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Structural transformations and spectroscopic properties of Ni-doped magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2 for broadband near-IR light emission
摘要： Ni:MgAl2O4 spinel shows a reversible random Ni2t site redistribution with increasing temperature. With the aim of determining the influence of the structure evolution induced by heat-treatment on the nature of luminescence centers in NiO-doped spinel-based magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2, the detailed spectroscopic study of the initial glass during its heat-treatments at increasing and decreasing temperatures has been performed and accompanied by an XRD analysis and Raman spectroscopy. The initial glass was X-ray amorphous. Its optical spectrum is mainly formed by absorption of [5]Ni2t sites with a small amount of [4]Ni2t ones. Crystals of the nucleating catalyst, ZrTiO4, about 4 nm in size, appear during heat-treatment at 800 °C, while the absorption spectrum of Ni2t ions remains near unchanged. At 850 °C, spinel crystals with size of about 6 nm precipitate, which is accompanied by a broadband luminescence in the near-IR centered at 1330 nm with a bandwidth of 380 nm. At 950 °C, there is a slight reduction in intensity of absorption bands attributed to [6]Ni2t site redistribution with increasing temperature. A decrease in the amount of the [6]Ni2t luminescent centers is not accompanied by a decrease in the luminescence intensity because of the increased size of spinel crystals. Additional low-temperature heat-treatment does not lead to a redistribution between [6]Ni2t sites in spinel crystals in favor of [6]Ni2t ones. An increase of the luminescence intensity after low-temperature heat-treatment is associated with additional spinel crystallization.
关键词： Glass-ceramics,Luminescence,Spinel,Heat-treatment,Nickel,Absorption
更新于2025-09-23 15:21:21
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Tunable Luminescence Contrast in Photochromic Ceramics (1-x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3:0.002Er by an Electric Field Poling
摘要： A binary solid solution of Er3+ doped (1-x)Na0.5Bi0.5TiO3-xK0.5Na0.5NbO3 (x=0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ferroelectric ceramics has been developed, and a reversible photochromic (PC) reaction and its associated luminescence modulation are realized via alternating the 405-nm light irradiation and thermal stimulation (200 oC). The basic crystal structure, domain structure, ferroelectricity and dielectric behavior of the ceramics were measured. A moderate luminescence contrast ΔRt over 50% is obtained in the fresh samples. Meanwhile, a greatly enhanced luminescence contrast ΔRt is obtained via an electric poling for compositions x=0.02, 0.04, 0.06. For example, ΔRt is promoted from 53.4% to 85.3% for x=0.02. However, the luminescence contrast ΔRt of compositions x=0.08, 0.10, 0.12 is depressed after poling. The mechanisms of enhanced PC reaction and luminescence contrast ΔRt are discussed and proposed. The present study may open a window for enhancing the PC reaction.
关键词： Luminescence modulation,Poling,Ceramics,ferroelectrics,photochromic
更新于2025-09-23 15:21:21
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Electrical Properties and Thermal Expansion Characteristics of (1- <i>x</i> )Ba <sub/>0.948</sub> Ca <sub/>0.05</sub> Er <sub/>0.002</sub> Ti <sub/>0.94</sub> Zr <sub/>0.06</sub> O <sub/>3</sub> -( <i>x</i> )Pr Lead-Free Piezoelectric Ceramics Sintered at a Low-Temperature
摘要： (1 (cid:1) x)Ba0.948Ca0.05Er0.002Ti0.94Zr0.06O3–(x)Pr (x ? 0–0.75 mol%) ceramics are sintered at 1240 (cid:3)C by conventional solid-state reaction method using the as-synthesized nanoparticles, which are prepared by a modified Pechini method. The structural, morphological, electrical, and thermal expansion properties as a function of varying x are systematically investigated. All samples feature rhombohedral phase, and their lattice parameters are accurately calculated by Rietveld refinement software. Volume of oxygen vacancies initially decreases and then increases with increasing x, leading to diversified electrical properties. Deteriorated electrical properties of the ceramics with excessive x are attributed to the increment of defect complexes with a large volume of oxygen vacancies. The coefficient of thermal expansion values of the ceramics that is influenced by phase evolution and structure defects under different temperature ranges are studied. The respective optimal electrical properties, that is, d33 ? 186 pC N mol%. This research is believed to be insightful to practical application of the lead-free multifunctional electron components.
关键词： thermal expansion coefficient,defect complexes,praseodymium-doping,BCEZT ceramics,piezoelectricity
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)] - Design and performance analysis of volumetric solar receiver based on porous foam ceramics
摘要： Volumetric solar receiver is one of three main categories of solar receivers. It has great application prospect due to the simple structure, high thermal efficiency, and the air exit temperature can reach above more than 800℃. The porous material is used instead of tube as absorber in volumetric solar receiver to heat the working medium, and the incident radiation can be absorbed gradually from outside to inside. In this study, an one-dimensional volumetric solar receiver calculating model based on porous foam ceramics is constructed. The temperature distributions and radiation absorption efficiencies at different conditions are analyzed, and a kind of secondary heating volumetric solar receiver is put forward to further improve its thermal efficiency. The results show that both the outlet air temperature and the depth for the temperature of air and ceramic solid reaching to stability decreases apparently with decrease of porosity of ceramic foam, but the temperature of front surface of the receiver increases gradually. With decrease of porous ceramic diameter, the air exit temperature decreases gradually, and the depth for the temperature of air and ceramic solid reaching to stability is decreasing, while, the diameter change has little effect on the temperature of front surface. The air exit temperature increases apparently with decrease of air flow rate and rise of inlet air temperature, and increases with increase of incident radiation intensity. The energy absorbing efficiency is decreasing with decrease of air flow rate and rise of inlet air temperature, and decreases with increase of incident radiation intensity. The presented secondary heating type of receiver can improve the energy absorbing efficiency, although the feasibility and economy of this consideration need further verification in future.
关键词： volumetric solar receiver,porous foam ceramics,temperature distribution,radiation absorption efficiency,secondary heating
更新于2025-09-23 15:21:21
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Fabrication of Laser Grade Yb: Y2O3 Transparent Ceramics with ZrO2 Additive through Hot Isostatic Pressing
摘要： Laser grade 8 at.% Yb: Y2O3 transparent ceramics were fabricated with ZrO2 as a sintering additive by using hot isostatic pressing. The hot isostatic pressed 8 at.% Yb: Y2O3 transparent ceramics have a small average grain size of 3 μm and a high transmittance of 82.8% in the near-infrared light region. Optical homogeneity is compromised slightly in the visible light region likely because of the presence of nano/micro-scaled pores. Laser output at 1076 nm reaches a maximum power of 1.1 W and a slope efficiency of 6.1%, indicating that the hot isostatic pressed 8 at.% Yb: Y2O3 transparent ceramics have a promising optical quality. An unusual laser damage is observed and believed to be related to ZrO2 additive associated defects.
关键词： ZrO2 additive,hot isostatic pressing,laser grade,Yb: Y2O3,transparent ceramics
更新于2025-09-23 15:21:01
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Atomic picture of crack propagation in Li <sub/>2</sub> Oa??2SiO <sub/>2</sub> glassa??ceramics revealed by molecular dynamics simulations
摘要： Fundamental understanding of the interaction between glass and ceramic phases with a running crack and the mechanisms by which propagation is hindered or altered as compared to the precursor parent glasses remains elusive for the lithium disilicate glass-ceramics. We herein conduct extensive molecular dynamics simulations to reveal some atomic details that are otherwise extremely challenging to be probed by experiments. The results show that the crack propagation pathway in glass-ceramics is dramatically different as compared to the precursor parent glass. In glassy sample, clean crack branching seems to be triggered by multiple cavitation events ahead of crack tip. In glass-ceramic samples, however, branching is characterized by microcracks at multiple glass-nanocrystal interface sites, clean nanocrystal cleavage along certain crystalline plane, and even secondary cracks due to the percolation of multiple microcracks. Additionally, the nanocrystal distribution, total volume fraction, and aspect ratio also have pronounced effects on the propagation of a primary crack and can lead to very diverse crack patterns.
关键词： lithium disilicate glass-ceramics,crack branching,microcracks,crack propagation
更新于2025-09-23 15:21:01
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Effect of the Ce3+ concentration on laser-sintered YAG ceramics for white LEDs applications
摘要： This paper describes the laser sintering and luminescence properties of Y3Al5O12 (YAG) phosphors doped with different concentrations of Ce3+ and synthesized using the polymeric precursor method. The ceramics were sintered by a new laser sintering technique in which a CO2 laser is employed as the heating source. The resultant ceramics exhibited a homogeneous microstructure with narrow grain size distribution and high relative density. The introduction of Ce3+ ions led to luminescence quenching at a concentration above 0.5 mol% and a redshift of the emission spectrum band with increasing cerium concentration. The excitation spectrum showed two characteristic bands centered at 340 nm and 460 nm and a relative change in their intensity by change the Ce3+ concentration. The presence of a single valence (Ce3+) of cerium was determined by X-ray absorption near edge structure measurements.
关键词： laser sintering,ceramics,photoluminescence,LED,YAG
更新于2025-09-23 15:21:01
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Increasing Fracture Toughness and Transmittance of Transparent Ceramics using Functional Low-Thermal Expansion Coatings
摘要： Transparent polycrystalline ceramics have the potential to enable applications no other materials can, but to do so their strength and toughness must be improved. However, surface strengthening treatments like those used for glasses have so far remained elusive. Here for the first time, we report on engineering unprecedented surface compression, of the magnitude achieved for ion-exchange strengthened glasses (~750 MPa) in transparent ceramics. This was achieved by applying functional, low thermal-expansion yttria coatings onto yttria-stabilized zirconia substrates and thermally treating. In some instances, the treatment more than doubled the fracture toughness while simultaneously increasing light transmittance.
关键词： surface compression,transparent ceramics,fracture toughness,thermal-expansion mismatch,yttria coatings
更新于2025-09-23 15:21:01
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Deep and high precision cutting of alumina ceramics by picosecond laser
摘要： Ceramics possess high thermal and chemical resistance, low density, and high compressive strength; however, the machining complications imposed by their inherent brittleness limit their range of applications. Laser cutting technology can offer an automated manufacturing technique for machining these brittle materials. In this paper, a laser cutting method, so-called wobbling, was developed for performing deep, high precision, and defect-free laser cutting of industrial grade alumina ceramics. This work explored picosecond laser process parameters such as focal position, linear speed, and wobble amplitude in order to control cut depth and optimize cut quality in terms of kerf width, kerf taper, surface cleanness, while avoiding crack formation. The morphology and cut quality were evaluated using 3D laser scanning microscopy and scanning electron microscopy (SEM). Picosecond laser cutting process parameters were optimized, achieving a maximum material removal rate of ~10 mm3/min. It was shown that the laser cutting process developed via these experiments represents an effective and efficient manufacturing tool that can be incorporated in engineered net shaping systems.
关键词： Laser cutting,Material removal rate,Ablation,Ultrafast laser micromachining,Alumina ceramics
更新于2025-09-23 15:21:01
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Bismuth oxide modified europium and niobium co-doped titanium dioxide ceramics: Colossal permittivity and low dielectric loss design
摘要： Colossal permittivity (CP) materials have many important applications in electronics but their development is generally hindered due to the difficulty in achieving a relatively low dielectric loss. In this work, based on the electron-pinned defect-dipole and internal barrier layer capacitance (IBLC) theory, we designed to add Bi2O3 to (Eu0.5Nb0.5)0.01Ti0.9O2 (ENTO) ceramics to obtain high performance CP materials. The dielectric loss can be reduced down to 0.017 at 1 kHz and room temperature, while the permittivity is kept at a relatively high value (2.7×104). At the same time, the temperature and frequency stability can also be improved. More importantly, the mechanism of decreasing dielectric loss is studied. It is finding that the decrease of dielectric loss is closely associated with the enhanced localized behavior of conduction process at grain boundary. The addition of Bi2O3 can increase the grain boundary resistance and grain-boundary activation energy of the ceramics, which make the conductive behavior of the grain boundaries more difficult, resulting in decreasing the dielectric loss and improve the temperature stability of the ceramics.
关键词： Electronic localization,Bi2O3 modified,Low dielectric loss,TiO2 ceramics
更新于2025-09-23 15:21:01