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Start Over Author "Li, Lingxia" Publisher elsevier b.v.
255 results on '"Li, Lingxia"'

33. Colossal permittivity in Ta-doped SrTiO3 ceramics induced by interface effects and defect structure: An experimental and theoretical study.

Author

Xue, Keying and Li, Lingxia

Subjects
*DIELECTRIC loss, *PERMITTIVITY, *CERAMICS, *CRYSTAL grain boundaries, *DIELECTRIC properties, *ELECTRIC capacity
Abstract

The lack of systematic research on the phase structure, defect structure, and polarization mechanism hinders the full comprehension of the colossal permittivity (CP) behavior for SrTiO 3 -based ceramics. For this purpose, Ta-doped SrTiO 3 -based ceramics were synthesized in an N 2 atmosphere with a traditional method. When the appropriate amount of Ta was doped, colossal permittivity (ԑ r ∼ 62505), low dielectric loss (tanδ ∼ 0.07), as well as excellent temperature stability (−70 °C–180 °C, ΔC/C 25°C ≤ ±15%) were obtained in the Sr 0.996 Ta 0.004 TiO 3 ceramic. The relationship between Ta doping, polarization mechanism, and dielectric performance was systematically researched according to experimental analysis and theoretical calculations. The first-principle calculations indicate that the Ta5+ ion prefers to replace the Sr-site. The defect dipoles and oxygen vacancies formed by heterogeneous-ion doping play an active role in regulating the dielectric performance of ceramics. In addition, the interface barrier layer capacitance (IBLC) effect associated with semi-conductive grains and insulating grain boundaries is the primary origin of colossal permittivity for Sr 1-x Ta x TiO 3 ceramics. The polarization mechanism and defect structure proposed in the study can be extended to the research of SrTiO 3 CP ceramics. The results have a good development prospect in colossal permittivity (CP) materials. [ABSTRACT FROM AUTHOR]

Published
2023
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43. Developing high-Q × f value MgNb2–xTaxO6(0≤x≤0.8) columbite ceramics and clarifying the impact mechanism of dielectric loss: Crystal structure, Raman vibrations, microstructure, lattice defects, chemical bond...

Author

Li, Lingxia, Li, Yuting, Qiao, Jianli, and Du, Mingkun

Subjects
DIELECTRIC loss, CHEMICAL bonds, CRYSTAL defects, CRYSTAL structure, X-ray photoelectron spectroscopy, SOIL vibration
Abstract

• A strategy to optimize the bond characteristics by introducing Ta5+ is proposed. • Structural properties on MgNb 2− x Ta x O 6 (0 ≤ x ≤ 0.8) solid solutions are clarified. • Considerably enhanced Q × f (∼ 170,000 GHz) is achieved when x = 0.6. • The theory associated with low dielectric loss of MgNb 2 O 6 system is enriched. With the increasing frequency of wireless mobile communication, dielectric materials with higher Q × f are required to enhance the signal strength of microwave passive devices and thus compensate for the rapid attenuation of high-frequency signals during propagation. In order to improve the Q × f of the MgNb 2 O 6 system and study the internal mechanism between the structure and microwave dielectric properties, Ta5+ ion is introduced to design and fabricate MgNb 2− x Ta x O 6 (0 ≤ x ≤ 0.8) ceramics by the solid-state reaction method. The single columbite phase and dense structure are observed throughout the entire composition range. All elements (Mg, Nb, Ta, and O) can be detected by X-ray photoelectron spectroscopy. Insights from the Raman spectroscopy and group theoretical analysis reveal that the A g(2) and A g(3) modes located at ∼ 905 cm−1 dominate the Raman vibration. In addition, the ɛ r depends on the polarizability reflected by the C–M equation and Raman shift. The τ f closely relates to the bond energy of the Nb/Ta–O bond and restoring force characterized by average octahedral distortion of [Nb/TaO 6 ]. Notably, the crucial factors for the huge improvement of Q × f are clarified deeply, in terms of the lower internal strain, the reduced ordering-induced domain size, and the chemical bond valence closer to the ionic valence state, which promotes the stability of crystal structure. Moreover, the introduction of lower electronegative ions enhances the ability of electrons to compensate for oxygen vacancies, thereby reducing the dielectric loss caused by the conductance. Excellent microwave properties (ɛ r = 19.2, Q × f = 170,000 GHz, and τ f = −55.6 ppm °C–1) are achieved in MgNb 1.4 Ta 0.6 O 6 ceramic, specifically a nearly 40% increase in the Q × f. This work has enriched the theory associated with low dielectric loss and provided the MgNb 1.4 Ta 0.6 O 6 ceramic with a pretty high- Q × f for the application in the design of the 5G/6G wireless communication devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Published
2023
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