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Fused silica ceramic has become one of the most widely used radome materials in the world since the 1970s. But its poor mechanical properties restricted its application to some extent. To improve the mechanical properties of the fused silica ceramic and keep its characteristic for radome materials, silicon nitride (Si3N4) whisker‐reinforced fused silica ceramics were prepared by a slip‐casting method in the work. The influence of Si3N4 whisker contents on the properties of the slurry was studied, indicating that the preferable pH values of the slurry were 4–6 and whisker contents were 10 wt.%. The flexural strength of as‐prepared Si3N4w/SiO2 ceramic was about 74.35 MPa, exhibiting an increase of 7.75% over that of the pure silica sample. Its dielectric constant in the range from 8 to 12 GHz and tanδ under 10 GHz were, respectively, 3.37 and.0011. It is of great interest to find that Si3N4w/SiO2 has excellent oxidization resistance and its mass maintains even at 1270°C. [ABSTRACT FROM AUTHOR]

High temperature piezoelectric materials have attracted much attention owing to their potential applications for structural health monitoring and nondestructive evaluation in new jet engines, steam and nuclear plants. Nonstoichiometric (Na 0.5- x Bi 0.5+ x )Bi 2 Nb 2 O 9 high temperature piezoceramics were prepared by a conventional solid-state sintering route. The microstructure, dielectric, DC resistivity and piezoelectric properties were investigated. Pure Aurivillius phase structure only existed in a narrow region (−0.02 ≤ x < 0.02). Moreover, the anisotropic grain morphologies were significantly restrained by increasing Bi contents. The oxygen vacancies were artificially tailored in nonstoichiometric compositions. The dynamic piezoelectricity as a function of the poling electric field was also studied and underlying physic mechanism was discussed. (Na 0.48 Bi 0.52 )Bi 2 Nb 2 O 9 ceramic has the large piezoelectric coefficient ( d 33 ∼20.8pC/N), high Curie-temperature ( T C ∼796 °C) and low thermal aging rate (<10% @700 °C), indicating that it is a promising candidate for ultra-high temperature piezoelectric sensor applications. [ABSTRACT FROM AUTHOR]

(Li, Ce, La) multi-doped Na 0.5 Bi 2.5 Nb 2 O 9 ceramics were prepared by a conventional solid state sintering method. Microstructure of sintered ceramics was examined by the X-ray diffraction and scanning electron microscopy. The introduction of voluminous La 3+ cations decreases the degree of lattice distortion, leading a lower Curie-temperature. The detailed electrical conduction behaviors were determined by the electrochemical impedance spectra (EIS). The electrical properties were investigated as a function of frequency (10 2 –10 6 Hz) at various temperatures (350–750 °C). The underlying physical mechanism of electrical properties at high temperature for multi-rare-earth doping NBN-based was studied via an assistance of EIS techniques. There were a set of Debye-like relaxation peaks in the imaginary part of impedance and electric modulus data. Oxygen vacancies are responsible for both ac conduction and dielectric relaxation processes. A discontinuous variation of the exponent parameter n is found owing to a ferroelectric-ferroelastic phase transition around 550 °C. [ABSTRACT FROM AUTHOR]

Aurivillius phase Bi 3 Ti 1− x Ta x Nb 1− x W x O 12 high temperature piezoceramics were prepared by a conventional solid state reaction method. The crystal structure, dielectric, electrical conduction and piezoelectric properties were systematically studied. Pure or modified Bi 3 TiNbO 9 ceramics revealed the presence of only two-layered Aurivillius phase, indicating that Ta/W doping entered into the B-site of pseudo-perovskite structure and formed solid solutions. The Curie temperature had a strong reliance on the structural distortion. Furthermore, Ta/W dopants act as a donor doping, decrease the number of oxygen vacancies and facilitate the domain wall motion. As a result, Ta/W modifications significantly increase the DC resistivity and piezoelectric properties. Bi 3 Ti 0.98 Ta 0.02 Nb 0.98 W 0.02 O 12 ceramics possess the optimum d 33 value (∼12.5 pC/N) together with a high T C point (∼893 °C). Moreover, the resonance–antiresonance spectra demonstrate that the Ta/W-BTN ceramics are indeed piezoelectric in nature at 600 °C. The d 33 value of BTTNW-2 ceramic remains ∼12.2 pC/N after annealing at 700 °C. These factors suggest that the BTTNW-based ceramic is a promising candidate for ultra-high temperature sensor applications. [ABSTRACT FROM AUTHOR]

• Lanthanide doped CBN-based ceramics were prepared. • Lattice distortion and microstructure were influenced by the dopants. • Ce-CBN ceramics exhibit some unique electrical properties. • The variation of piezoelectric and resistance refers to the oxygen vacancies induced by Ce-doping. Calcium bismuth niobate (CaBi 2 Nb 2 O 9 , CBN) is a promising candidate for high-temperature applications in aerospace, shipping, and nuclear industries, owing to its ultra-high Curie temperature (T C ∼x223C 940 °C). Lanthanide ions modified CBN based ceramics were prepared by a conventional solid-state sintering route. The crystal structure, microstructure, and high-temperature electrical properties of CBN ceramics doped by different lanthanide dopants (La, Ce, Nd, Sm, Dy, Er, Yb) were studied and the underlying mechanism was also discussed. Among these doping ions, Ce3+/Ce4+ doping CBN ceramics exhibits anomalous electrical properties. Impedance analysis was introduced to clarify the difference in electrical properties of lanthanide-doped CBN ceramics at high temperatures. As a result, the anomalous electrical properties are attributed to the extrinsic oxygen vacancies induced by the Ce doping. These results could assist to tailor the electrical properties of Aurivillius phase ceramics with lanthanide modifications. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] W/Ni codped BIT ceramics were sintered at low temperature. [•] W dopants decrease the degree of lattice distortion. [•] The increasing resistivity is attributed to alleviation of underbonding of Bi ions. [•] Oxygen vacancy is responsible for dielectric dispersion and DC electrical conduction. [•] The ferroelectricity of BITWN-12 ceramic was systematically studied. [ABSTRACT FROM AUTHOR]

Highlights: [•] K+ modified LNN-based ceramics were synthesized by using mixed oxide routes. [•] K+ ions induced a phase transition from orthorhombic to tetragonal structure. [•] Dielectric behavior above T C was discussed and followed the Curie–Weiss law. [•] A set of material constants were determined by using a resonance–antiresonance method. [•] K+ dopants make a ‘softening’ effect on LNKNS-based piezoceramics. [ABSTRACT FROM AUTHOR]

Abstract: Aurivillius type (NaBi)0.5−x (LiCe) x Bi2Nb2O9 ceramics were prepared by the standard ceramics route. The single crystal structural ceramics were achieved for all compositions and lattice distortion was decreased by (LiCe) dopants. The temperature dependent dielectric properties revealed that all compositions possess a high Curie-temperature (>780 °C). A modified Curie–Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition indicating the degree of diffuseness of NBN-based ceramics increased with (LiCe) modifications. The degradation of resistance implied a plausible model that Ce4+ ions entered into the B-site of the pseudo-perovskite structure and acted as acceptor doping. Further investigation demonstrated that both electrical conduction and dielectric relaxation processes were associated with the oxygen vacancies produced by the substitution of Nb5+ ions by the Ce4+ ions. [Copyright &y& Elsevier]

Abstract: (Na0.25K0.25Bi0.5)1− x (LiCe) x /2[] x /2Bi4Ti4O15 (NKBTLC-x) ceramics were prepared using the conventional solid state sintering method. X-ray diffraction results demonstrated that all samples have a single four-layered Aurivillius-type structure and the lattice distortion increases with increasing x, which induces the variation of Curie temperature (T C). Dielectric and electrical properties have been carried out over a wide range of frequency (100Hz–1MHz) and temperature (450–750°C) in order to elucidate the basic mechanism on the conduction and relaxation process. The relaxation process was explained by thermal activated hopping mechanism and shows an anomaly around the T C, temperature dependence of ac conductivity can be separated into three regions and the activation energy E a was calculated from the Arrhenius law. Moreover, the behavior of ac conductivity as a function of frequency was obeyed the universal power law and attributed to hopping conduction mechanism. [Copyright &y& Elsevier]

Different type doped CaBi 2 Nb 2 O 9 (CBN) ceramics were prepared by a conventional solid state sintering method. The number of oxygen vacancies were decreased or increased by the introduction of W 6+ and Ti 4+ doping in CBN ceramics. The influence of W 6+ , Ti 4+ and W 6+ /Ti 4+ dopants on the microstructures and electrical properties of CBN-based ceramics was investigated. The voids and spherical morphology in the SEM image of W, Ti co-doped ceramics indicate that W, Ti co-doping could change the microstructure of CBN-based ceramics. Impedance analysis results show that the electrical properties of CBN-based ceramics have a close relationship with the number of oxygen vacancies. W doping and W, Ti co-doping decrease the oxygen vacancies, as a result, the resistance and piezoelectric properties were increased and the frequency dispersion of dielectric properties were restrained. [ABSTRACT FROM AUTHOR]

Sintering temperatures (1050–1150 °C) play an important role on influencing microstructures and electrical properties of Bi 4 Ti 2.95 W 0.05 O 12.05 + 0.2 wt%Cr 2 O 3 ceramics. Firstly, the lattice constants and relative density of samples varied with sintering temperatures. And the increase in sintering temperatures increased their grain size and decreased the porosity, resulting in the extreme grain growth of the sample sintered at 1150 °C. Based on these structural evolutions, ϵ r , TK ϵ and tan δ of samples deceased with the increase in sintering temperatures, while T c , d 33 and k p increased with it. ρ dc of samples also increased with the increase in sintering temperatures below 1125 °C, but decreased sharply at 1150 °C. The variation in 2 E c of samples with sintering temperatures may be related to the 90° domain walls. The sample sintered at 1150 °C presented a lower ρ dc due to the high aspect ratio, but possessed a higher d 33 due to the large grain size. [ABSTRACT FROM AUTHOR]