Colossal dielectric permittivity of BaTiO3-based nanocrystalline ceramics sintered by spark plasma sintering

In pursuit of high permittivity materials for electronic application, there has been a considerable interest recently in the dielectric properties of various perovskite oxides like calcium copper titanate or lanthanum doped barium titanate. When processed in a particular way, this later material present at ambient temperature and at f=1 kHz unusual interesting dielectric properties, a so called “colossal” permittivity value up to several 106 with relatively low dielectric losses. Moreover and contrary to what is classically expected and evidenced for this type of materials, no temperature dependence is observed. This behavior is observed in nanopowders based ceramics. An assumption to explain the observed properties is proposed. These results have important technological applications, since these nanoceramics open a new route to the fabrication of very thin dielectric films

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Broadband dielectric spectroscopy of multilayer graphene/epoxy nanocomposites

International audienceGraphene is a carbon-based allotrope material which, since very few years, appears as very exciting due to incredible physical properties such as a high electron mobility (250,000 cm 2 /Vs), a high thermal conductivity (5,000 W/mK) and a high Young's modulus (1 TPa). Obtained from the exfoliation of graphite pristine in the form of multilayer graphene (MLG) nanoplatelets, it focuses an increasing attention when mixed to a polymer matrix to produce MLG/polymer nanocomposites. Up to now, few studies have mainly reported on the effects on the thermal conductivity of various MLG/polymer nanocomposites. However, no study has been led on their dielectric properties. In this paper, we propose to study the impact of MLG on the dielectric permittivity and losses of an epoxy nanocomposite with different low nanoflakes filler contents from 0.005 to 0.5 wt.%, chosen below the electrical percolation threshold. The study will be performed both in wide temperature and frequency ranges in order to highlight the influence of the MLG nanoplatelets on the epoxy relaxation dynamics using a broadband dielectric spectrometer from Novocontrol. The MLG loading causes an increase of the polarizability of the composite material and thus the dielectric losses. At high temperature, at small MLG additions, the graphene particles interfere with the cooperative movements associated with the vitreous transition temperature, increasing the permittivity and decreasing the losses

Low frequency dielectric response of multilayer graphene/epoxy nanocomposites

International audienc

Novel electrical conduction properties obtained in few-layer graphene/epoxy nanocomposites

In this paper, we propose to study the impact of very low filler content (0.005 wt.%) of graphite nanoflakes (80 nm), multi-layer (5-20 nm) and few-layer (1-2 nm) graphene on the electrical conductivity of an epoxy nanocomposite. The results highlight that an improvement of the quality of the exfoliation process of graphene, particularly in few-layer graphene/epoxy, allows decreasing the DC electrical conductivity (by a factor 100 compared to neat epoxy) in a large range of electric field from 1 to 10 kV/mm. This novel property could allow decreasing space charge trapping within the insulator bulk at the origin of long-term electrical ageing