Dielectric properties of CaCu3Ti4O12 based multiphased ceramics

A “soft chemistry” method, the coprecipitation, has been used to synthesize the perovskite CaCu3Ti4O12 (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 + CaTiO3), and a three-phased (CCT + CaTiO3 + copper oxide (CuO or Cu2O)). 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

Hydrothermal synthesis of nanosized BaTiO3 powders and dielectric properties of corresponding ceramics

BaTiO3 fine powders were synthesized by hydrothermal method at 150 °C or 250 °C for 7 h, starting from a mixture of TiCl3 + BaCl2 or TiO2 + BaCl2. The size of the crystallites is close to 20 nm whatever the starting mixture and the reaction temperature. These powders are well crystallized and constituted of a mixture of the metastable cubic and stable tetragonal phases. The ceramics obtained after uniaxial pressing and sintering at 1250 °C for 10 h or 20 h present high densification (up to 99.8%). The Curie temperature (Tc) and the electrical permittivity ( r) of the ceramics strongly depend on the type of titanium source that has been used for preparing the powder and on the sintering dwell time. Particularly, Tc is shifted towards lower temperature when TiCl3 is used. The permittivity value at Tc of BaTiO3 sintered at 1250 °C for 10 h reaches 7000 and 11,000 with respectively TiCl3 and TiO2 used as titanium source

Thermal expansion, polarization and phase diagrams of Ba1−yBi2y/3Ti1−xZrxO3 and Ba1−yLayTi1−y/4O3 compounds

The thermal expansion properties of the ceramic compositions Ba1−yLayTi1−y/4O3 (y = 0.0, 0.026, 0.036, 0.054) and Ba1−yBi2y/3Ti1−xZrxO3 (y = 0.10; x = 0.0, 0.04, 0.05, 0.10, 0.15) were determined in the temperature range 120–700 K. We report the temperature-dependent measurements of the strain, thermal expansion coefficient and the magnitude of root mean square polarization. The results obtained are discussed together with the data on the structure and dielectric properties

Colossal and frequency stable permittivity of barium titanate nanoceramics derived from mechanical activation and SPS sintering

Highly dense barium titanate nanoceramics have been successfully prepared via a mechanical activation synthesis method and Spark Plasma sintering. Attractive electrical properties have been evidenced in these materials: a colossal permittivity, (3.5. 105) and low loss (0.07) at room temperature and 1 kHz, that are stable over a wide frequency range (from 40 Hz to 40 kHz). Surprisingly, the ferroelectric transition is still observed, for the first time to our knowledge, in these colossal permittivity materials

Elaboration and characterization of barium titanate powders obtained by the mechanical activation of barium nitrate and titanate oxide, and electrical properties of the ceramics sintered by SPS

The current work aims to reduce the energy required to obtain a high quality barium titanate nanocrystals via solid-state reaction. In order to achieve this challenge, Ba(NO3)2 and TiO2 were mechanically activated by high-energy ball milling, and then heat treated at moderate temperature (600 oC). When stoichiometric mixture was used, the formation of BT and minor BaCO3 and TiO2 impurities was observed. The use of Ba(NO3)2 excess leads to the formation of BT and a minor BaCO3 impurity. A simple acid wash treatment was used to remove the carbonate impurity and to provide a high purity BT. The powders were characterized by XRD, BET, Raman spectroscopy, and SEM-FEG. Spark Plasma Sintering (SPS) technique was used to get the dense nanoceramics. These materials show, at room temperature and at 1 kHz, colossal permittivity (ε = 105) associated with low dielectric loss (tg δ = 0.07)

Elaboration de poudres de titanates par chimie douce, caractérisation, mise en forme de céramiques et de couches, et propriétés électriques (application aux matériaux à très fortes valeurs de permitivité)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

From Synthesis to Applications: Copper Calcium Titanate (CCTO) and its Magnetic and Photocatalytic Properties

International audienceInvestigations focusing on electrical energy storage capacitors especially the dielectric ceramic capacitors for high energy storage density are attracting more and more attention in the recent years. Ceramic capacitors possess a faster charge-discharge rate and improved mechanical and thermal properties compared with other energy storage devices such as batteries. The challenge is to obtain ceramic capacitors with outstanding mechanical, thermal and storage properties over large temperature and frequencies ranges. ABO(3) as a type of perovskites showed a strong piezoelectric, dielectric, pyroelectric, and electro-optic properties useful as energy storage and environmental devices. CaCu3Ti4O12 (CCTO) perovskite with cubic lattice (Im3 symmetry) was discovered to have a colossal dielectric constant (10(4)) that is stable over a wide range of frequencies (10 Hz-1 MHz) and temperature independence (100-300 K). The origin of this high dielectric constant is not fully established, specially because it is the same for single crystal and thin films. In this review, the history of CCTO will be introduced. The synthesis and the sintering approaches, the dopant elements used as well as the applications of CCTO will be reported. In addition to dielectrical properties useful to energy storage devices; CCTO could serve as photocatalytic materials with a very good performance in visible light

Hydrothermal synthesis of nanosized BaTiO3 powders and dielectric properties of corresponding ceramics

International audienceBaTiO3 fine powders were synthesized by hydrothermal method at 150 °C or 250 °C for 7 h, starting from a mixture of TiCl3 + BaCl2 or TiO2 + BaCl2. The size of the crystallites is close to 20 nm whatever the starting mixture and the reaction temperature. These powders are well crystallized and constituted of a mixture of the metastable cubic and stable tetragonal phases. The ceramics obtained after uniaxial pressing and sintering at 1250 °C for 10 h or 20 h present high densification (up to 99.8%). The Curie temperature (Tc) and the electrical permittivity ( r) of the ceramics strongly depend on the type of titanium source that has been used for preparing the powder and on the sintering dwell time. Particularly, Tc is shifted towards lower temperature when TiCl3 is used. The permittivity value at Tc of BaTiO3 sintered at 1250 °C for 10 h reaches 7000 and 11,000 with respectively TiCl3 and TiO2 used as titanium source

Caractérisation de céramiques massives et de couches épaisses préparées à partir des nanopoudres de BaTiO3.

Des poudres fines de BaTiO3 (BT) sont synthétisées par la méthode hydrothermale ? 250 ?C pendant 7 heures. Deux mélanges précurseurs différents sont utilisés : TiCl3 + BaCl2 et TiO2 + BaCl2. La taille des cristallites résultante est voisine de 20 nm indépendamment du mélange initial. Ces poudres sont alors employées pour préparer des céramiques massives (pastilles) et des couches épaisses déposées sur substrat plan. L'influence des précurseurs et du type de mise en oeuvre est mise en évidence en étudiant la permittivité tant dans le domaine des températures que des fréquences

Colossal and frequency stable permittivity of barium titanate nanoceramics derived from mechanical activation and SPS sintering

International audienceHighly dense barium titanate nanoceramics have been successfully prepared via a mechanical activation synthesis method and Spark Plasma sintering. Attractive electrical properties have been evidenced in these materials: a colossal permittivity, (3.5. 105) and low loss (0.07) at room temperature and 1 kHz, that are stable over a wide frequency range (from 40 Hz to 40 kHz). Surprisingly, the ferroelectric transition is still observed, for the first time to our knowledge, in these colossal permittivity materials