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Dielectric and piezoelectric properties of Sm3+ doped lead barium niobate (PBN) ceramics
摘要： Rhombohedral samarium doped Lead based ceramic materials were fabricated by a high temperature conventional solid state mixed oxide ceramic process. The ceramic composition Pb1-x-3y/2Bax Re3+ y Nb2O6 (x = 0.35 and y=0.00, 0.02, 0.04 and 0.06, Re3+ = Sm3+). The pure and Sm3+ doped lead barium niobate ceramic materials are single phase with rhombohedral(hexagonal) symmetry obtained from powder x-ray diffraction (XRD). The grain size has been measured for all the compositions and lying between 1.60-2.90μm. Broad dielectric peak phase transitions observed with temperature in pure and Sm3+ ion modified lead barium niobate ceramic materials. It is observed that the high values of piezoelectric charge coefficients in d31 and d33 in Sm3+ doped lead barium niobate ceramics. The mechanical quality factor Qm and d33 increases with increase of Sm3+ ion concentration and indicating a highly polarisable lead ion contributing to high Curie temperature dielectric constant.
关键词： SEM,Piezoelectric properties,Rhombohedral,Synthesis of ceramic compositions,dielectric,X-Ray diffraction
更新于2025-09-23 15:21:21
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Experimental evaluation of volumetric solar absorbers – Ceramic foam vs. an innovative rotary disc absorber concept
摘要： This paper presents the experimental evaluation of two volumetric solar absorber concepts. It compares the thermal performance of conventional foam absorbers with that of an innovative rotary disc absorber design. The moving absorber showed advantages regarding air temperature stability at the outlet and better operability compared to the foam absorber. Unfortunately, it is shown that the innovative rotary disc design in its present form is not competitive, neither in terms of thermal performance, nor regarding mechanical reliability and robustness. The future task is therefore to optimize the mechanical design regarding thermal fatigue, in order to obtain a robust and durable rotary absorber that can be thoroughly evaluated experimentally.
关键词： volumetric solar absorbers,ceramic foam,thermal performance,rotary disc absorber,mechanical reliability
更新于2025-09-23 15:21:21
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Millimetre-wave low-temperature co-fired ceramic bandpass filter with independently controllable dual passbands
摘要： This study presents a detailed investigation on the frequency properties of the stub-loaded stepped-impedance resonator (SIR). For the first time, the frequency controllability of the third and fifth harmonic resonant frequencies (f3 and f5) of the SIR under different ratios of impedance and electric length is subjected to a complete theoretical analysis. It can be found that there is a length ratio which makes f3 and the voltage-null point at f3 never be affected by the change of the impedance ratio. Furthermore, the stub loaded at this voltage-null point also has no effect on f3. These features are successfully applicable to realise independent frequency control for dual-band bandpass filters (BPFs). In this situation, a new coupling path through the loaded stub can be constructed only for f5, and the coupling coefficients for the two bands can be individually varied. Accordingly, both the operational frequencies and bandwidths of the two bands can be separately adjusted. For demonstration, an independently controllable dual-band BPF operating at 27.5/33?GHz is designed and fabricated for millimetre-wave wireless applications. Good accordance is achieved between the simulated and measured results.
关键词： low-temperature co-fired ceramic,independently controllable,bandpass filter,dual passbands,millimetre-wave
更新于2025-09-23 15:21:21
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Eco-friendly highly sensitive transducers based on a new KNN-NTK-FM lead-free piezoelectric ceramic for high-frequency biomedical ultrasonic imaging applications
摘要： High-frequency ultrasonic imaging with improved spatial resolution has gained increasing attention in the field of biomedical imaging. Sensitivity of transducers plays a pivotal role in determining ultrasonic image quality. Conventional ultrasonic transducers are mostly made from lead-based piezoelectric materials that may be harmful to the human body and the environment. In this study, a new (K,Na)NbO3-KTiNbO5-BaZrO3-Fe2O3-MgO (KNN-NTK-FM) lead-free piezoelectric ceramic was utilized in developing eco-friendly transducers for high-frequency biomedical ultrasonic imaging applications. A needle transducer with a small active aperture size of 0.45 × 0.55 mm2 was designed and evaluated. The transducer exhibits great performance with a high center frequency (52.6 MHz), a good electromechanical coupling (keff ~ 0.45), a large bandwidth (64.4% at -6 dB), and a very low two-way insertion loss (10.1 dB). Such high sensitivity is superior to those transducers based on other lead-free piezoelectric materials and can even be comparable to the lead-based ones. Imaging performance of the KNN-NTK-FM needle transducer was analyzed by imaging a wire phantom and an agar tissue-mimicking phantom. Imaging capabilities of the transducer were further demonstrated by ex vivo imaging studies on a porcine eyeball and a rabbit aorta. The results suggest that the KNN-NTK-FM piezoceramic has many attractive properties over other lead-free piezoelectric materials in developing eco-friendly highly sensitive transducers for high-frequency biomedical ultrasonic imaging applications.
关键词： lead-free piezoelectric ceramic,Biomedical ultrasonic imaging,high-frequency ultrasonic transducer,eco-friendly
更新于2025-09-23 15:21:21
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Residual porosity and optical properties of spark plasma sintered transparent polycrystalline cerium-doped YAG
摘要： Transparent cerium-doped yttrium aluminum garnet (Ce:YAG) phosphors are promising candidates for high-power white light emitting diode applications. In the present study, Ce:YAG powder was synthesized by a co-precipitation method and highly transparent ceramics were fabricated by spark plasma sintering. The effects of temperature and pressure, as well as post-sintering treatments (annealing or hot isostatic pressing), on residual porosity were studied by electron and confocal laser microscopy. Correlation between residual porosity characteristics (pore size and volume fraction) and optical properties (in-line transmittance and photoluminescence intensity) of the luminescent transparent ceramics was established.
关键词： Transparency,Spark plasma sintering,Photoluminescence,Ce:YAG ceramic,Residual porosity
更新于2025-09-23 15:21:21
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New Materials for Solar Cells
摘要： Scientists at the Karlsruhe Institute of Technology (KIT) intend to develop a fundamentally new solar cell concept in the project “Innovative liquid-applied ceramic solar cells” (KeraSolar). They combine research on photovoltaics with ceramic functional materials in order to bundle the advantages of different solar cell technologies: The printability of organic solar cells and the long-term stability of crystalline solar cells as well as the ferroelectricity of the lead halide perovskite.
关键词： ceramic functional materials,ceramic solar cells,photovoltaics,KeraSolar
更新于2025-09-23 15:21:01
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YAG:Ce <sup>3+</sup> Transparent Ceramic Phosphors Brighten the Next-Generation Laser-Driven Lighting
摘要： Y3Al5O12:Ce3+ (YAG:Ce3+) transparent ceramic phosphors (TCPs) are regarded as the most promising luminescent converter for laser-driven (LD) lighting. High-quality YAG:Ce3+ TCPs are still urgent for high efficiency LD lighting devices. YAG:Ce3+ TCPs in a vacuum ambience by using nano-sized raw materials are prepared. Controlling defects by adding nano-sized MgO and SiO2 simultaneously enables a high transmittance nearly 80%. After annealing in air furthermore, the luminous efficiency is enhanced greatly from 106 to 223 lm W?1, which is the best result reported now for LD lighting. These results demonstrate that the optimizing YAG:Ce3+ TCPs in a fitting strategy will brighten once again in the next-generation LD lighting. Based on scanning electron microscopy (SEM) coupled with a cathodoluminescence system, defects and Ce3+ distributions in grains are identified directly for the first time.
关键词： cathodoluminescence,laser-driven lighting,transparent ceramic phosphors,Mg2+–Si4+,YAG:Ce3+
更新于2025-09-23 15:21:01
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Enhanced 2???μm Mida??Infrared Laser Output from Tm <sup>3+</sup> a??Activated Glass Ceramic Microcavities
摘要： Transparent glass ceramics (GCs) consisting of an homogeneous glass phase and a well-dispersed crystal phase are considered as ideal optical gain materials potentially applied in optoelectronic devices due to the combination of facile processability of glass and the intense crystal ?eld of nanocrystals. Here, a heat-induced nanocrystal-in-glass method is employed to integrate the active ions Tm3+ into Bi2Te4O11 nanocrystals with an intense crystal ?eld to realize an enhanced microlaser output. This strategy endows the e?cient tellurate GC microcavity laser operating at ≈2 μm. Compared with the laser properties of as-prepared glass microcavities, the pump threshold (260 μW) is as low as less than a quarter and the slope e?ciency (0.0296%) is 5.5 times higher. Furthermore, by carefully engineering the heat treatment temperature and duration, the crystal size and distribution can be precisely controlled. Thus, the Rayleigh scattering loss that is detrimental to quality (Q) factor is e?ectively suppressed and the GC microcavities with high Q factors up to 105 are successfully obtained. This work provides useful insight on the development of optical functional materials and expands the practical applications of GC microcavities in various optoelectronic ?elds.
关键词： mid-infrared lasers,glass-ceramic microspheres,microcavities,whispering gallery mode
更新于2025-09-23 15:21:01
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Femtosecond laser surface engineering of biopolymer ceramic scaffolds coated with ZnO by low temperature atomic layer deposition method
摘要： Surface femtosecond laser texturing of biopolymer and biopolymer/ceramic composites with subsequent ZnO film deposition on the samples by low temperature Atomic Layer Deposition (ALD) method was performed. In the current study, the deposition of ZnO layers was implemented at temperature 50 °C under pressure of 2 mbar. In order to investigate the effect of diverse ZnO thin films thickness, 100 or 500 repeating ALD cycles were applied. The samples were exposed to ultra-short laser pulses of 130 fs duration generated by a CPA (chirped pulse amplifier) Ti:Sapphire laser system. The artificial scaffolds were irradiated by varying the laser fluence (0.2 J/cm2, 0.41 J/cm2 and 2.07 J/cm2) and the number of applied laser pulses (N = 1, 2, 5 and 10). The morphology and chemical properties of the treated samples were evaluated by Scanning Electronic Microscopy, Energy-Dispersive X-ray Spectroscopy and X-ray photoelectron spectroscopy. By combining fs laser modification with low temperature ALD method, essentially improved bioactivity properties of hybrid organic–inorganic bone tissue scaffolds could be achieved, which is of great importance for future tissue engineering application of the samples.
关键词： Atomic layer deposition,Biopolymer/ceramic composites,Femtosecond laser modification,Tissue engineering
更新于2025-09-23 15:21:01
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Monitoring of the Ceramic Kerf During the Laser Cutting Process through Piezoelectric Transducer
摘要： Advanced ceramics are widely used in industry due to their unique properties. However, the machining of ceramic components by conventional methods is difficult due to their high level of hardness and brittleness. In this sense, laser beam machining (LBM) is presented as an alternative to conventional methods, enabling the machining of workpieces through more accurate and less invasive techniques. Despite the advantages of laser machining, the process still needs to be studied in detail, as advanced ceramic machining is considered a stochastic process. Thus, real-time monitoring systems are required in order to optimize the ceramic laser machining. Therefore, this paper proposes a novel method for monitoring the cutting kerf in the laser cutting process of ceramic components using a low-cost piezoelectric transducer (PZT) and digital signal processing. Tests were performed on the surface of an alumina ceramic workpiece under different machining conditions. The cutting kerf was measured by a digital microscope and the raw signals from the PZT transducer were collected at a sampling rate of 2 MHz. Time domain and frequency domain analyses were performed in order to find a frequency band that best correlates with the process conditions. Finally, a linear regression was calculated in order to correlate the PZT signal and the measured kerf. The results showed that the piezoelectric transducer was sensitive to the acoustic activity generated during the process, allowing the real-time monitoring of the cutting kerf. Thus, the approach proposed in this paper can be used efficiently in the monitoring of the laser cutting process.
关键词： monitoring,digital signal processing,ceramic,laser machining,piezoelectric transducer
更新于2025-09-23 15:21:01