The effect of silver doping on the DC‐voltage resistance failure of lead‐based relaxor ferroelectrics was investigated via temperature‐humidity‐bias (THB) testing, scanning electron microscopy, X‐ray diffraction spectroscopy, and electrical measurements. The failure rate of silver‐doped specimens was found to increase significantly with the doping level during the THB test. However, some degraded specimens can partially recover their electrical properties after a few days of storing in natural conditions. X‐ray diffraction analysis showed that silver could be incorporated into the perovskite lattice in the range of silver contents studied. The presence of an inner‐bias field in the degraded ceramics was first demonstrated through hysteresis property measurement. Based on these results, it was inferred that the accumulation of oxygen vacancies under DC‐voltage should be responsible for the inner‐bias field, which consequently resulted in the increase of electronic defects in the ceramics.
Resistance measurement, P-E hysteresis measurement, and transmission electron microscope and energy dispersive analysis of x-rays (TEM-EDAX) analysis were used to study the resistance failure of lead magnesium niobate-based multilayer ceramic capacitors (MLCC) under dc voltage. It was found that the failure rate of MLCC with 1/9 Pd/Ag internal electrodes was 10 times that of MLCC with 3/7 Pd/Ag electrodes after the temperature-humidity-bias test (THB). Voltage shifts of hysteresis loops showed that an internal bias field between electrodes of MLCC was formed after THB test. Ag diffusion from electrodes into the ceramics during cofiring was examined through TEM-EDAX analysis. It was also found that the degraded specimens could be partially restored after storing under natural condition. On the basis of these results, the failure mechanism was established that oxygen vacancies induced by Ag diffusion accumulated under the external bias field, which increased the concentration of electronic defects, thereby resulting in the resistance failure of MLCC.
An advanced microencapsulation for n-octadecane has been successfully developed via UV photoinduced polymerization in this study, which was characterized by some superior qualities (e.g. rapid microencapsulation, energy-saving and environment-friendly) compared to conventional microencapsulation process. The morphology, microstructure and properties of the microencapsulated n-octadecane with poly (aliphatic polyurethane acrylate) and poly (allyl methacrylate) as shell were respectively investigated by FE-SEM, TEM and DSC. The effects of UV irradiation time, shell material types and feed ration of shell-forming monomer to n-octadecane on the morphology and structure were investigated in detail. Furthermore, the photoinduced microencapsulation mechanism was interpreted clearly as well. Besides, the phase change properties were studied as well.
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