Preparation and characterization of lithium ion-conducting glass-ceramics in the Li1 + xCrxGe2 − x(PO4)3 system

Li₂O–Cr₂O₃–GeO₂–P₂O₅ based glasses were synthesized by a conventional melt-quenching method and successfully converted into glass-ceramics through heat treatment. Experimental results of DTA, XRD, ac impedance techniques and FESEM indicated that Li_1.4Cr_0.4Ge_1.6(PO₄)₃ glass-ceramics treated at 900 °C for 12 h in the Li_1 + xCr_xGe_2 − x(PO₄)₃ (x = 0–0.8) system exhibited the best glass stability against crystallization and the highest ambient conductivity value of 6.81 × 10⁻⁴ S/cm with an activation energy as low as 26.9 kJ/mol. In addition, the Li_1.4Cr_0.4Ge_1.6(PO₄)₃ glass-ceramics displayed good chemical stability against lithium metal at room temperature. The good thermal and chemical stability, excellent conducting property, easy preparation and low cost make it promising to be used as solid-state electrolytes for all-solid-state lithium batteries.     

Synthesis and characterization of tin containing molybdophosphate and tungstophosphate glasses

Two series of tin containing molybdophosphate and tungstophosphate glasses and glass-ceramics were achieved by means of a domestic microwave oven under air. During melting, a redox reaction takes place between Sn²⁺ and Mo⁶⁺ generating the crystallization of a Na(Sn^IV,Mo^IV)(PO₄)₃ solid solution with a NZP (NaZr₂P₃O₁₂) type structure. Such reactivity was not underlined in the case of the W-series. All the samples were characterized from a thermal and mechanical point of view as a function of the RO₃ (R = Mo, W) for SnO substitution. Two types of behaviors were identified. For the Mo-series, all the characteristics, except density, present an extremum value for the chemical composition with a 1:1 SnO-MoO₃ molar ratio. This is strongly correlated to the amount of NZP crystals present in the glass ceramic, the different behavior observed for the density being due to the low compactness of the NZP phase. For the W-series, all these different characteristics varies monotonously according to a progressive strengthening of the network by replacement of a low field strength ion (Sn²⁺) by a higher field strength ion (W⁶⁺). In addition, the solid state reactivity of a 1:1 SnO-RO₃ mixture was examined confirming the absence of any redox process between SnO and WO₃ during the glass synthesis.     

Bulk crystallisation of (00l) oriented fresnoite Sr2TiSi2O8 in glass-ceramics of the Sr-Ti-Si-K-B-O system

This paper shows that glass-ceramics containing highly surface and bulk preferentially oriented fresnoite Sr₂TiSi₂O₈ crystals can be synthesised by a simple isothermal heat treatment of suitable glass compositions in the Sr-Ti-Si-K-B-O system. For all tested compositions, crystallisation starts from the free surfaces of the specimens and propagates to bulk with time. If most of these compositions lead to (00l) preferential orientation at the specimens' surfaces, bulk crystal texture is very composition dependent. The effects of variation in K₂O and B₂O₃ contents on the crystallisation have been studied. It is shown that low K₂O and high B₂O₃ contents are required to keep the (00l) orientation from the surface into the bulk. This result seems to be explained by the viscosities of the initial and residual glasses at the temperature of crystallisation: a low viscosity leads to a fine and homogeneous microstructure with small and strongly (00l) bulk oriented crystals.     

Broadband infrared luminescence of Ni-doped silicate glass-ceramics containing lithium aluminate spinel nanocrystals

Transparent Ni²⁺-doped SiO₂-Al₂O₃-Ga₂O₃-Li₂O (LGAS) glass-ceramics embedding lithium aluminate spinel nanocrystals was prepared. After heat treatment, LiAl₅O₈ crystallite was precipitated in the glasses, and its size was about 3 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-made glass to the octahedral sites in the glass-ceramics. Upon excitation at 980 nm, broadband infrared luminescence centered at around 1250 nm with full width at half maximum (FWHM) more than 250 nm was observed originating from the ³T₂(³F) → ³A₂(³F) transition of Ni²⁺ in octahedral sites. The broadband near-infrared (NIR) emission from Ni²⁺-doped glass-ceramics can be as host materials for broadband optical amplifier.     

Melt-casting of Si-Al-Y-O glasses and glass-ceramics by combustion synthesis under high gravity

Si-Al-Y-O glasses and glass-ceramics were prepared via melt-casting by combustion synthesis under high gravity. The phase assemblage and microstructure of the cast products strongly depended on the content of SiO₂ and the additive ZrO₂ or La₂O₃ in the starting compositions. With increasing content of SiO₂, the glass-forming ability of the melt was enhanced. The additive ZrO₂ was not dissolved into the glass and inclined to crystallize, but La₂O₃ was inclined to remain in the glass matrix instead of precipitation. With a short processing period and lower energy consumption, combustion synthesis under high gravity can offer a new approach to fast fabrication of glass and glass-ceramic materials.     

Effect of frit size on sintering, crystallization and electrical properties of wollastonite glass-ceramics

Wollastonite glass-ceramics were prepared through pressureless sintering. The sinterability of the prepared samples of the glassy powder in the system (SiO₂-CaO-Na₂O-Fe₂O₃-WO₃) was investigated in the temperature range 720-900 °C and soaking time of 180 min. The influence of the increase in the glass powder particle size on the sinterability and dielectric properties of the glass-ceramic samples was studied.The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. XRD analysis revealed that wollastonite was the main crystalline phase in the sintered glass-ceramics. Dielectric properties such as dielectric constant and dielectric loss were measured via a network analyzer at 10 GHz.It was observed that the increase of the glassy powder particle size improved the sinterability and dielectric properties of the glass-ceramic specimens. Wollastonite glass-ceramics with 16 μm particle size had maximum constant and minimum loss (ε_r = 10.10 and tan δ = 0.005) compared with the other glass-ceramics.     

铈掺杂钆镓铝石榴石相玻璃陶瓷的光学及光谱参数

根据X射线衍射图谱对铈掺杂的钆镓铝石榴石相玻璃陶瓷的晶体结构进行分析,采用直径10英寸积分球结合CCD(charge coupled device)探测器系统,对蓝色半导体发光二极管激发下铈掺杂钆镓铝石榴石相玻璃陶瓷的荧光光谱进行测试,解析出样品发光的绝对光谱功率分布,推导出光量子数分布,求得荧光量子产率和组合白光的色坐标及其相关色温。结果表明,所调查的铈掺杂钆镓铝石榴石相玻璃陶瓷在蓝光LED激发下的荧光量子产率为29.2%,所获得组合白光的色坐标x=0.319,y=0.349,相关色温为6 086K。尽管该混晶陶瓷的荧光量子产率稍小于铈掺杂YAG玻璃陶瓷,但其与蓝光LED组合后发光的色温也明显低于后者,从而为舒适型LED照明玻璃陶瓷的进一步优化提供了新思路。     

Features of the local structural disorder in Li2O-CaF2-P2O5 glass-ceramics with Cr2O3 as nucleating agent

Li₂O-CaF₂-P₂O₅ glasses mixed with different concentrations of Cr₂O₃ (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy (EDS), differential thermal analysis and conventional spectroscopic techniques. The X-ray diffraction and scanning electron microscopic studies reveal the presence of lithium phosphate, calcium phosphate and chromium phosphate (complexes of Cr³⁺, Cr⁵⁺ and Cr⁶⁺ ions) crystal phases. The study on DTA suggests that the crystallization is predominantly due to the surface crystallization when the concentration of nucleating agent Cr₂O₃ is around 0.8 mol%. The IR and Raman spectral studies of these samples indicate that the sample crystallized with 0.8 mol% Cr₂O₃ is more compact and possesses high rigidity due to the presence of chromium ions largely in tetrahedral positions.     

Structure,crystallization and dielectric resonances in 2–13 GHz of waste-derived glass-ceramic

Structure, kinetics of crystallization, and dielectric resonances of waste-derived glass-ceramic prepared via quench-heating route were studied as a function of dosage of iron ore tailing (IOT) within 20–40 wt% using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and vector network analyzer (VNA) measurements. The glass-ceramic mainly consisted of ferrite crystals embedded in borosilicate glass matrix. Crystallization kinetics and morphologies of ferrite crystals as well as coordination transformation of boron between [BO₄] and [BO₃] in glass network were adjustable by changing the amount of IOT. Dielectric resonances in 6–13 GHz were found to be dominated by oscillations of Ca²⁺ cations in glass network with [SiO₄] units on their neighboring sites. Ni²⁺ ions made a small contribution to those resonances. Diopside formed when IOT exceeded 35 wt%, which led to weakening of the resonances.     

MAS-NMR study of lithium zinc silicate glasses and glass-ceramics with various ZnO content

Lithium zinc silicate glasses of composition (mol%): 17.5Li₂O-(72−x)SiO₂-xZnO−5.1Na₂O−1.3P₂O₅−4.1B₂O₃, 5.5?x?17.7, were prepared by conventional melt-quenched technique and converted to glass-ceramic by controlled crystallization process. ²⁹Si and ³¹P MAS-NMR was used to characterize the structure of both glass and glass-ceramic samples. Despite the complex glass composition, Q², Q³ and Q⁴ sites are identified from ²⁹Si MAS-NMR, which relative intensities are found to vary with the ZnO content, indicating a network depolymerization by ZnO. Moreover, well separated Q³ and Q⁴ resonances for low ZnO content indicates the occurrence of phase separation. From ³¹P MAS-NMR, it is seen that phosphorus is mainly present in the form of ortho-(Q⁰) and pyro-phosphate (Q¹) structural units and variation of ZnO content did not have much effect on these resonances, which provides an additional evidence for phase separation in the glass. On conversion to glass-ceramics, lithium disilicate (Li₂Si₂O₅), lithium zinc ortho-silicate (Li₃Zn_0.5SiO₄), tridymite (SiO₂) and cristobalite (SiO₂) were identified as major silicate crystalline phases. Using ²⁹Si MAS-NMR, quantification of these silicate crystalline phases is carried out and correlated with the ZnO content in the glass-ceramics samples. In addition, ³¹P spectra unambiguously revealed the presence of crystalline Li₃PO₄ and (Na,Li)₃PO₄ in the glass-ceramics.