Analysis of fluorescence properties of novel Eu3+-doped ZnAl2O4-based ceramic aerogels for high-power optical device applications

A novel series of ZnAl₂O₄:Eu³⁺ aerogels (ZAE) and mullite ceramic phase reinforced ZnAl₂O₄:Eu³⁺ aerogels (MZAE) with high fluorescence thermal stability have been firstly synthesized for the encapsulation of high-power optical devices. However, due to the intrinsic structural brittleness of the aerogel, the structure of ZAE tends to collapse during the heat treatment and the fluorescence performance falls short of expectations. To this end, we propose a simple and effective strategy to enhance the structural rigidity of fluorescent aerogels by introducing the mullite ceramic phase into the network structure of ZAE. This can effectively suppress the agglomeration of Eu³⁺ caused by the collapse of the structure during the heat treatment, thus enhancing the optical properties of the aerogel. Compared with ZAE, MZAE has higher fluorescence thermal stability. The fluorescence intensity of MZAE at 498 K is still 75 % of that at 298 K, and the chromaticity shift is only 22 × 10⁻³.     

Preparation,optical, and thermal stability of Tb3+-doped glass ceramics containing Al4Ti2SiO12

The Tb³⁺-doped transparent glass ceramics containing Al₄Ti₂SiO₁₂ crystal are synthesized by the melt-solid-crystallization method. The optimal heat treatment conditions for the glass ceramic samples are determined to be 750°C, 1.5 h based on differential scanning calorimeter, X-ray diffractometer, scanning electron microscope, and light transmittance curve. The luminescence properties of the glass ceramics samples are characterized by a fluorescence spectrometer. The emission spectrum revealed that the dominant emission is green attributed to Tb³⁺, the optimal doping concentration is 0.3%. And the thermal quenching activation energy of 0.3% Tb³⁺-doped glass ceramics is 0.2554 eV, while the relative sensitivity is 1.50% K⁻¹ at 298 K and the absolute sensitivity is 2.27×10⁻² K⁻¹ at 418 K through variable temperature fluorescence spectroscopy test and a series of calculations. These findings demonstrate the excellent stability and temperature sensitivity of glass ceramics, thereby highlighting their potential for use in green lighting and temperature sensing applications.     

(Cu1/3Nb2/3)4+ ionic substituting effects,low-temperature sintering behaviors,and improved temperature stability of Ba3Nb4Ti4O21 microwave dielectric ceramics

In this study, (Cu_1/3Nb_2/3)⁴⁺ complex cation and BaO–ZnO–B₂O₃ glass frit were adopted to solve the high sintering temperature and poor temperature stability of Ba₃Nb₄Ti₄O₂₁ ceramics. It is shown that pure Ba₃Nb₄Ti₄O₂₁ phase was formed when Ti site was partially replaced by (Cu_1/3Nb_2/3)⁴⁺ cation. The increasing number of dopants decreases the dielectric polarizability, correspondingly, the dielectric constant and temperature coefficient of the resonance frequency values are reduced consistently. The variation of the Q × f value is determined by internal ionic packing fraction and external sintering densification. The (Cu_1/3Nb_2/3)⁴⁺ cation effectively decreases the suitable sintering temperature from 1200 to 1050 °C while greatly improving the temperature stability. BaO–ZnO–B₂O₃ glass was used to further improve the low-temperature sintering characteristics of Ba₃Nb₄Ti₄O₂₁ ceramics. It is proven that the addition of glass frits effectively decreases the temperature to 925 °C with combinational excellent microwave dielectric properties: ε_r ～55.6, Q × f ～5700 GHz, τ_f ～3 ppm/^°C, making the Ba₃Nb₄Ti₄O₂₁ ceramics promising in the applications of low-temperature cofired ceramic technology.     

Optimal Nb5+ doping for enhanced optical reflectivity and improved thermophysical properties of La0.9Sr0.1Ti1−xNbxO3+δ

Thermal protection materials with high optical reflectivity, low thermal conductivity, and good high-temperature stability are required for the development of laser technologies and the protection of the critical equipment components. Herein, we synthesize a novel thermal protective material, La_0.9Sr_0.1Ti_1−xNb_xO_3+δ (LSTN; x = 0.1, 0.125, 0.15), with different Nb⁵⁺-ion contents using solid-state sintering. Phase structure analysis demonstrates that LSTN (x = 0.1, 0.125, 0.15) presents a single-phase monoclinic structure with a uniform element distribution. In particular, the LSTN_0.125 ceramic exhibits ultrahigh optical reflectivity (96%, 2300 nm) and excellent thermophysical properties, such as a high thermal expansion coefficient (10.3 × 10⁻⁶ K⁻¹, 1000°C), an ultralow thermal conductivity (0.408 W (m K)⁻¹, 300°C), and excellent high-temperature stability. Aberration-corrected scanning transmission electron microscopy reveals that the disordered substitution of Nb⁵⁺ ions induces numerous lattice distortions and mass fluctuations, which decrease the thermal conductivity, and makes difference in the relative refractive indices of atomic layers causing the high reflectivity of the material. These remarkable properties render the LSTN_0.125 ceramic as an ideal alternative for near-infrared thermal protection applications.     

Spectral Properties of Pr3+‐Doped Transparent‐Glass‐Ceramic Containing Ca5(PO4)3F Nanocrystals

A Pr³⁺‐doped transparent oxyfluoride glass‐ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by melt quenching and subsequent thermal treatment. The crystallization phase and morphology of the Ca₅(PO₄)₃F nanocrystals were investigated by X‐ray diffraction and transmission electron microscope, respectively. The volume fraction of the Ca₅(PO₄)₃F nanocrystals in the glass‐ceramic is about 10% and the fraction of Pr³⁺ ions incorporated into the Ca₅(PO₄)₃F nanocrystals is about 22%. The peak absorption cross sections at 435 and 574 nm increase up to 128% and 132% after crystallization, respectively. The peak stimulated emission cross sections of the ³P₀→³H₄ blue laser channel and ³P₀→³F₂ red laser channel for the glass‐ceramic are 4.95 × 10^?20 and 29.8 × 10^?20 cm², respectively. The spectral properties indicate that the glass‐ceramic is a potential visible laser material.     

Structure,Judd-Ofelt analysis and spectra studies of Sm3+-doped MO-ZnO-B2O3–P2O5 (M = Mg,Ca, Sr,Ba) glasses for reddish-orange light application

In the present work, a series of Sm³⁺-doped MO-ZnO-B₂O₃–P₂O₅ (M = Mg, Ca, Sr, Ba) glasses were prepared. The glass structure and luminescence properties were investigated by XRD, DSC, IR, absorption spectroscopy, Judd-Ofelt theory and photoluminescence spectra. The J-O parameters of Sm³⁺-doped glasses follow the trend of Ω₄＞Ω₆＞Ω₂. Under the excitation of 401 nm Xenon lamp, Sm³⁺-doped glasses exhibited four emissions from the transitions of ⁴G_5/2→⁶H_J/2 (J = 5, 7, 9, 11) in the visible spectra. The luminous intensity of Sm³⁺ increases with the asymmetry in local environments and decreases with the increasing radius of the alkaline-earth cation. Among the as-prepared glass, the Sm³⁺-doped glass containing magnesium oxide exhibits higher values of stimulated emission cross-section (2.18 × 10⁻²¹ cm²), gain bandwidth (1.40 × 10⁻²⁷ cm³), and optical gain (3.83 × 10⁻²⁴ cm²). All the Sm³⁺-doped glasses show intense orange light in the CIE 1931 chromaticity diagram with a high color purity exceeding 99%. In addition, the time-resolved emission spectra reveal the decay process of the Sm³⁺ ions for the transitions ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 in the glass containing magnesium oxide. It suggests that Sm³⁺-doped alkaline-earth zinc borophosphate glasses could be a potential candidate for reddish-orange light-conversion fluorescent materials based on the ultraviolet light-emitting diode.     

High pyroelectric performance in Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3/Al2O3 composites by design

High pyroelectric performance around human body temperature is essential for ultra-sensitive infrared detectors of medical systems. Herein, toward human health monitoring, composite ceramics (1-x)Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.94Ti_0.06]_0.98O₃/xAl₂O₃ (x = 0, 0.1, and 0.2) were designed. A metastable ferroelectric (FE) phase was induced in the anti-FE matrix by the Al₂O₃ component-induced internal stress, and in turn FE-anti-FE phase boundary was constructed. The ceramics at x = 0.2 exhibit high pyroelectric coefficient with p = 10.9 × 10⁻⁴ C·m⁻²·K⁻¹ and figures of merit with current responsivity F_i = 6.23 × 10⁻¹⁰ m·V⁻¹, voltage responsivity F_v = 12.71 × 10⁻² m²·C⁻¹, and detectivity F_d = 7.03 × 10⁻⁵ Pa^−1/2 around human body temperature. Moreover, the enhanced pyroelectric coefficients exist in a broad operation temperature range with a large full width at half maximums of 18.5°C and peak value of 29.2 × 10⁻⁴ C·m⁻²·K⁻¹ at 48.2°C. The designed composite ceramic is a promising candidate for infrared thermal imaging technology of noncontact human health monitoring system.     

Enhanced doping effects of multielement on anisotropic thermal expansion in ZrO2 with new compositions

Coefficient of thermal expansion (CTE) of a solid material plays a critical role for a variety of high temperature applications such as thermal barrier coating (TBC) systems during the thermal cycling process. Ceramics contain ionic bonds; hence they tend to exhibit lower CTE values than alloys/metals. Developing new ceramic thermal barrier materials using promising dopants and compositions that have higher CTE values than the conventional 6-8 wt% Y₂O₃ stabilized ZrO₂(8YSZ) will contribute to the decrease in thermal expansion mismatch between a typical ceramic 8YSZ (10 ~ 11 × 10⁻⁶°C⁻¹) top coat and a metal alloy based bond coat such as NiCrAlY (14 ~ 17×10⁻⁶°C⁻¹, Padture et al., Science, 2002;296:280–4; Liang et al., J Mater Sci Technol, 2011;27(5):408–14), which is highly desirable. This work reports design, modeling, synthesis, and characterization of promising new compositions based on Dy³⁺, Al³⁺, and Ce⁴⁺-doped YSZ that consist of the tetragonal structure and have an enhanced thermal expansion than 8YSZ. The intrinsic CTE at the atomic level has been investigated via molecular dynamics (MD) simulation. The atomic scale analysis provides new insights into the enhanced doping effects of multiple trivalent and tetravalent cations on the lattice structure, lattice energy, and thermal expansion in ZrO₂. The calculated lattice energy becomes smaller with the incorporation of Dy³⁺, Al³⁺, and Ce⁴⁺ions, which corresponds strongly to the increase in CTE. The crystalline size is reduced due to the incorporation of the Al³⁺ and Ce⁴⁺, whereas the sintering resistance is enhanced ascribed to the addition of Dy³⁺ and Al³⁺. Doping Dy³⁺, Al³⁺, and Ce⁴⁺ cations to YSZ increased the CTE value of YSZ and for Dy_0.03Y_0.075Zr_0.895O_1.948, the CTE is 12.494 × 10⁻⁶°C⁻¹ at 900°C, which has an 11% increase, as compared with that of 8YSZ.     

Optical properties of Er3+ and Yb3+/Er3+-doped NaF-Na2SO4-Al(PO3)3 fluoro-sulfo-phosphate glasses

Fluoro-sulfo-phosphate (FPS) glass is of current interest as potential material for laser application due to its good glass-forming ability, thermal, and chemical stability as well as the complicated local environment for incorporated species. Herein, the physical and luminescent properties of Er³⁺ and Yb³⁺/Er³⁺-doped FPS glasses vs S/F ratio are investigated comprehensively. The low melting temperature (750°C) leads to fewer ingredients evaporation and easier operation. The sulfate addition depolymerizes the structure of FPS glasses, leading to either monotonic or nonmonotonic variations of physical properties, while no deterioration in thermal and limited one in chemical stability is caused. The addition of sulfate also modifies the local structure around optical active species and thus, leading to higher emission cross section (1.52 × 10⁻²⁰ cm²), effective linewidth (68.4 nm), figure of merit (5.61 × 10⁻²³ s cm²), gain bandwidth (102.44 × 10⁻²⁷ cm³), and energy-transfer microparameters (51.87 × 10⁻³⁹ cm⁶/s), implying high possibility to serve as 1.5 μm laser application.     

Densification,flexural strength and dielectric properties of CaO-MgO-ZnO-SiO2/Al2O3 glass ceramics for LTCC applications

Novel glass ceramics for LTCC applications with high flexural strength can be achieved by CaO-MgO-ZnO-SiO₂(CMSZ) glass cofiring with Al₂O₃. The sintering shrinkage behavior, crystalline phases, mechanical and dielectric properties, and thermal expansion of the CMZS/Al₂O₃ glass ceramic were determined. The X-ray diffraction results revealed that multiphases (CaMgSi₂O₆, Al₂Ca(SiO₄)₂ and ZnAl₂O₄) formed in the sintering process of the CMZS/Al₂O₃ glass ceramic. The flexural strength of CMZS/Al₂O₃ glass ceramics first increases and then decreases with increasing Al₂O₃ content. The CMZS/Al₂O₃ glass ceramic with 50 wt % Al₂O₃ sintered at 890 °C for 2 h achieved the best performance, with a maximum flexural strength of 256 MPa, dielectric constant (ε_r) of 7.89, dielectric loss (tan δ) of 3.41 × 10⁻³ (12 GHz), temperature coefficient of resonance frequency (τ_f) of −29 ppm/°C, and the CTE value of 7.93 × 10⁻⁶/°C.     

Thermodynamic properties of aluminum titanate-mullite composite ceramics containing heat stabilizer

Using Al₂O₃ and TiO₂ as raw materials, adding MgO as heat stabilizer and mullite as enhancer, aluminum titanate-mullite multiphase ceramics were successfully prepared by solid phase synthesis. The effects of MgO and mullite were systematically studied on the phase composition, microstructure, thermal stability, sintering properties, and mechanical properties of aluminum titanate ceramics. The results showed that the introduction of Mg²⁺ can partially replace Al³⁺ to form Mg_xAl_2(1-x)Ti_(1+x)O₅ solid solution, improved the thermal stability of aluminum titanate ceramics, and promoted the formation and growth of grains, which reduced the sintering temperature. The crack deflections caused by mullite particles improved the mechanical properties. The filling effect of mullite particles and the formation of silica in mullite raw materials were conducive to ceramic densification. The statistics of Mg4M10 sample were as follows: the porosity was only 2.9%, the flexural strength was as high as 64.15 MPa, and the thermal expansion coefficient was 1.35 × 10⁻⁶ K⁻¹ (RT-700°C), encouraging the application of ceramics with high thermal mechanical properties.     

Solidification of glass-ceramics of simulated fission products RE3+, Sr2+, Ba2+ in chlorine-containing waste molten salt

Embedding nuclear waste in glass-ceramic and immobilizing nuclides in ceramic lattice is an effective way for the disposal of high-level radioactive waste. In this paper, a method of solidification of simulated various nuclides was proposed, i.e., RE³⁺(RE = La, Sm, Nd, Dy), Sr²⁺ and Ba²⁺ precipitated from waste molten salt in the form of REPO₄, SrCO₃ and BaCO₃ were solidified in glass-ceramics. To avoid the decomposition of SrCO₃ and BaCO₃ at high temperature, SrCO₃/BaCO₃ containing Cl⁻ salt was further sintered with NH₄H₂PO₄ to form Sr₅(PO₄)₃Cl/Ba₅(PO₄)₃Cl ceramics. It was found that the prepared REPO₄ belonged to monoclinic or tetragonal crystal system, while Sr₅(PO₄)₃Cl and Ba₅(PO₄)₃Cl belonged to hexagonal crystal system. REPO₄, Sr₅(PO₄)₃Cl and Ba₅(PO₄)₃Cl ceramics were co-solidified in iron phosphate glass. BET results showed that the ceramics had a dense structure without any pore inside. XRD, TEM and HRTEM results showed all ceramics had high crystallinity, and nuclides could enter the lattice structure of ceramics through isomorphic replacement, which made the nuclides stable in the crystal structure. The effects of embedding rate on the volume density, Vickers hardness and wettability of glass-ceramics were explored. It was found that the density of the glass-ceramics gradually increased with the increase of ceramic embedding rate, however, the Vickers hardness firstly increased and then decreased. When the embedding rate reached 20 wt%, the Vickers hardness of the glass-ceramics could reach 583.90 GPa. The water contact angles of glass-ceramics with an embedding rate 0–40 wt% were measured to be 70.45°–84.05°, indicating glass-ceramics having a good water leaching resistance. Furthermore, the normalized leaching rate NR_i of La³⁺, Sm³⁺, Nd³⁺, Dy³⁺, Sr²⁺, Ba²⁺, Cl⁻ on the 28th day were estimated to be 7.53 × 10⁻⁷, 5.02 × 10⁻⁷, 5.12 × 10⁻⁷, 4.04 × 10⁻⁷, 1.22 × 10⁻³, 1.59 × 10⁻⁴, 1.07 × 10⁻⁴ g‧m⁻²‧d⁻¹, which indicating that all elements remained good leaching resistance.     

Tailoring the efficient laser-absorption-melting behavior of Bi2O3-B2O3-ZnO-Nd2O3 glass for the OLED encapsulation

The efficient 810 nm laser energy conversion of glass frit had been proven to be the key to the long-term hermetic encapsulation of Organic Light Emitting Display (OLED). A direct laser energy conversion laser-assisted Bi₂O₃-B₂O₃-ZnO-Nd₂O₃ sealing glass material without extra laser absorbent such as carbon black, was designed and systematically investigated. The addition of Nd₂O₃, as glass modifiers with higher cationic field strength, could be conducive to enhancing the polymerization of glass network structure, manifesting that the glass-transition temperature Tg, onset-crystallization temperature Tc and thermal stability ΔT (ΔT = Tc-Tg) increased, while thermal expansion coefficient CTE dropped to 9.72×10⁻⁶/°C and advantageously matched with the glass substrate (8±1×10⁻⁶/°C). More importantly, the absorption rate of BBZ-Nd glass was more than 50 % between 800∼810 nm owing to the 4f-4f electron transition of Nd³⁺ ions, and yet the reflectivity and transmittance of the wavelength at 800–810 nm were lower. As optimal compositions, the addition of 3.0 wt% Nd₂O₃ in Bi₂O₃-B₂O₃-ZnO-Nd₂O₃ glass frit with higher absorption coefficients (80 %) led to instantaneous bonding encapsulation between glass substrates without interfacial cracks or pores with the 808 nm wavelength of the laser at 20 W and 2.4 mm/s.     

Fabrication of double-cladding Ho3+/Tm3+ co-doped Bi2O3–GeO2–Ga2O3–BaF2 glass fiber and its performance in a 2.0-μm laser

A novel double-cladding Ho³⁺/Tm³⁺ co-doped Bi₂O₃–GeO₂–Ga₂O₃–BaF₂ glass fiber, which can be applied to a 2.0-μm infrared laser, was fabricated by a rod-tube drawing method. The thermal properties of the glass were studied by differential scanning calorimetry. It showed good thermal stability and matching thermal expansion coefficient for fiber drawing when T_x−T_g > 193°C and the maximum difference of the thermal expansion coefficient is 3.55 × 10⁻⁶/°C or less. The 2.0-μm luminescence characteristics were studied using the central wavelength of 808 nm pump light excitation. The results show that when the concentration ratio of Ho³⁺/Tm³⁺ reaches 0.5 mol%:1.0 mol%, the maximum fluorescence intensity was obtained in the core glass, the emission cross section reached 10.09 × 10⁻²¹ cm², and the maximum phonon energy was 751 cm⁻¹. In this paper, a continuous laser output with a maximum power of 0.986 W and a wavelength of 2030 nm was obtained using an erbium-doped fiber laser as a pump source in a 0.5 m long Ho³⁺/Tm³⁺ co-doped glass fiber. In short, the results show that Ho³⁺/Tm³⁺ co-doped 36Bi₂O₃–30GeO₂–15Ga₂O₃–10BaF₂–9Na₂O glass fiber has excellent laser properties, and it is an ideal mid-infrared fiber material for a 2.0-μm fiber laser with excellent characteristics     

Negative thermal expansion coefficient of Sc-doped indium tungstate ceramics synthesized by co-precipitation

Co-precipitation was successfully applied to synthesize the Sc³⁺ doped In_2-xSc_x (WO₄)₃ (x = 0, 0.3, 0.6, 0.9 and 1.2) compounds. The composition- and temperature-induced structural phase transition and thermal expansion behaviors of Sc³⁺ doped In₂(WO₄)₃ were investigated. Results indicate that In_2-xSc_x (WO₄)₃ crystalizes in a monoclinic structure at 300 °C for x ≤ 0.3 and changes into hexagonal structure for x ≥ 0.6. Hexagonal In_1.1Sc_0.9(WO₄)₃ displays negative thermal expansion (NTE) with an average linear coefficient of thermal expansion (CTE) of −1.85 × 10⁻⁶ °C ⁻¹. After sintering at 700 °C and above, a phase transition from hexagonal to orthorhombic phase was observed in In_2-xSc_x (WO₄)₃ (x ≥ 0.6). Sc³⁺ doping successfully reduce the temperature-induced phase transition temperature of In_2-xSc_x (WO₄)₃ ceramics from 250 °C (x = 0) to room temperature (x = 0.9). When x = 0.9 and 1.2, the average linear CTEs of In_2-xSc_x (WO₄)₃ ceramics are −5.45 × 10⁻⁶ °C⁻¹ and -4.43 × 10⁻⁶ °C⁻¹ in a wider temperature range of 25–700 °C, respectively.     

Simultaneously enhanced thermal conductivity and dielectric properties of borosilicate glass-based LTCC with AlN and h-BN additions

Microwave devices with reduced dielectric loss and electronic components with increased integration density necessitate the higher performance of electronic packaging materials. The h-BN/AlN/CaCO₃-MgO-B₂O₃-SiO₂-Li₂CO₃ glass composites were prepared via tape-casting and then sintered by pressureless and hot-pressing, respectively. The thermal conductivity of pressureless sintered composite was increased to 6.55 W/(m·K) by incorporating 3 wt% h-BN, and the thermal expansion of 4.47 ppm/K was achieved along with low dielectric constant of 5.76 and dielectric loss of 7.02 × 10⁻⁴ at 24 GHz. In contrast, the hot-pressing sintered composite containing 4 wt% h-BN exhibited higher thermal conductivity of 10.3 W/(m·K) and lower dielectric loss of 4.77 × 10⁻⁴. The microstructure characterization indicated the construction of heat conduction networks, and XRD analysis illustrated the formation of crystallization in the glass. Such low-temperature co-fired ceramic (LTCC) with high thermal conductivity and low dielectric loss would be a promising candidate for electronic packaging and 5G communication applications.     

A novel orange-emitting LaBMoO6:Sm3+ phosphor

Sm³⁺ doped LaBMoO₆ phosphors were prepared by using the solid-state reaction method. The microstructure, morphology, chemical element composition, absorption, luminescent performance, decay life and thermal stability of Sm³⁺ doped LaBMoO₆ samples were studied. Sm³⁺ doped LaBMoO₆ phosphors mainly emit orange light at 596 nm with a decay lifetime of milliseconds under the excitation of 405 nm. The chromaticity coordinates of Sm³⁺ doped LaBMoO₆ samples are located in the orange region, which also have great thermal stability. The Sm³⁺ doped LaBMoO₆ phosphors can be used as orange-emitting materials in W-LED devices.     

Environmental-friendly economical cordierite-mullite-based ceramics for kiln furniture production and supports for CO2 hydrogenation towards C5+ fuels

In this study, lightweight cordierite-mullite ceramics with high strength and high thermal-shock resistance were successfully synthesized by solid-state method with the usage of hollow ceramic microspheres. After careful physico-chemical and mechanical characterization, we gained an economical cordierite material with a low bulk density of 1.40 g/cm³ with an apparent porosity of 44.78%, a flexural strength of 20.17 MPa and a coefficient of thermal expansion of 2.26 × 10^{−6 o}C⁻¹ compared to the bulk counterpart with a bulk density of 2.00 g/cm³ with an apparent porosity of 25.75%, a flexural strength of 23.69 MPa and a coefficient of thermal expansion of 2.47 × 10^{−6 o}C⁻¹. As a catalyst support of Na-FeO_x, the economical cordierite has proved the same stability and activity in CO₂ hydrogenation towards C₅₊ fuels as bulk cordierite-based catalyst counterparts.     

Preparation of environmentally friendly high-emissivity Ca2+-Fe3+ co-doped LaAlO3 ceramic

Ca²⁺-Cr³⁺ co-doped LaAlO₃ is an excellent ceramic material with high emissivity; however, it is harmful to the environment because of the presence of Cr³⁺ ions. In this study, Ca²⁺-Fe³⁺ co-doped LaAlO₃ ceramic materials were successfully prepared via a high-temperature solid-state reaction. The emissivity of Ca²⁺-Fe³⁺ co-doped LaAlO₃ was 0.91, which is approximately equal to that of Ca²⁺-Cr³⁺ co-doped LaAlO₃. To compensate for the lack of data on the thermophysical properties of doped LaAlO₃ high-emissivity ceramics, the thermal expansion coefficients and thermal conductivities of LaAlO₃ doped with Ca²⁺-Fe³⁺ or Ca²⁺-Cr³⁺ were investigated. The thermal conductivities of La_0.9Ca_0.1Al_0.9Fe_0.1O₃ and La_0.9Ca_0.1Al_0.9Cr_0.1O₃ at 1200°C were 3.802 and 3.707 W·m⁻¹·K⁻¹, respectively. The thermal expansion coefficients of La_0.9Ca_0.1Al_0.9Fe_0.1O₃ and La_0.9Ca_0.1Al_0.9Cr_0.1O₃ at 1200°C were 11.49×10⁻⁶ and 11.41×10⁻⁶ K⁻¹, respectively. These results indicate that Ca²⁺-Fe³⁺ co-doped LaAlO₃ exhibits great potential as a new generation of environmentally friendly near-infrared radiating materials in the field of energy efficiency.     

Improved Dielectric and Nonlinear Electrical Properties of Fine‐Grained CaCu3Ti4O12 Ceramics Prepared by a Glycine‐Nitrate Process

Pure CaCu₃Ti₄O₁₂ was successfully prepared by a glycine‐nitrate process using a relatively low calcination temperature and short reaction time of 760°C for 4 h. Fine‐grained CaCu₃Ti₄O₁₂ ceramics with dense microstructure and small grain size were obtained after sintering for 1 h. The nonlinear coefficient of a fine‐grained CaCu₃Ti₄O₁₂ ceramic calculated in the range 1–10 mA/cm² was found to be very high of ~16.39 with high breakdown electric field strength of 1.46 × 10⁴ V/cm. This fine‐grained CaCu₃Ti₄O₁₂ ceramic also exhibited a very low loss tangent of 0.017 at 20°C with temperature stability over the range ?55°C to 85°C. The grain growth rate of the CaCu₃Ti₄O₁₂ ceramics was found to be very fast after increasing the sintering time from 1.5 to 3 h, leading to formation of a coarse‐grained CaCu₃Ti₄O₁₂ ceramic with grain size of about 100–200 μm. The dielectric permittivity of this coarse‐grained ceramic was found to be as high as 1.03 × 10⁵ with a low loss tangent of 0.054.