Narrow Results

A relaxor electroceramic $0.35\mathrm{\text{Pb}}({\mathrm{\text{Mg}}}_{1/3}{\mathrm{\text{Nb}}}_{2/3}){\mathrm{\text{O}}}_3$–$0.35({\mathrm{\text{Pb}}}_{1-1.5x}{\mathrm{\text{La}}}_x){\mathrm{\text{TiO}}}_3$–0.30-$({\mathrm{\text{Ba}}}_{1-1.5x}{\mathrm{\text{La}}}_x){\mathrm{\text{TiO}}}_3$ (PMN–PLT–BLT) with $x$ = 0.25, 0.50 and 0.75 was synthesized using the two combination methods of auto-combination and hot-pressing. Characterization of the crystal phase, microstructure, optical and dielectric properties of PMN–PLT–BLT was made primarily by X-ray diffraction and TEM and SEM methods. The pure perovskite crystals (rhombohedral and tetragonal) prepared at $850^{\circ }\mathrm{\text{C}}$ for 2 h calcination were revealed by using X-ray diffraction. The average optical transmittance of these electroceramics in the range between 450 nm and 900 nm is higher than 60% while in the IR region reached 100%. The PMN–PLT–BLT with $x$ = 0.75 displays the highest transparency around 70% near 1100 nm. The microstructures and dielectric measurements show that these three electroceramics have densities of about 98.8% and exhibit a normal relaxation characteristic.

The comparative analysis of the dielectric properties of bismuth-containing pyrochlores with different manifestation of atomic order/disorder was carried out. We examined the dielectric properties (including behavior in electric fields) of two pyrochlore compounds: BZN (presumably a composition close to ${\text{Bi}}_{1.5}$${\text{Zn}}_{0.5}$${\text{Nb}}_{1.5}$${\text{O}}_{6.5})$ ceramics with chemical disorder in both A and B cation sublattices and Bi₂Ti₂O₇ single crystal with fully chemical ordered structure. The fundamental differences between the dielectric properties of the BZN ceramics and Bi₂Ti₂O₇ single crystal were shown. In particular, in the dielectric relaxation behavior (which cannot be described via Arrhenius law in the Bi₂Ti₂${\text{O}}_7)$ or in the influence of the electric fields on the dielectric permittivity (splitting of the field-cooled and zero-field-cooled behaviors was observed for Bi₂Ti₂O₇ below estimated freezing temperature). The results of this study highlights the special role of Bi₂Ti₂O₇ as a candidate material for studying aspects of geometric frustration related with pyrochlore structure in non-magnetic medium and specifies the future directions of research.

With the increasing demand of high-power and pulsed power electronic devices, environmental-friendly potassium sodium niobate ((Na${}_{0.5}$K${}_{0.5}$)NbO₃, KNN) ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density ($W_{\mathrm{\text{rec}}}$). Nevertheless, the dielectric loss also increases as the external electric field increases, which will generate much dissipated energy and raise the temperature of ceramic capacitors. Thus, an effective strategy is proposed to enhance the energy storage efficiency ($\eta$) via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na${}_{0.5}$K${}_{0.5}$)-NbO₃–0.1Bi(Zn${}_{2/3}$(Nb${}_x$Ta${}_{1-x}$)${}_{1/3}$)O₃ ceramics. On the one hand, the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short–range polar nanoregions (PNRs), resulting in the high $\eta$. On the other hand, the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the $E_{\mathrm{\text{b}}}$. As a result, high $W_{\mathrm{\text{rec}}}$ of 3.29 J/cm³ and ultrahigh $\eta$ of 90.1% at the high external electric field of 310 kV/cm are achieved in $x$ = 0.5 sample. These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.