Development of microelectronic devices is driven by a large demand for faster and smaller systems. In the near future, colossal permittivity in nanomaterials will play a key role in the advances of electronic devices. We report on "colossal" permittivity values achieved in dense ceramics displaying ultrafine grain size ranging from 70 nm to 300 nm. Relative permittivity values of ∼ 10 6 at 1 kHz (0.1 < tand < 0.7) were obtained for Ba 0.95 La 0.05 TiO 3-x ceramics. The colossal effective permittivity is related to an interfacial polarization and is achieved in nanomaterials by the activation of a high number of carriers and their trapping at the interfaces. Polarization carriers involving Ti 3+ polaron is proposed to be at the origin of the observed colossal permittivity. These results may have an important technological impact since these ceramics display ultrafine grain size opening a new route to the fabrication of very thin dielectric films.High permittivity values such as e r ∼ 10 000 were reported in polycrystalline BaTiO 3 , a well known ferroelectric material.[1] Decreasing the grain size below 0.7 lm of the BaTiO 3 ferroelectric ceramic was shown to yield unrelieved stresses resulting in smaller permittivity values.[2] Indeed, colossal permittivity values up to 200000 at room temperature were achieved in BaTiO 3 micronic grain size materials in which preparation included incorporation of metallic layers in a complex multi step process. [3,4] The achievement of high permittivity values in this material was ascribed to interfacial polarization phenomena. Recently, giant permittivity values were reported in hexagonal barium titanate (h-BaTiO 3 ) single crystals. [5,6] High permittivity values around 10 5 measured on the oxygen deficient materials were explained by a MaxwellWagner interfacial polarization effect due to the presence of interfacial boundaries consisting of crystal defects such as screw dislocations. Nevertheless, the internal interfaces as well as the nature of the polarization carriers in the h-BaTiO 3 single crystals were not fully identified. Within the last few years, a large class of dielectric materials displaying colossal permittivity was proposed [7][8][9] with colossal dielectric con- [10] The large permittivity values of this material being attributed to the well established IBLC effect.[11] According to the brick layer model, the effective permittivity e eff of the microstructure can be expressed as e eff = e gb t g /t gb where e gb is the grain boundary permittivity and t g and t gb are the thickness of the grain and grain boundary, respectively.[12]Thus the IBLC mechanism is usually associated with enhanced grain size. In this context, a decrease of the average grain size should not favor the IBLC effect and colossal permittivity in ultrafine ceramics, to our knowledge, has not been reported. In this communication, we discuss the "colossal" permittivity values achieved in BaTiO 3-x and Ba 0.95 La 0.05 TiO 3-x materials exhibiting very small grain size (< 300 nm). Dense dielectrics...

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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 10 6 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.

A "soft chemistry" method, the coprecipitation, has been used to synthesize the perovskite CaCu 3 Ti 4 O 12 (CCT). Three main types of materials were obtained for both powders and sintered ceramics: a monophased consisting of the pure CCT phase, a biphased (CCT + CaTiO 3 ), and a three-phased (CCT + CaTiO 3 + copper oxide (CuO or Cu 2 O)). These ceramics, sintered at low temperature, 1050 • C, present original dielectric properties. The relative permittivity determined in the temperature range (−150 < T < 250 • C) is significantly higher than the one reported in the literature. Internal barrier layer capacitor is the probable mechanism to explain the particular behaviour. Moreover, the presence of a copper oxide phase beside the perovksite CCT plays an important role for enhancing the dielectric properties.

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International audienceDielectric properties of CaCu3Ti4O12 (CCTO)-based ceramics and thick films (e ∼50m) prepared from powders synthesized by a soft chemistry method (co-precipitation) are presented and discussed. The characteristics of pellets and thick films are compared. The pellets exhibit high values of the dielectric permittivity (εr ∼1.4×105) and relatively small dielectric losses (tan δ ∼0.16) at 1 kHz and room temperature. These properties are independent of the nature of the metallization of the electrodes. In addition, the dielectric permittivity decreases when the diameter of the electrodes of the pellets increases, while the losses remain constant. This result, which is strongly related to the nature of the dielectric material in between the electrodes, constitutes a strong indication that the high dielectric permittivity values observed in this material are not related to an interfacial (electrode material) related mechanism but is an internal barrier layer capacitor (IBLC) type. Very high values of the dielectric permittivity of CCTO thick films are measured (εr ∼5×104). The differences in dielectric permittivity between thick films and dense pellets may be attributed to the difference in grain size due to different CuO contents, and to the different reactivity of the materials

We report a dielectric constant of up to 5.4 × 105 at room temperature and 1 kHz for CaCu3Ti4O12 (CCTO) ceramics, derived from multiphase powders (coprecipitation products), made by a “chimie douce” (coprecipitation) method, and then sintered in air. The sintered products are pure‐phase CCTO ceramics. The high dielectric constant is achieved by tuning the size of grains and the thickness of grain boundaries. The grain growth is controlled by varying the concentration of excess CuO in the initial powder (calcined coprecipitation products) between 1 and 3.1 wt%. The dielectric constant of pure CCTO ceramics increases with the initial CuO concentration, reaching its maximum at 2.4 wt% of CuO. A further increase of excess CuO in powders results in a permittivity decrease, accompanied by the formation of CuO as a separate phase in the sintered products. The unusual grain growth behavior is attributed to a eutectic reaction between CuO and TiO2 present in the initial powder.