zn_xMn_1−xO:N alloy films have been investigated by XRD. Chemical compositions of the samples (Zn and Mn content) and their valence states were determined by X-ray photoelectron spectrometry (XPS). Hall effect measurements versus temperature for Zn_xMn_1−xO:N samples have been designed and studied in detail. The ferromagnetic transitions happened at different T_C should explain that the magnetic transition in field-cooled magnetization of Zn_1−xMn_xO:N films at low temperature is caused by the strong p–d exchange interactions besides magnetic transition at 46 K resulting from Mn oxide, and that the room temperature ferromagnetic signatures are attributed to the uncompensated spins at the surface of anti-ferromagnetic nano-crystal of Mn-related Zn(Mn)O. - Highlights: ► The influences of Mn doping on the fine structure of the Zn_xMn_1−xO:N alloy films have been investigated. ► The physical mechanisms of the magnetic transition in field-cooled magnetization of Zn_1−xMn_xO:N films have been discussed. ► The electron transport properties of Zn_xMn_1−xO:N alloy films have been discussed.

[en] Mn doped Zinc oxide (ZnO) thin films were prepared by metal organic chemical vapor deposition (MOCVD) technique. Structural characterizations by X-ray diffraction technique (XRD) and photoluminescence (PL) indicate the crystal quality of ZnO films. PL and Raman show a large fraction of oxygen vacancies (V_O²⁺) are generated by vacuum annealed the film. The enhancement of ferromagnetism in post-annealed (Mn, In) codoped ZnO could result from V_O²⁺ incorporation. The effect of V_O²⁺ on the magnetic properties of (Mn, In) codoped ZnO has been studied by first-principles calculations. It is found that only In donor cannot induce ferromagnetism (FM) in Mn-doped ZnO. Besides, the presence of V_O²⁺ makes the Mn empty 3d-t_2g minority state broadened, and a t_2g-V_O²⁺ hybrid level at the conduction band minimum forms. The presence of V_O²⁺ can lead to strong ferromagnetic coupling with the nearest neighboring Mn cation by BMP model based on defects reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Mn 3d electrons trapped in oxygen vacancies.

[en] ZnO:Mn films doped with indium (In) and nitrogen (N) have been grown on sapphire and ZnO template substrates, respectively by the metal-organic chemical vapor deposition method. All these samples show clear hysteresis loops and saturation magnetizations (M_S) at room temperature characterized by a vibrating sample magnetometer in a Quantum Design Physical Property Measurement System. For the n-type ZnO:(Mn, In) and ZnO:Mn samples, the mechanism of the room-temperature ferromagnetism (RTFM) has been ascribed to the interactions between BMPs, which are formed by the magnetic coupling between Mn ions and the oxygen vacancies (V_O) defects. However, for the p-type ZnO:(Mn, N) samples, a single mechanism is not fully responsible for the measured RTFM. In contrast with the role of V_O in ZnO:(Mn, In) and ZnO:Mn system, the incorporation of V_O in ZnO:(Mn, N) would weaken the FM. For the ZnO:(Mn,N), the observed highest M_S is mainly ascribed to the RKKY interactions from the N 2p and Mn 3d ferromagnetic exchange coupling. Besides, a density functional theory simulation also indicates that ferromagnetic coupling may be enhanced by V_O in n-type ZnO:(Mn, In) and ZnO:Mn films, while the V_O defects in p-type ZnO:(Mn:N) films act oppositely, that may weaken the ferromagnetic coupling. - Highlights: • ZnO:Mn films doped with indium and nitrogen have been grown on sapphire and ZnO template substrates. • Room-temperature ferromagnetism has been observed in ZnO:Mn films doped with indium and nitrogen films. • Oxygen vacancies (V_O) in n-type Mn doped and (Mn, In) codoped ZnO would enhance the room-temperature ferromagnetism. • The V_O in p-type (Mn, N) codoped ZnO films would weaken the ferromagnetic coupling