[en] Atomic force microscopy (AFM), a powerful, high-resolution imaging technique for determining the structure of surface, was used to examine the growth of the oxide film formed on 304 stainless steel in dilute sulfuric acid solution by using alternating voltage (AV) passivation. Transmission electron microscopy (TEM) was also used to investigate the growth of the film. It was pointed out that there were pores in the film during AV passivation, causing the oxide to grow rapidly. The site of pores changes continuously with the change of the morphology of the substrate caused by active dissolution under lower potential part of square wave electric field (E_L), this make the substrate dissolved to a polishing interface during AV passivation

[en] Highlights: • ZnO linear resistors have been studied comprehensively with different contents of La₂O₃. Structural and morphological characteristics of the samples were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. The property of resistivity-frequency reveals that the samples could be applied in high-frequency electric field. The dielectric property indicates Maxwell-Wagner interfacial polarization exists in the matrixes. • La³⁺ can be used as donor doping, to reduce the height of barrier at the grain boundary, further improving linear properties. When the doping amount of La₂O₃ is 1 wt%, The resistance temperature coefficient is -6.63×10^-3/°C, the minimum values of the barrier height and the nonlinear coefficient are 0.0787 eV and 1.09, respectively. -- Abstract: ZnO linear resistors have anticipated application prospect in electrical and electronic industry, but the study of La₂O₃ doping is still poor. In this paper, the ZnO linear resistors doped with Al₂O₃, MgO, SiO₂ and La₂O₃ were prepared by the conventional solid-state sintering method, and the effects of La₂O₃ doping on the microstructure and comprehensive electrical properties were studied. Structural and morphological characteristics of the samples were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. The property of resistivity-frequency reveals that the samples could be applied in high-frequency electric field. The dielectric property indicates Maxwell-Wagner interfacial polarization exists in the matrixes. With La₂O₃ content of 1 wt%, ZnO linear resistors have the best linear performance: the grain size is relatively uniform, the resistance temperature coefficient α_T is − 6.63 × 10⁻³/°C, and the nonlinear coefficient α is 1.09. The comprehensive analysis of the influence of La₂O₃ doping on the electrical properties is of important significance for preparing ZnO linear resistors with excellent electrical properties.