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Ferroelectric tunnel junctions (FTJs) with multi-quantum well structures are proposed and the tunneling electroresistance (TER) effect is investigated theoretically. Compared with conventional FTJs with monolayer ferroelectric barriers, FTJs with single-well structures provide TER ratio improvements of one order of magnitude, while FTJs with optimized multi-well structures can enhance this improvement by another order of magnitude. It is believed that the increased resonant tunneling strength combined with appropriate asymmetry in these FTJs contributes to the improvement. These studies may help to fabricate FTJs with large TER ratio experimentally and put them into practice.

Tunneling electroresistance (TER) effect was investigated in Pt/MgO/Pt/PbTiO3/Pt ferroelectric tunnel junctions (FTJs) theoretically. Compared to Pt/MgO/PbTiO3/Pt FTJs with the same composite barrier thickness (unit cells), FTJs with a thicker Pt interlayer (2 ∼ 3 unit cells) could provide 1 ∼ 6 orders of magnitude improvement in the TER ratio in a wide range of polarization. Resonant tunneling effect and/or enhanced asymmetry of the potential energy profile induced by the resonant-tunneling structure of MgO/Pt/PbTiO3 in Pt/MgO/Pt/PbTiO3/Pt FTJs is responsible for the TER improvement.

Three-component high-elasticity nanocomposites consisting of methyl vinyl silicone rubber (VMQ) and nanosized barium titanate (BT) and carbon black (CB) were fabricated. Studies on dielectric property and elastic modulus of the CB-BT/VMQ nanocomposites showed that the composites had a low percolation threshold (fc=0.0355) due to the use of nanosized CB, and the maximum of dielectric permittivity was 960 at 103 Hz with a low dielectric loss (0.04). When the concentration of CB was close to fc, the dielectric permittivity was sensitive to the change in temperature. The present dielectric properties and excellent elasticity would satisfy the need in practical applications, especially in some fields of cable accessories and heat sensitive sensors.

Silver/polyimide composite films were prepared through simple ultrasonic dispersion and subsequent in situ polymerization process. Dependence of dielectric properties of the films on volume fraction of Ag particles, frequency, and temperature was investigated. The percolation threshold of the films was only 0.122, which was lower than the theoretical value (0.16). The effective dielectric permittivity of the film with 12.5vol% of Ag fillers achieved 400 at 103Hz. The relative tolerance of dielectric permittivity of the film with 12.0vol% of Ag fillers in wide temperature range was less than 4.0%, which would satisfy the need in practical applications.

To explore the effect of aspect ratio (AR) of nanotubes on conductivity and resistance-pressure sensitivity, four kinds of multiwall carbon nanotubes (MWNT) with different aspect ratios (AR=50, 75, 333, and 500) were dispersed into methylvinyl silicone rubber (VMQ) to fabricate the MWNT/VMQ nanocomposites. Results show that the composites with low concentration nanotubes at low AR value show great resistance-pressure sensitivity. High AR is not beneficial for the improvement of conductivity, and at the same concentration of MWNT, the composites with high AR tubes display large resistance-pressure sensitivity. The sensitivity is dependent on the quantity of conductive channels formed in the composites.

Nanocomposites consisting of methylvinyl silicone rubber (VMQ) with excellent elasticity as polymer matrix and multiwall carbon nanotube (MWNT) with large slenderness ratio and high conductivity as filler were fabricated by a solution method and subsequently hot pressing technology. Studies on dielectric property and resistance-pressure sensitivity of the MWNT/VMQ composites showed that there was a giant dielectric constant and significant resistance-pressure sensitivity as the concentration of MWNT was near a low percolation threshold, fc≈0.012. After the composite applied an enough pressure for long time, the resistance-pressure sensitivity still shows an excellent reproducibility due to the good dispersion and low loading of MWNT.

The effects of γ-aminopropyltriethoxy silane coupling agent on electrical properties in multiwall carbon nanotube/methylvinyl silicone rubber nanocomposites were studied. The results showed that the modified nanotubes could be dispersed homogeneously and that they had a tight bonding with the rubber matrix. The concentration of coupling agent played a crucial role in deciding the conductivity and the electrical properties of the nanocomposites exhibited strong dependences on temperature and pressure. Dependences of electrical properties on temperature and pressure were also improved by increasing the content of coupling agent.