In cation–anion co-doping, rare earth elements excel at regulating the electronic structure of perovskites, leading to their improved photocatalytic performance. In this regard, the impact of co-doping rare earth elements at the Ba and Ti sites in BaTiO₃ on its electronic and photocatalytic properties was thoroughly investigated based on 2 × 2 × 2 supercell structures of BaTiO₃ with different La concentrations of 12.5% and 25% using DFT calculations. The band structure, density of states, charge density difference, optical properties, and the redox band edge of the co-doped models mentioned above were analyzed. The results indicated that the BaTiO₃ structure co-doped with 25% La at the Ti site exhibited higher absorption in the visible range and displayed a remarkable photocatalytic water-splitting performance. The introduced La dopant at the Ti site effectively reduced the energy required for electronic transitions by introducing intermediate energy levels within the bandgap. Our calculations and findings of this study provide theoretical support and reliable predictions for the exploration of BaTiO₃ perovskites with superior photocatalytic performances.

The ionic transport process is an important counterpart to charge transport in oil‐paper insulation, and it significantly impacts oil flow electrification at the oil‐paper interface. Despite this, the dynamics of this phenomenon and the underlying mechanisms remain unclear, particularly at the molecular level. To understand this fundamental aspect, we conduct Molecular Dynamics study on the transport behaviour of an impurity ion in different oil‐paper insulation models under various external electric fields. Different influence factors, such as external electric fields, temperatures, and local structural characteristics, are investigated in relation to the corresponding ionic mobility in different polymer models. According to the simulations, ionic mobility and its response to electric fields are higher in weaker electrostatic models. As a result, mineral oil exhibits the highest ionic mobility and the most substantial enhancement of ionic mobility by external electric fields, followed by vegetable oil, oil‐paper blends, and insulating paper. This significant deviation in ionic mobility between oil and paper leads to the formation of an electric double layer near the oil‐paper interface. The underlying physical mechanisms of different ionic mobility and its response to the electric field in different polymer models could be explained by the different polymer structural influences in terms of interaction energy and coordination numbers in a static manner, as well as by the interactions between the impurity ion and its surrounding atoms in terms of lifetime correlation functions and velocity autocorrelation functions in a dynamic manner. In addition, the influence of temperature on ionic mobility in mineral and vegetable oil is examined, and their activation energies are calculated. Advancing in the fundamental understanding of the dynamics of the ion transport process in oil‐paper insulation is vital to improving their insulating properties for oil‐impregnated power transformers.

As one of the weakest points in high-voltage direct current cables and accessories, the accumulation of space charges at the crosslinked polyethylene (XLPE)/ethylene propylene diene monomer (EPDM) interface coated with silicone oil is crucial to insulating properties. The physical mechanisms underlying this charge accumulation and dissipation phenomenon remain unclear, particularly at the molecular level. Thus, the interfacial space charge accumulation and dissipation behavior at EPDM/XLPE, EPDM/non-polar dimethyl silicone oil (PDMS)/XLPE, and EPDM/polar fluorinated silicone oil (PMTFS)/XLPE interfaces was measured using pulsed electroacoustic (PEA) method, and molecular simulation techniques were employed to calculate the electronic properties across those interfaces. It was found that the transformation law of the interfacial charge polarity does not completely align with the Maxwell–Wagner (MW) model, which is related to the contact type of the interface (with or without silicone oil and the type of silicone oil) and the voltage polarity. The presence of a high interfacial potential barrier is an important factor behind the fact that the transformation law of the interfacial charge polarity does not align with the MW model. The high hole potential barrier (greater than 1 eV) of EPDM/XLPE and EPDM/PMTFS is the reason why the interfacial charges of EPDM/XLPE and EPDM/PMTFS/XLPE remain always positive as the applied negative voltage and temperature increases. Due to the low potential barrier of the EPDM/PDMS/XLPE interface, the polarity of the interfacial charge is always consistent with the polarity of the voltage applied to the medium with a greater conductivity. At 40 °C and 60 °C, EPDM/XLPE and EPDM/PMTFS/XLPE positive interface charge accumulation is significantly reduced compared to that observed at room temperature under a negative voltage, which is attributed to the enhanced charge injection and migration of XLPE with rising temperature. This study provides theoretical insights for finding an effective coating material to reduce charge accumulation at the cable accessory interface.

Despite the fact that doping nanoparticles into insulating transformer oil has proven to be an effective method of enhancing its dielectric and electrical properties, it remains unclear how different types and surface conditions of nanoparticles may affect their dielectric and electrical properties. Therefore, the effect of doping various types of BN nanoparticles (nanosphere, nanotube, and nanosheet) in insulating mineral oil (MO) on the diffusion properties of water molecules and electrical properties across the BN/MO interface was investigated using molecular dynamics (MD) and Density Functional Theory (DFT) simulations. Our results show that different surface morphology and grafted functional groups in different types of BN nanoparticles have a significant impact both on the water diffusion behavior and the interfacial potential barrier across the interface between BN and MO. In the MO system directly doped by BN nanospheres, water diffusion behavior is not significantly restricted. However, grafting -NH₂ polar groups onto the BN nanoparticle surface may significantly limit the diffusion behavior of water due to the strong attraction between the -NH₂ polar groups and water molecules; the most significant effect is with nanospheres, followed by nanotubes and nanosheets. In terms of electrical properties across the interface between BN and MO, the h-BN surface (derived from BN nanosheets and nanotubes) acts as a trap for electrons in MO (−0.59 eV), while the c-BN surface (derived from BN nanospheres) acts as a potential barrier for electrons in MO (1.45 eV), and it is noteworthy that the presence of water molecules near the interface between BN and MO has little impact on the potential barriers. Advancing a fundamental understanding of the electrical and water diffusion properties of MO in correlation with the surface morphology of different types of nanoparticles is key to improving the insulation properties of oil-impregnated power transformers.

The energy band structure is crucial for solid insulation research. The traditional thermally stimulated current is used mostly for direct trap estimation but has some limitations, which can be overcome by the space charge decay method. With the help of a modified pulsed-electro acoustic system, we perform the test under different low temperatures and obtain a more comprehensive band spectrum including shallow traps and different polarities. This study chooses isotactic polypropylene (PP) to investigate in a temperature range of −120 to 20 °C. Signal processing and recovery are considered. Two basic trap estimation methods are compared and the one based on the modified isothermal relaxation current theory is used here. The electron and hole trap densities near different electrode interfaces are considered in the experiment. In the preliminary results, it is found that the traps tend to move toward a shallow direction with a decrease in temperature. A model of the retrapping process caused by phonon scattering is put forward to explain the results. The retrapping possibility is, therefore, assumed to follow a power relation with temperature. An attempt to rectify the trap depth is performed on such a model by numerical approximation and reaches the result that the retrapping possibility may be dependent upon the second power of temperature. Finally, the broadband energy spectrum is calculated after correction. In the normalized coordinate system, the traps in PP are mainly distributed in a deep range; few shallow traps are found maybe because the space charge density is low.