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Ca Cu 3 Ti 4 O 12 ceramics has been prepared by the conventional solid-state reaction method under different sintering conditions. Dielectric properties have been investigated in the temperature range of 25–350°C within the frequency range of 40Hz–10MHz. It has been found that both the dielectric constants and the grain sizes increase with the sintering time. A relaxation has been observed in the frequency range of 100Hz–100kHz, apart from the one already known in the frequency range higher than 100kHz. High-temperature dielectric dispersion shows one large low-frequency response and two Debye-type relaxations. Activation energy values of these two relaxations are 0.084 and 0.678eV, respectively. An equivalent circuit model is suggested, which well explains the dielectric dispersion.

Mn doping-induced structural and magnetic transformations in the antiferroelectric phase of the Bi1−xNdxFeO3 perovskites J. Appl. Phys. 112, 064105 (2012) Neutron diffraction study of stability and phase transitions in Cu-Sn-In alloys as alternative Pb-free solders J. Appl. Phys. 112, 053520 (2012) Communication: From graphite to diamond: Reaction pathways of the phase transition J. Chem. Phys. 137, 101101 (2012) Structural study in highly compressed BiFeO3 epitaxial thin films on YAlO3 A lead-free ceramic with the composition ͑K 0.55 Na 0.45 ͒ 0.965 Li 0.035 Nb 0.80 Ta 0.20 O 3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d 33 a͒ Electronic mail: zhangjialiang@sdu.edu.cn. APPLIED PHYSICS LETTERS 95, 022909 ͑2009͒

BaTiO3 ceramics with a high piezoelectric coefficient have been successfully obtained through the conventional solid-state reaction route starting from ordinary BaCO3 and TiO2 powders. The ceramics sintered at 1210 °C exhibit excellent piezoelectric properties of d33 = 419 pC N−1 and kp = 0.453 with tan δ = 1.36% at room temperature. The crystallographic structure, the microstructure and the domain pattern were investigated. It has been revealed that d33 increases and the average domain width in the poled BaTiO3 ceramics remains approximately constant at around 240 nm with the decrease in the average grain size from 9.5 to 2.0 µm. From the analysis, we suggest that the largeness of the domain wall is an important factor, which significantly influences the piezoelectric properties.

Ca Cu 3 Ti 4 O 12 (CCTO) ceramics are prepared by the conventional solid-state reaction method under various sintering temperatures from 1000to1120°C at an interval of 10°C. Microstructures and crystalline structures are examined by scanning electronic microscopy and x-ray diffraction, respectively. Dielectric properties and complex impedances are investigated within the frequency range of 40Hz–110MHz over the temperature region from room temperature to 350°C. It has been disclosed that the microstructures can be categorized into three different types: type A (with the small but uniform grain sizes), type B (with the bimodal distribution of grain sizes) and type C (with the large and uniform grain sizes), respectively. The largeness of low-frequency dielectric permittivity at room temperature is closely related to the microstructure. Ceramics with different types of microstructures show the diverse temperature-dependent behaviors of electrical properties. However, the existence of some common characteristics is also found among them. For all of the ceramics, a Debye-type relaxation emerges in the frequency range of 100Hz–100kHz at high measuring temperatures, which has the larger dielectric dispersion strength than the one known in the frequency range above 100kHz. Thus, the high-temperature dielectric dispersion exhibits a large low-frequency response and two Debye-type relaxations. Furthermore, all of the ceramics show three semicircles in the complex impedance plane. These semicircles are considered to represent individually different electrical mechanisms, among which the one in the low-frequency range arises most probably from the contribution of the domain boundaries, and the other two are ascribed to the contributions of the domains and the grain boundaries, respectively.

The electrical properties of CaCu3Ti4O12 ceramic materials, showing an enormously large dielectric constant, were investigated. It was found that the grain boundary plays an important role in the giant dielectric behaviour of these ceramics. Measurement of the electrical current density (J) versus the electrical field (E) was carried out. A good linear relationship between lnJ and E1/2 was found, which demonstrates that the Schottky barrier should exist at the grain boundary. A double Schottky barrier model composed of a depletion layer and a negative charge sheet was proposed, analogous to the barrier model for ZnO varistors. An activation energy value of about 0.6 eV was obtained from the data of the characteristic frequency corresponding to the peak of the imaginary part of the dielectric permittivity versus temperature, which may be attributed to the activation of to in the depletion layer.

We report that the Seebeck coefficient (S) is remarkably enhanced in oxygen-deficient Sr1−xLaxTiO3−δ ceramics. The S values of all oxygen-deficient samples are larger than those of the near-stoichiometric ones and are temperature-independent at high temperatures, showing a narrow band behavior. This indicates that the introduction of oxygen vacancy changes the density of electronic states around the Fermi energy. The maximum for the figure of merit (ZT) of Sr0.9La0.1TiO3−δ ceramic reaches 0.21 at about 750 K, demonstrating enhancement by a factor of more than 1.3 over that of the near-stoichiometric materials.

Developing environmentally friendly lead-free dielectric ceramics with ultrahigh energy storage performance is fundamental to next-generation high-power capacitors but challenging as well. Herein, a record-breaking ultrahigh energy efficiency η of 97.8%...