Zhi-Gang Gai

High temperature (NaBi)0.48◻0.04Bi2Nb2O9-based piezoelectric ceramics

The effect of (LiCe) substitution for A site on the properties of (NaBi)0.48◻0.04Bi2Nb2O9 (NB◻N)-based ceramics was investigated. The coercive fields (EC) of NB◻N)-based ceramics were significantly decreased from 61.0to32.5kV∕cm and the Curie temperature (TC) gradually decreases from 820to803°C with increasing the (LiCe) modification. The piezoelectric coefficient d33, planar coupling factor kp, and mechanical quality factor Q of (NaBi)0.38(LiCe)0.05◻0.14Bi2Nb2O9 ceramic were found to be 27pC∕N, 11.2%, and 2600, respectively, together with the high TC (∼809°C) and stable piezoelectric properties, demonstrating that the (LiCe) modified NB◻N-based material a promising candidate for high temperature applications.

Effect of (Li,Ce) doping in Aurivillius phase material Na0.25K0.25Bi2.5Nb2O9

The effect of (Li,Ce) substitution for A site on the properties of Na0.25K0.25Bi2.5Nb2O9-based ceramics was investigated. The piezoelectric activity of Na0.25K0.25Bi2.5Nb2O9-based ceramics is significantly improved by the modification of lithium and cerium. The Curie temperature (TC) gradually increases from 668to684°C with increasing the (Li,Ce) modification. The piezoelectric coefficient d33 of the [(Na0.5K0.5)Bi]0.44(LiCe)0.03[ ]0.03Bi2Nb2O9 ceramic was found to be 28pC∕N, the highest value among the Na0.25K0.25Bi2.5Nb2O9-based ceramics and also almost 50% higher than the reported d33 values of other bismuth layer-structured ferroelectric systems (∼5–19pC∕N). The planar coupling factors kp and kt were found to be 8.0% and 23.0%, together with the high TC (∼670°C) and stable piezoelectric properties, demonstrating that the (Li,Ce) modified Na0.25K0.25Bi2.5Nb2O9-based material a promising candidate for high temperature applications.

Interface-induced piezoelectricity in an unpoled Na0.5Bi0.5TiO3-based composite ceramic

Composite ceramics containing Bi12TiO20 and Na0.5Bi0.5TiO3 grains were fabricated by an ordinary sintering technique. An anomalous piezoelectric response consistent with triclinic symmetry was found in unpoled samples and could be detected up to at least 765 °C. This piezoelectric effect appears concurrently with macroscopic cellular interfaces in as-sintered ceramics, suggesting that it may originate from an interface effect. Since these kinds of composites also have near-zero temperature coefficients of the resonance frequencies over the temperature range from 400 to 520 °C, they have potential as high-temperature piezoelectric materials.

Enhanced piezoelectricity in plastically deformed nearly amorphous Bi12TiO20-BaTiO3 nanocomposites

Bulk Bi12TiO20-BaTiO3 (BTO-BT) nanocomposites are fabricated through the high-temperature interfacial reaction between nanometer-sized BaTiO3 particles and melting Bi12TiO20. Although the obtained BTO-BT nanocomposites are nearly amorphous and display very weak ferroelectricity, they exhibit relatively strong piezoelectricity without undergoing the electrical poling process. The volume fraction of crystalline Bi12TiO20 is reduced to less than 10%, and the piezoelectric constant d33 is enhanced to 13 pC/N. Only the presence of the macroscopic polar amorphous phases can explain this unusual thermal stable piezoelectricity. Combining the results from X-ray diffraction, Raman spectroscopy, and thermal annealing, it can be confirmed that the formation of macroscopic polar amorphous phases is closely related to the inhomogeneous plastic deformation of the amorphous Bi12TiO20 during the sintering process. These results highlight the key role of plastically deformed amorphous Bi12TiO20 in the Bi12TiO20-based pola...

Ultrahigh temperature Bi3Ti0.96Sc0.02Ta0.02NbO9-based piezoelectric ceramics

The effect of (Sc,Ta,Ce) doping on the properties of Bi3TiNbO9 (BTNO)-based ceramics was investigated. The cerium modification greatly improves the piezoelectric activity of Bi3(Ti0.96Sc0.02Ta0.02)NbO9-based ceramics and significantly decreases the dielectric dissipation. The d33 of Bi3Ti0.96Sc0.02Ta0.02NbO9+x wt %CeO2 (x=0.35) was found to be 18 pC/N, the highest value among the BTNO-based ceramics and almost three times as much as the reported d33 values of the pure BTNO ceramics (∼6 pC/N). The modification increased the resistivity ρ of the samples extremely, resolving the low resistivity problem for high temperature applications. The dielectric spectroscopy shows that the TC for all the ceramics is higher than 900 °C. The mechanical quality factor Q and planar coupling factors kp and kt of Bi3Ti0.96Sc0.02Ta0.02NbO9+0.35 wt %CeO2 ceramic were found to be 2835, 9%, and 23%, respectively, and it has high TC and stable piezoelectric properties, demonstrating that the (Sc,Ta,Ce) modified BTNO-based materia...

Piezoelectricity and excellent temperature stability in nonferroelectric Bi12TiO20–CaTiO3 polar composite ceramics

Nonferroelectric Bi12TiO20–CaTiO3 (BT–CT) composite ceramics were prepared through an interfacial reaction between presynthesized crystalline CaTiO3 and crystalline Bi12TiO20 phases at various sintering temperatures. After sintering at temperatures above the melting point of Bi12TiO20, both direct and converse piezoelectric effects were observed in these composites for the first time. Because neither CaTiO3 nor Bi12TiO20 is ferroelectric and because no obvious crystallographic orientation was found in these sintered composites, the temperature gradient-driven plastic flexoelectricity of the grain boundary amorphous phases might be the main poling mechanism. In this work, the highest d33 value of 8 pC N−1 was obtained in the samples sintered at 860 °C, which were found to contain a large amount of amorphous Bi12TiO20 and to possess the lowest density. For these BT–CT polar composite ceramics, the piezoelectric activity, the dielectric loss (tg δ ≈ 0.1%), the mechanical quality factor (Qm ≈ 2300), the depoling temperature (Td ≈ 880 °C) and the temperature stability of the resonance frequency are all comparable to those of the well-known bismuth layer-structured ferroelectrics, which indicates that these new polar composite ceramics are promising candidates for high-temperature piezoelectric applications.

Inhomogeneous crystallinity and its influence on piezoelectricity of Bi12TiO20-BaTiO3 polar composites fabricated by thermal gradient sintering

We have previously described the enhancement of piezoelectricity in low crystallinity Bi12TiO20–BaTiO3 (BTO-BT) nanocomposites. This poses a question regarding the effect of the crystallinity on piezoelectricity. Here, the variation of crystallinity and structure that was developed along the temperature gradient was confirmed. The magnitude of the piezoelectric constant was found to have great relationship with the crystallinity and distortion of BiO5 polyhedra of amorphous Bi12TiO20. The highest piezoelectric constant of 13pC/N was obtained together with the lowest crystallinity and highest degree of distortion of BiO5 polyhedra. These results highlight the key role of the amorphous phase and further confirm the importance of distortion of BiO5 polyhedra in influencing the piezoelectricity. In this view, one may also expect that macroscopic polarity could be improved by increasing the amorphous content and the degree distortion of the BiO5 bonding units in the system.