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1,283 results on '"Zhou, Zhongxiang"'

360. Enhanced Electrocaloric Effect Induced by the Electric-Field-Generated Like-Multiphase Coexistence in Anisotropic KTa1–xNbxO3Single Crystals

Author

Huang, Xiaolin, Tan, Peng, Wang, Yu, Zhang, Yao, Wen, Xing, Wang, Guanchao, Zhou, Zhongxiang, and Tian, Hao

Abstract

Electrocaloric (EC) refrigeration technologies of ferroelectrics have given rise to significant improvement of environmental problems. Anisotropy of the electrocaloric effect (ECE), as a hopefully effective method to promote EC properties, needs further investigation because of the unclear promotional mechanism of anisotropic domain responses on the ECE. Here, we achieve a significantly enhanced ECE of anisotropic bulk KTa1–xNbxO3(KTN) single crystals and reveal the promotional mechanism of anisotropic ECE induced by switching of different domain structures. The adiabatic temperature change (ΔT) of KTN along the [111]Cdirection is improved by nearly 120% compared with that of KTN along [001]C. Simultaneously, a large EC strength (ΔT/ΔE) of 0.33 K mm kV–1is obtained along the [111]Cdirection under a low driving electric field. Furthermore, we illuminate that the coexistence of like-orthogonal configurations and tetragonal structures induced by the electric field leads to much higher disorder along the [111]Cdirection than the other two directions. Additionally, free energy with triple potential wells is formed because of the like-multiphase coexistence by simulation, which is fundamentally responsible for the larger ΔTof [111]C. The study of revealing the impact on the ECE from anisotropic domain responses provides an effective approach to promote EC performance of ferroelectrics with pronounced anisotropy (perovskites, Aurivillius phase, tungsten bronzes, etc).

Published
2022
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362. A neutron diffraction investigation of high valent doped barium ferrite with wideband tunable microwave absorption

Author

Li, Jun, Hong, Yang, He, San, Li, Weike, Bai, Han, Xia, Yuanhua, Sun, Guangai, and Zhou, Zhongxiang

Abstract

The barium ferrite BaTixFe12−xO19(x= 0.2, 0.4, 0.6, 0.8) (BFTO-x) ceramics doped by Ti4+were synthesized by a modified sol—gel method. The crystal structure and magnetic structure of the samples were determined by neutron diffraction, and confirm that the BFTO-xceramics were high quality single phase with sheet microstructure. With xincreasing from 0.2 to 0.8, the saturation magnetization (Ms) decreases gradually but the change trend of coercivity (Hc) is complex under the synergy of the changed grain size and the magnetic crystal anisotropy field. Relying on the high valence of Ti4+, double resonance peaks are obtained in the curves of the imaginary part of magnetic conductivity (μ″) and the resonance peaks could move toward the low frequency with the increase of x, which facilitate the samples perform an excellent wideband modulation microwave absorption property. In the x= 0.2 sample, the maximum reflection loss (RL) can reach −44.9 dB at the thickness of only 1.8 mm, and the bandwidth could reach 5.28 GHz at 2 mm when RL is less than −10 dB. All the BFTO-xceramics show excellent frequency modulation ability varying from 18 (x= 0.8) to 4 GHz (x= 0.4), which covers 81% of the investigated frequency in microwave absorption field. This work not only implements the tunable of electromagnetic parameters but also broadens the application of high-performance microwave absorption devices.

Published
2022
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363. Electronically controlled flexible terahertz metasurface based on the loss modulation of strontium titanate

Author

Wang, Guanchao, Tian, Hao, Wang, Jing, Li, Shuai, Guo, Wenpeng, and Zhou, Zhongxiang

Abstract

A flexible terahertz metamaterial is designed to control the transmittance through an external electric field. Two different metallic structures, the split ring (type I structure) and the split ring inside a ring (type II structure), were prepared and voltage was applied through a forked finger electrode. The structures were wrapped in a thin film made by mixing strontium titanate nanopowder with polyimide in a certain ratio. Under normal incidence, the transmittance is controlled by applying a voltage to adjust the imaginary part of the permittivity of strontium titanate. The modulation depth of the type I structure at 1.08 THz is 40.1%, and that of the type II structure at 1.16 THz is 44.7%. The working bandwidths of the two structures are 0.07 THz and 0.42 THz, respectively, and are greatly broadened by combining with the ring. The proposed design enriches the modulation method of the transmission of metamaterials and broadens the application range of flexible terahertz metasurfaces.

Published
2022

364. Coaxial double-hole PEDOT: PSS electrodes achieving tunable terahertz zoomable convergence

Author

Li, Shuai, Tian, Hao, Tan, Peng, Wang, Guanchao, Guo, Wenpeng, Wang, Jing, Zhang, Yao, Hu, Chengpeng, Meng, Xiangda, and Zhou, Zhongxiang

Abstract

The local wavefront modulation technique in the terahertz band is an important basis for the development of terahertz modulation technology. Here, an electrically controlled convergent tunable device based on patterned transparent electrode poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) is realized to locally tune the terahertz wavefront. The device consists of two substrates with circular-hole electrodes and liquid crystal sandwiched between them. The refractive index gradient of liquid crystal in the device can be generated by the coaxial double-hole electrodes, which realize continuous control of significant focusing of the terahertz wave. The test results show that the focal length can be modulated in the range of 3–12 cm with varied external voltage; when it varies from 3 to 8 V, the 1/e^2 radius of the spot decreases to 1.3 mm, 0.27 times the initial state, and the spot central intensity magnification increases gradually with the change, up to 3.31 times. The acquisition of the large tunable focal length range of the continuous terahertz zoom device shows that the construction of the gradient refractive index is an important method to regulate the terahertz wavefront by optical means, which greatly promotes the research of terahertz imaging devices.

Published
2021

369. The terahertz characteristics of a sandwich type microplasma structure.

Author

Gao, Ruilin, Yuan, Chengxun, Wang, Ying, Zhou, Zhongxiang, Gong, Dewei, Fang, Yuan, and Rong, Xianwei

Subjects
MICROPLASMAS, FINITE difference method, PERMITTIVITY, METAMATERIALS, COMPOSITE materials
Abstract

Recently, major technical advances in developing intense terahertz (THz) sources have provided us with new opportunities to investigate characteristics of a high density microplasma with THz waves. In this paper, a simple sandwich type microplasma model is established. The finite-difference time-domain method using Z-transforms is utilized to simulate the characteristics of reflection, transmission, and absorption of THz waves in this microplasma structure. The effects of both the microplasma width and the permittivity of the outer medium on the propagation are analyzed, and the results show that the THz waves can be greatly influenced and modulated by the structure of the plasma slab and the outer medium. It is demonstrated that such plasma metamaterials exhibit some extraordinary properties in THz frequency range. [ABSTRACT FROM AUTHOR]

Published
2013
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384. Mechanical control of terahertz plasmon-induced transparency in single/double-layer stretchable metamaterial.

Author

Wang, Jing, Tian, Hao, Wang, Guanchao, Li, Shuai, Guo, Wenpeng, Xing, Juan, Wang, Yu, Li, Li, and Zhou, Zhongxiang

Subjects
TERAHERTZ materials, METAMATERIALS, DEFORMATIONS (Mechanics), POLYDIMETHYLSILOXANE, RESONATORS, RESONANCE
Abstract

Active control of metamaterial properties in stretchable devices is crucial for advanced terahertz (THz) applications, involving large mechanical deformation or stretching. Single/double-layer mechanically tunable THz metamaterial devices based on the polymer polydimethylsiloxane are proposed and experimentally studied herein. The plasmon-induced transparency (PIT) effect is observed in the transmittance spectrum of the single-layer metamaterial, originating from the near-field coupling of two bright modes. Similarly, a bright-dark-coupled PIT system is obtained in the double-layer metamaterial. Furthermore, an external mechanical stretching could exert a switch effect on the sample. The PIT resonances of the single/double-layer metamaterials disappear when the stretching ratio is further increased, as the increased distance between the resonators blocks the coupling effect. The proposed design enriches the approaches to the modulation of the sensitive PIT effect and broadens the applications of stretchable THz equipment. [ABSTRACT FROM AUTHOR]

Published
2021
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385. Control of photorefractive space-charge field and its deflection application in Mn-doped KTa1−xNbxO3 crystal.

Author

Wang, Yu, Tan, Peng, Zhou, Zhongxiang, Huang, Xiaolin, Hu, Chengpeng, Meng, Xiangda, Huang, Fei, Wang, Jing, and Tian, Hao

Subjects
SPACE charge, PHOTOREFRACTIVE effect, OPTICAL devices, SINGLE crystals, REFRACTIVE index
Abstract

The photorefractive effect is an effective way of achieving control of a beam by inducing a space-charge field and controlling the distribution of the refractive index. Herein, the one-dimensional gradient distribution of a space-charge field is structured, and the deflection of the transmitted beam is achieved. The method of regulation and control of the space-charge field was studied by digital holographic microscopy based on a Mn-doped KTN single crystal. The realized deflector has a maximum deflection angle of 0.3° and maintains good frequency-response characteristics up to 50 kHz. This work provides guidance for optical functional devices based on engineering distribution of a space-charge field. [ABSTRACT FROM AUTHOR]

Published
2021
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387. Electro-optic evolution driven by static and relaxational nano ferroelectric domains in KTa1−xNbxO3.

Author

Wang, Yu, Hu, Chengpeng, Tian, Hao, Huang, Fei, Tan, Peng, Wu, Yao, Wang, Chuanzhi, and Zhou, Zhongxiang

Abstract

Polar nano-regions (PNRs), whose evolution and response mechanism are unclear, were identified to be responsible for the pivotal large electro-optic (EO) coefficients near the TC in KTa1−xNbxO3 (KTN) crystals. To investigate this phenomenon, the temperature dependence of its Raman spectrum, and of its linear effective and quadratic EO coefficients, were investigated. Our results showed that both the relaxational nano-domains driven by biased electric fields under ordered static domains and strong anisotropy determined by the deformation of the NbO6/TaO6 realize enhancements of EO properties in the vicinity of Tf. We expect this understanding of the dynamic EO characteristics to be valuable for developing photonic devices and for providing a basis for exploring the origin of giant EO and piezoelectric effects in disordered ferroelectrics and relaxors. [ABSTRACT FROM AUTHOR]

Published
2020
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397. LD pumped 1347 nm laser with a novel Nd:GdNbO4 crystal

Author

Yan, Renpeng, primary, Zhao, Chuang, additional, Li, Xudong, additional, Yu, Xin, additional, Liu, Zhixiang, additional, Wen, Xiaolin, additional, Yao, Wenming, additional, Gao, Jing, additional, Peng, Fang, additional, Zhang, Qingli, additional, Dou, Renqin, additional, and Zhou, Zhongxiang, additional

Published
2018
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