Measurements of pyroelectric coefficients of BT and BST ceramics

In the work, the field and temperature dependencies on the pyroelectric coefficients of ceramic capacitor structures were measured. Barium titanate (BT) and solid solutions of barium-strontium titanate (BST) were investigate. At temperatures range from 20 °C to 30 °C, the values of the pyroelectric coefficients of the BST ceramics (p) 10-5 - 10-4 C/m2 K exceeded p for the BT ceramics by an order. The developed measurement technique made it possible to carry out direct pyroelectric coefficients measurements and determine the polarization initial state of the samples, regardless of their phase state.

Electrical conduction properties of the BZT–BST ceramics

0.5Ba([Formula: see text][Formula: see text]O3-0.5([Formula: see text][Formula: see text]TiO3 (BZT–BST) has been explored in recent times for potential applications in energy harvesting, electrocaloric and energy storage. To this end, energy harvesting/conversion and storage applications require an understanding of the conduction and loss mechanisms. The conduction mechanism in BZT–BST ceramics is studied using impedance spectroscopy (IS) at 0.1 Hz−3 MHz and 100−600[Formula: see text]C. Impedance study reveals the presence of two types of relaxation processes due to grain and grain boundary contributions. The relaxation time and dc conductivity activation energies are obtained as 1.12/1.3 eV and 1.05/1.2eV for bulk/grain boundary, respectively, and found that oxygen vacancies dominated electrical behavior. The relaxation mechanism follows non-Debye-type behavior. The high resistance of the grain (bulk) in the ferroelectric region does not contribute to the high losses; the losses probably result from the phase transition. Also, BZT–BST ceramics exhibit a negative temperature coefficient of resistance (NTCR) behaviour. From a practical application point of view in the temperature regime of 25–65[Formula: see text]C, the loss’s contribution is low. The significant contributions of loss result from the response of phase-transition in this temperature range (25–65[Formula: see text]C).

Sintering Behavior of BST Nanoparticles at Low Temperature and Electrical Properties of their Ceramics

The powders of the Ba0.75Sr0.25TiO3 (BST) nanoparticles were directly synthesized by milling of Ba(OH)2·8H2O, Sr(OH)2·8H2O and Ti(BuO)4 in ethanol at room temperature. They have homogenous grains of ~15 nm and the high sintering activity. The dense ceramics with the density >90% can be obtained at a sintering temperature of ≤950 oC by them with adding 3 wt% sintering aids of Bi2O3 and Li2CO3. The sintering behavior of the BST nanoparticles by adding the aids of Bi2O3 and Li2CO3 is studied carefully. Several Bi-related compounds are involved in the sintering procedure at a different temperature. They enhance the mass transfer and promote the sintering densification. These compounds such as Ba2BiO4 and SrBiO4 appear at 800 oC, LiBa4Bi3O11 and Sr1.2Bi0.8O3 appear over 830 oC, and Bi8.11Ba0.89O13.05 appears at 950 oC. The cation Bi in the ceramics has mixture valences of 3+ and 5+. It makes the ceramics as semiconducting state with the dark gray color and decreases the ceramics resistivities. With the sintering temperature increase, especially at 950 oC, the cation Bi tends back to single valence of +3 in the ceramics. The most of alkaline earth cations in Bi-related compounds will release and resorb into the lattice of BST and drive the densification of the nanoparticles. The BST ceramics can have a peak dielectric constant >6500 at 53 oC, loss <0.025, and resistivity >1012 W·cm when sintered at a temperature of ≥900 oC with 3 wt% sintering aids. They have a potential application for multiple layer ceramic capacitors (MLCC) with silver inner-electrodes.

Elastic and Anelastic Behavior of Microwave Sintered BCT-BST Ceramics

Lead free 0.55(Ba0.9Ca0.1) TiO3-0.45Ba (Sn0.2Ti0.8) O3 (BCT-BST) ceramic is synthesized by three different techniques viz solid state method, sol-gel method and molten-salt method. The prepared BCT-BST ceramic samples exhibited cubic crystal structure on X-ray powder diffraction analysis. The morphology of the samples is analyzed using transmission electron microscope. The lattice interactions with ultrasonic waves and morphotropic phase boundary at 70oC is confirmed from elastic and anelastic studies of the ceramic. High piezoelectric coefficient d33 of 623 pC/N is achieved in the prepared BCT-BST ceramics.