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Metamaterial emitter for thermophotovoltaics stable up to 1400?°C
摘要： High temperature stable selective emitters can significantly increase efficiency and radiative power in thermophotovoltaic (TPV) systems. However, optical properties of structured emitters reported so far degrade at temperatures approaching 1200 °C due to various degradation mechanisms. We have realized a 1D structured emitter based on a sputtered W-HfO2 layered metamaterial and demonstrated desired band edge spectral properties at 1400 °C. To the best of our knowledge the temperature of 1400 °C is the highest reported for a structured emitter, so far. The spatial confinement and absence of edges stabilizes the W-HfO2 multilayer system to temperatures unprecedented for other nanoscaled W-structures. Only when this confinement is broken W starts to show the well-known self-diffusion behavior transforming to spherical shaped W-islands. We further show that the oxidation of W by atmospheric oxygen could be prevented by reducing the vacuum pressure below 10?5 mbar. When oxidation is mitigated we observe that the 20 nm spatially confined W films survive temperatures up to 1400 °C. The demonstrated thermal stability is limited by grain growth in HfO2, which leads to a rupture of the W-layers, thus, to a degradation of the multilayer system at 1450 °C.
关键词： W-HfO2 layered structure,selective emitters,metamaterial emitter,high temperature stability,thermophotovoltaics
更新于2025-10-22 19:40:53
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Simultaneous realization of broad temperature stability range and outstanding dielectric performance in (Ag+, Ta5+) co–doped TiO2 ceramics
摘要： Effects of sintering condition on dielectric properties and microstructure were systematically investigated in (Ag1/4Ta3/4)0.005Ti0.995O2 ceramics. A giant dielectric constant of ~9831 (1 kHz) and a relatively low dielectric loss of ~0.041 (1 kHz) were realized at the optimal sintering condition of 1330 °C with a holding time for 10 h. Notably, stable temperature coefficient (within -6.8% to 8.8%) of the dielectric constant at 10 kHz was achieved in a broader temperature range (-200–200 °C), which shows superior temperature stability of our sample than the application requirements (-55~200 °C and ?εr/ε25 °C < ±15%) of commercial X9R capacitor.
关键词： sintering conditions,dielectric properties,ceramics,temperature stability
更新于2025-09-23 15:23:52
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Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution
摘要： This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO6 octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi4Ti2.98W0.01Nb0.01O12 possesses an optimum piezoelectric coefficient (d33) of 32 pC/N, a high Tc of 655 °C and a large resistivity of 3 × 106 Ω·cm at 500 °C. The maximum d33 reported here is approximately quadruple than that of pure BIT (~7 pC/N). Moreover, the d33 of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.
关键词： Bi4Ti3O12,Structure distortion,Piezoelectric properties,Oxygen vacancy,Temperature stability
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Love Wave Mode Resonator with a Wide Stable Temperature Range
摘要： One-port Love wave mode resonator has the potential of a wireless sensing platform for measuring physical or chemical parameters because of its sensitivity to mass loading and enhanced sensing areas. Nevertheless, the frequency shift of the sensor due to the working temperature attracts much attention. To design a Love wave mode wireless sensor using one-port resonator with the better temperature compensation characteristics, a layered structure of ZnO/IDT+SiO2/quartz with embedded electrodes is proposed. The amorphous SiO2 is filled in the grooves between the electrodes for temperature compensation on the quartz substrate. Taking account of the third-order nonlinear elastic constants of quartz, ZnO, SiO2 and Al, respectively, a one-port Love wave sensor with relative frequency shift less than 25ppm in the temperature range of 25℃~100℃ is obtained.
关键词： temperature stability,third-order elastic constant,nonlinearity,Love wave resonator
更新于2025-09-23 15:22:29
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Stereo Applications Need a Dedicated Lens Choosing
摘要： Stereo cameras perceive the world in a manner similar to humans; this similarity allows machines using stereo technology to perform and interact like human partners. Robots equipped with a stereo camera can grasp objects autonomously, without the need for additional sensors or lights. Autonomous cars can have the ability to detect a human crossing the street and accurately determine their distance from the moving car, and their walking speed. The selection of the correct lens for a stereo application is much more important than for a setup with a single camera. The position and perspective of each camera with respect to the other determines the system’s accuracy. Environmental parameters require consideration, in addition to temperature, shock, and vibration.
关键词： lens selection,Stereo cameras,shock,temperature,stability,vibration,system environment
更新于2025-09-23 15:21:21
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Improved piezoelectric and strain performance of Na2B4O7-doped (Li,K,Na)NbO3 lead-free piezoceramics
摘要： A polymorphic phase transition effect has been employed to regulate the piezoelectric property of lead-free (K,Na)NbO3-based materials, which intrinsically bear the disadvantage of the evident temperature sensitivity. In this research, Li0.04[(K0.49Na0.51)]0.96NbO3–xNa2B4O7 piezoceramics were prepared through a conventional solid-state reaction. A piezoelectric coefficient d33 of about 285 pC/N and a unipolar strain of 0.14%@5 kV/mm were achieved in the ceramics with x = 0.5%. These improved properties can be ascribed to the coexistence of orthorhombic and tetragonal phase structure around room temperature. Besides, the field-induced unipolar strain varied less than 15% in the temperature region from room temperature to 180 °C. The stability of strain property could be rationally interpreted by a quantitative approach of electrostrictive coupling to the polarization amplitude.
关键词： Piezoelectric coefficient,Lead-free piezoceramics,Temperature stability,Na2B4O7 doping,Polymorphic phase transition
更新于2025-09-23 15:21:01
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In situ TEM observation of controlled growth of two-dimensional WS2 with vertically aligned layers and high-temperature stability
摘要： Layered transition metal dichalcogenides with vertically aligned morphology show great potentials in energy conversion and storage due to the high density of exposed edge sites which have enhanced electrochemical reactivity. In this letter, through in situ heating investigations in a transmission electron microscope, the controlled growth of vertically aligned WS2 with high-temperature stability has been achieved through the thermolysis of solid precursor K2WS4. It is found that the growth of vertically aligned WS2 layers employs hybrid growth modes, in which the growth of new WS2 slab is initiated at old ones from either the middle part or edge part. These vertically aligned WS2 layers show great stability at high temperature of 900°C. Our detailed investigations and theoretical calculations indicate that potassium element in the solid precursor plays a critical role in the growth and evolution of vertically aligned WS2. This method is also applicable to the controlled growth of vertically aligned MoS2 with high-temperature stability through the decomposition of K2MoS4. These findings pave a way for tailored design and fabrication of materials with optimized structure to achieve their superior properties.
关键词： Vertical growth,In situ,High-temperature stability,Transition metal dichalcogenides,TEM
更新于2025-09-16 10:30:52
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Self‐Healable Black Phosphorus Photodetectors
摘要： Large‐strain multilayer actuators (MLAs) were fabricated by tape‐casting 0.91(Na1/2Bi1/2)TiO3–0.06BaTiO3–0.03AgNbO3 (NBT‐BT–3AN) lead‐free incipient piezoceramics co‐fired with Pt inner electrodes. Microstructures, dielectric properties, unipolar and bipolar strain, as well as fatigue properties of the MLAs were investigated. It was found that the actuator consisting of 15 ceramic layers with individual thicknesses of 114 μm could output a large unipolar strain of 0.3% and a dynamic displacement of 5 μm at 6 kV/mm at room temperature. It exhibited excellent cycling stability and provided a high strain of 0.23% after 107 cycles at 6 kV/mm. Moreover, these MLAs still can deliver a strain of 0.20% at 125°C.
关键词： lead‐free piezoceramics,multilayer actuators,large strain,cycling stability,temperature stability
更新于2025-09-11 14:15:04
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Temperature-stable dielectric properties from 100 to 375?°C in system (K0.495Na0.495La0.01)(Nb0.997Cu0.0075)O3–Bi(Mg0.5Zr0.5)O3
摘要： (1-x)(K0.495Na0.495La0.01)(Nb0.997Cu0.0075)O3-xBi(Mg0.5Zr0.5)O3 (abbreviated as KNLNC-xBMZ) ceramics were designed and prepared. The phase transition, microstructure and electrical properties of the ceramics were investigated. The phase structures of the ceramics transform from orthorhombic to pseudocubic phases and the grain sizes decrease gradually with BMZ content (x) increasing. Additionally, BMZ additions can significantly enhance the dielectric temperature stability and decrease the dielectric loss of ceramics over a relatively broad temperature range. KNLNC-0.02BMZ ceramics exhibit high dielectric permittivity (er = 1542) and small variation (Der/er150 (cid:2)C B ± 15%) in dielectric permittivity from 100 to 375 (cid:2)C, and low dielectric loss (tand B 2%) in the temperature range of 100–350 (cid:2)C, which suggests that this ceramic is a candidate for high-temperature capacitor application.
关键词： (K0.5Na0.5)NbO3,Lead-free,Dielectric properties,Elevated temperature stability,Microstructure
更新于2025-09-10 09:29:36
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The effects of terbium oxide on phase transition and electronic properties of potassium-sodium niobate-based ceramics
摘要： Lead free piezoelectric ceramics 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3-xmol%Tb4O7 (KNNS- BNKZ-xTb4O7) are prepared by solid state reaction method. The effects of Tb4O7 on phase transition, grain growth and electronic properties of the ceramics are studied. Tb4O7 (x (cid:1) 0.2) induces a phase transition from tetragonal-orthorhombic coexistence phases to pseudo-cubic one. Meanwhile, Tb4O7 could reduce grain size and lead to step-like grain growth. In addition, Tb4O7 could enhance the temperature stability of KNNS-BNKZ ceramics. For pure KNNS-BNKZ ceramics, the d33* and kp are reduced by 68.0% and 24.3%, respectively, from 30 (cid:3)C to 150 (cid:3)C. For the component x ? 0.1, they are reduced by 6.1% and 1.6%, respectively, in the same temperature range. This paper may have positive signi?cance for searching lead free piezoelectric ceramics with excellent temperature stable properties.
关键词： Piezoelectric ceramics,Phase transition,Lead free,Temperature stability
更新于2025-09-10 09:29:36