Minglei Zhao

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.

Dielectric and ferroelectric properties of (Na0.8K0.2)0.5Bi0.5TiO3 thin films prepared by metalorganic solution deposition

(Na0.8K0.2)0.5Bi0.5TiO3 thin films have been prepared on Pt∕TiO2∕SiO2∕Si and p-type Si substrates using a metalorganic solution deposition method. The films annealed at 700 °C crystallize well and present perovskite phase. The films exhibit a well-defined hysteresis loop at an applied voltage of 4 V, with a remanent polarization of 4.7μC∕cm2 and a coercive field of 38kV∕cm. The films also show fatigue-free response up to 1.5×1010 switching cycles. The relaxor behavior of the films is confirmed by the frequency-dependence of capacitance-temperature relation. The capacitance-voltage curves show that the films are polarization-type switching and the memory window is about 2.5 V at ±4V applied dc bias voltages. The changes of dielectric constant and dissipation factor with frequency are also investigated briefly.

Magnetoelectric coupling in nanocrystalline Pb0.82La0.18TiO3

The combined effect of Pb vacancies and La dopant can induce ferromagnetism below 75 K for Pb0.82La0.18TiO3 plates annealed at 700,1000, and 1200 °C for 1 h. Pb0.82La0.18TiO3 plates annealed at 1000 °C for 1 h show the coexistence of ferromagnetism resulting from oxygen vacancies at/near surfaces of nanograins and ferroelectricity near room temperature. Under application of magnetic field, the dielectric constant decreases and the ferroelectric transition temperature shifts to high temperature for Pb0.82La0.18TiO3 multiferroic plates. In addition, the electric field treatment leads to an enormous enhancement of saturation magnetization for Pb0.82La0.18TiO3 multiferroic plates, showing a strong magnetoelectric coupling.

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...

Electric field control of magnetization in Nd1−xSmxFeO3 (x = 0, 0.2, and 0.4) at room temperature

The electric field control of magnetization is observed in Nd1−xSmxFeO3 (x = 0, 0.2, and 0.4) at room temperature. Under the application of electric field, an enhancement of magnetization exists for Nd0.8Sm0.2FeO3, but a decrease of magnetization appears for NdFeO3 and Nd0.6Sm0.4FeO3. The value of magnetization returns again when the applied electric field is removed. Such reversible change of magnetization controlled by electric field at room temperature may be of potential applications in spintronics and data storage technologies with low power consumption.

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.

Room-temperature magnetoelectric coupling in nanocrystalline (Na1−xKx)0.5Bi0.5TiO3 (x = 0.1, 0.16, 0.20, 0.25)

Nanocrystalline (Na1−xKx)0.5Bi0.5TiO3 (x = 0.1, 0.16, 0.20, 0.25) plates exhibit ferromagnetism at room temperature. The reduction of ferromagnetism for the (Na1−xKx)0.5Bi0.5TiO3 plates over time and the high temperature air-annealing indicates that the observed ferromagnetism is connected with the cation vacancies at/near the surface of nanograins. The density functional theory calculation with the local density approximation plus on-site effect method on the magnetism of the (Na5/6K1/6)0.5Bi0.5TiO3 supercell shows that Na vacancies can introduce a nonzero magnetic moment. The (Na1−xKx)0.5Bi0.5TiO3 (x = 0.1, 0.16, 0.20, 0.25) plates when annealed at 900 °C for 1 hour present d0 multiferroicity with the coexistence of ferromagnetism and ferroelectricity at room-temperature. A room-temperature magnetodielectric effect is observed in (Na1−xKx)0.5Bi0.5TiO3 plates and the appropriate substitution of potassium can increase the magnetodielectric effect. In addition, electric field treatment leads to an enormous enhancement of saturation magnetization for (Na1−xKx)0.5Bi0.5TiO3 multiferroic plates, resulting in a strong magnetoelectric coupling.

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.

Enhanced dielectric and piezoelectric properties of Bi5Ti3FeO15 ceramics by manganese doping

Lightly manganese-modified, Aurivillius-type, Bi5Ti3FeO15 (BTF) ceramics were synthesized by substituting a small amount of manganese ions onto the Ti4+ sites using conventional solid-state reaction. The resultant manganese-modified BTF ceramics (BTF-Mn) exhibit better dielectric and piezoelectric properties by comparison with the control BTF. With only 4 mol% manganese substitution, the piezoelectric properties of the BTF-Mn ceramics are optimal, exhibiting a high piezoelectric coefficient (d33~23 pC/N), and a low dielectric loss tanδ (~0.3% at 1 kHz). The temperature-dependent dielectric spectra reveal that the BTF-Mn ceramics possess a high Curie temperature of 765 °C. Such BTF-Mn ceramics also exhibit nearly temperature-independent dielectric properties up to 400 °C, suggesting that the manganese-modified BTF ceramics are promising materials for high temperature piezoelectric applications.