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: <i>Ab initio</i> lattice dynamical perspective
摘要： The hydration and ammonization of ZrW2O8 is known to lead to positive and negative thermal expansion behavior, respectively. We report ab initio calculations to understand this anomalous behavior. We identify the crucial low-energy phonon modes involving translations, rotations, and distortions of WO4 and ZrO6 polyhedra, which lead to negative thermal expansion in ZrW2O8 in pure and ammoniated forms; however, the rotation and distortion motions get inhibited on hydration and lead to positive thermal expansion. We demonstrate that the thermal expansion coef?cient could be tailored by engineering the phonon dynamics of a material.
关键词： ZrW2O8,hydration,phonon dynamics,ab initio calculations,ammonization,thermal expansion
更新于2025-09-04 15:30:14
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Active Thermal Control of 5 nm Gap Terahertz Antennas
摘要： Metallic nanostructures are combined with various active materials for electrical, optical, and thermal modulations of their optical properties. In particular, for the thermal modulation, deformation of metallic nanostructures at high temperatures limits the applications to relatively low temperatures, where thermal expansion of metals is negligible. Here, a unique regime is reported where terahertz (THz) waves transmitting through 5 nm wide slot antennas can be significantly modulated via controlled thermal expansion of metals without active materials. The normalized amplitude is modulated by 20% and the resonant frequency by 22% at an elevated temperature of 150 °C, indicating a decrease in the gap width by 50%. The extreme width-to-length ratio of the THz slot antennas compensates the small thermal expansion coefficient of metals, enabling the gap width to be considerably changed. COMSOL simulation and coupled-mode method (CMM) calculation quantitatively support the experimental data. This works suggests a new possibility of thermally active metallic nanostructures.
关键词： metamaterials,active modulation,terahertz spectroscopy,nanogaps,thermal expansion
更新于2025-09-04 15:30:14
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Measurement of the thermal expansion coefficient of Guadua angustifolia-Kunth using the photoacoustic technique
摘要： In this paper, the Linear Thermal Expansion Coefficient of Guadua angustifolia–Kunth samples was measured using the Photoacoustic (PA) technique in a heat transmission configuration and considering the thermoelastic bending as a PA signal generation mechanism in addition to the thermodiffusion ones. The obtained value of (27±7)×10-6K-1 is a reasonable value compared with that reported for similar materials such as wood.
关键词： photoacoustic technique,thermal expansion coefficient,Guadua angustifolia-Kunth
更新于2025-09-04 15:30:14
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Strain-Mediated Substrate Effect on the Dielectric and Ferroelectric Response of Potassium Sodium Niobate Thin Films
摘要： If piezoelectric thin films sensors based on K0.5Na0.5NbO3 (KNN) are to achieve commercialization, it is critical to optimize the film performance using low-cost scalable processing and substrates. Here, sol–gel derived KNN thin films are deposited using a solution with 5% of potassium excess on Pt/TiO2/SiO2/Si and Pt/SrTiO3 substrates, and rapid thermal annealed at 750 ?C for 5 min. Despite an identical film morphology and thickness of ~335 nm, an in-plane stress/strain state is found to be tensile for KNN films on Pt/TiO2/SiO2/Si, and compressive for those on Pt/SrTiO3 substrates, being related to thermal expansion mismatch between the substrate and the film. Correspondingly, KNN films under in-plane compressive stress possess superior dielectric permittivity and polarization in the parallel-plate-capacitor geometry.
关键词： stress/strain,ferroelectric hysteresis,dielectric properties,KNN thin films,sol–gel,thermal expansion
更新于2025-09-04 15:30:14
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Análise da expans?o térmica volumétrica e das características estruturais de solu??es sólidas de (Pb, Ca)TiO3 entre 150 e 570 K
摘要： Ceramic samples of lead modified calcium titanate (Pb1-xCaxTiO3) with calcium concentration between 0.24≤x≤0.55 were prepared and analyzed in order to determine the structural origin of the negative thermal expansion observed in this ferroelectric system. The Rietveld structural refinement method was used to assess the thermal evolution of the structural parameters using powder X-ray diffraction data collected between 150 and 570 K. Since the Pb1-xCaxTiO3 phase diagram and space groups are still unknown for the temperature range investigated, the structural analyses were based on adjustments of the refinement protocol. The results revealed the existence of a correlation between symmetry transitions and anomalies in the thermal expansion of the unit cell, being such transitions not necessarily of the ferroelectric-paraelectric nature.
关键词： Rietveld refinement method,symmetry transitions,structural analyses,unit cell thermal expansion,ferroelectric ceramics
更新于2025-09-04 15:30:14
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[ASME ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering - Madrid, Spain (Sunday 17 June 2018)] Volume 11B: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering - Investigation on Temperature Compensation of Fiber Bragg Grating Sensors for Hull Monitoring
摘要： Hull monitoring system with Fiber Bragg Grating (FBG) sensors increasingly receives people's attentions. However, for the ship hull monitoring, the deformation of hull girder changes a lot as is subjected to a huge temperature variation. Therefore, the compensation method with only FBG temperature self-correction is not suitable for the hull monitoring sensors because no material thermal expansion effects are reasonably included. In this paper, the new compensation method of hull monitoring FBG sensor based on the sensor theory with both FBG temperature self-correction and steel thermal expansion effects correction is studied. The coupled compensation method suitable for hull monitoring sensor is obtained by theoretical derivation. As the comparison, the coupled compensation experiment was carried out. The results show that the relative error under the temperature compensation method is large in the case of drastic strain and temperature changes, and the correction results of the tested method will be closer to the true level.
关键词： temperature compensation,coupled compensation method,steel thermal expansion,hull monitoring,Fiber Bragg Grating (FBG) sensors
更新于2025-09-04 15:30:14