Enhanced up-conversion luminescence of Tb3+-Yb3+ doped glass ceramics by doping Li+

Tb³⁺-Yb³⁺ co-doped transparent glass ceramics (GCs) containing Y₂Ti₂O₇ crystal phases were synthesized by the melt crystallization. The light transmittance of GCs in the visible region reached 78%, and the average grain size was 278 nm under the optimal heat treatment conditions (720 °C/2 h). The GCs exhibited greater up-conversion luminescence intensity than precursor glass, and the reason for this result was explained in accordance with the Judd-Ofelt theory. Moreover, the introduction of Li⁺ did not change the crystalline phase of GCs. The emission intensity of the green light of the 8% Li ⁺ doped GCs was significantly enhanced by nearly 4.48 times under 980 nm excitation. The XRD refinement results suggest that the enhanced luminescence intensity is correlated with the change of the Y₂Ti₂O₇ crystal lattice caused by Li⁺ doping. The relevant luminescence mechanism was elucidated. The results suggest that Li⁺ doped transparent GCs open novel avenues for green UC applications.     

Effect of MgO addition on the crystallization and in vitro bioactivity of glass ceramics in the CaO–MgO–SiO2–P2O5 system

CaO–MgO–SiO₂–P₂O₅ glass ceramics were successfully prepared by sintering the sol–gel-derived powders. The effects of MgO addition on the samples crystallization and structure were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, samples degradation and in vitro bioactivity assays were also evaluated. With more MgO addition, the glass ceramics crystallization kinetics under non-isothermal conditions changed from bulk crystallization to surface crystallization, and new crystal phases of Ca₂MgSi₂O₇ and SiO₂ were induced. In addition, it is observed that with increasing MgO concentration, the glass ceramics degradability gradually decreased and the formation of apatite was delayed.     

First La2O2S infrared transparent ceramics

Lanthanum oxysulfide (La₂O₂S) was investigated as infrared transparent ceramic to benefit from stronger chemical bonds and superior mechanical performances to that of non-oxide benchmark infrared materials. La₂O₂S ceramics were processed by hot-pressing powders prepared by combustion synthesis followed by a sulfurization treatment. Powders and ceramics were characterised through various techniques (XRD, UV-Vis-IR spectroscopy, particle size analysis, SEM, Impulse Excitation Technique, microhardness and fracture toughness tests) to assess their purity, study their microstructure and determine their optical and mechanical properties. The study reports the first IR transmission spectra, Poisson’s ratio, Young’s and shear moduli and fracture toughness values of La₂O₂S polycrystalline ceramics. The ceramics showed transparency in the 2–11 µm range and their mechanical performances were all superior to that of commercial infrared ceramics. The best transmission (89% of the theoretical transmission) was measured at 7.3 µm for 1 mm-thick ceramics hot-pressed at 1200–1250 °C.     

Structural,physicomechanical, and in vitro biodegradation studies on Sr-doped bioactive ceramic

This study aimed to investigate the effect of Sr substitution on the structure, mechanical properties, bioactivity, and biodegradation of akermanite (Ca₂MgSi₂O₇). Samples were synthesized through solid-state synthesis followed by heat treatment at 1200 °C and 1250 °C. X-ray diffraction patterns showed that Sr substitution did not change the Ca₂MgSi₂O₇ phase. Fourier transform infrared spectra demonstrated that the silicate structure of Ca₂MgSi₂O₇ also remained unchanged. The field emission scanning electron microscopy revealed that partial Sr substitution enhanced the density of Ca₂MgSi₂O₇ and reduced the grain size. The optimum dopant with the highest mechanical properties was 0.05Sr. However, the mechanical properties decreased beyond 0.05Sr because of the large grain size. The mechanical properties of Sr-substituted samples sintered at 1250 °C were lower due to high liquid phase formation. Sr substitution supported apatite formation and controlled Ca₂MgSi₂O₇ degradation after the samples were soaked in simulated body fluid solution (SBF).     

Effect of applied pressure on microstructure and properties of hot-pressed Ca-doped LaCrO3 ceramics

High-density chromium deficient calcium-doped lanthanum chromite-based ceramics (La_0.8Ca_0.2Cr_0.98O₃) were prepared by hot pressing (HP) at different sintering pressures, and the highest density can reach 98.8%. The effects of sintering pressure on the microstructure, mechanical properties, and electrical conductivity of La_0.8Ca_0.2Cr_0.98O₃ materials were studied. The experimental results show that HP can increase the density of lanthanum chromite-based ceramic materials and significantly inhibit the growth of grain size. As the sintering pressure increases, the strength and hardness gradually increase, but the fracture toughness decreases. When the sintering pressure is greater than 58 MPa, the presence of the second phase CaCr₂O₄ can be detected in the XRD results of the sintered ceramics. The SEM results showed that CaCr₂O₄ had two completely different morphologies in the sintered ceramics, and it was initially speculated that the possible causes were due to two different generation pathways. The electrical conductivity decreases with increasing sintering pressure, whereas the maximum electrical conductivity obtained is 18.61 S/cm in vacuum at 800°C for pressureless sintering ceramic.     

Crystallization behavior,microstructure and dielectric properties of lead titanate glass ceramics in the presence of Bi2O3 as a nucleating agent

The crystallization behavior of PbO–TiO₂–B₂O₃–SiO₂ glasses in the presence of Bi₂O₃ as a nucleating agent were studied utilizing XRD, DTA, SEM. The glass samples heat treated in the range of 557–630 °C for different soaking times, all developed PbTiO₃ (PT) with perovskite structure. It was found that the addition of 0.5–1.0 mol% Bi₂O₃ resulted in the formation of homogenous, nano-structured glass ceramics with a mean crystallite size of 20–25 nm and PbTiO₃ as the major crystalline phase. The dielectric constant and dissipation factors for the prepared glass ceramics were in ～140–400 and ～0.04–0.4 ranges respectively.     

Isothermal phase diagram of CaO–SiO2–Nb2O5–La2O3 system at 1300 °C and 1200 °C

Thermodynamic properties of CaO–SiO₂–Nb₂O₅–La₂O₃ slag system are of great significance for the utilization and application of niobium and rare earth resources. In the present work, the phase equilibria in CaO–SiO₂–Nb₂O₅–La₂O₃ system at 1300 °C and 1200 °C have been experimentally investigated. A total of 12 equilibrium phase regions have been determined in the constructed isothermal spatial phase diagram, including five four-phase regions: Liquid + SiO₂+CaNb₂O₆+LaNbO₄, Liquid + CaNb₂O₆+Ca₂Nb₂O₇+LaNbO₄, Liquid + Ca₂Nb₂O₇+CaO·3SiO₂·2La₂O₃+LaNbO₄, Liquid +10CaO·6SiO₂·Nb₂O₅+Ca₂Nb₂O₇+LaNbO₄, Liquid + LaNbO₄+SiO₂+CaO·3SiO₂·2La₂O₃; six three-phase regions: Liquid + SiO₂+LaNbO₄, Liquid + CaNb₂O₆+LaNbO₄, Liquid + Ca₂Nb₂O₇+LaNbO₄, Liquid + CaO·3SiO₂·2La₂O₃+Ca₂Nb₂O₇, L + CaNb₂O₆+Ca₂Nb₂O₇, Liquid + SiO₂+CaNb₂O₆; four two-phase regions: Liquid + SiO₂, Liquid + CaNb₂O₆, Liquid + LaNbO₄, Liquid + Ca₂Nb₂O₇. Subsequently, the isothermal section of CaO–SiO₂–Nb₂O₅-(5%, 10%, 15%, 20%, 25%, 30%) La₂O₃ pseudo-ternary systems have been obtained.     

Structure Evolution and Enhanced Microwave Dielectric Characteristics of (Sr1−xCax)La2Al2O7 Ceramics

(Sr_1?xCa_x)La₂Al₂O₇ (0.1 ≤ x ≤ 0.5) ceramics were prepared by a standard solid‐state reaction method. Their densification behavior and microwave dielectric properties were investigated together with the structural evolution. X‐ray diffraction analysis indicated that the major phase of Ruddlesden–Popper structure with n = 2 was obtained for all the compositions investigated here. Partial Ca substitution improved the sintering behavior of SrLa₂Al₂O₇ ceramics. More importantly, microwave dielectric characteristics were enhanced in (Sr_1?xCa_x)La₂Al₂O₇ ceramics with compositions of x = 0.1~0.3. The stacking fault was confirmed by TEM observation in the present ceramics, and the microwave dielectric loss was influenced by it. The best combination of microwave dielectric characteristics was achieved for the composition of x = 0.1: ε_r = 19.9, Qf = 135 400 GHz and τ_f = ?18.5 ppm/°C.     

Pyrochlore glass-ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization

Pyrochlore glass-ceramics (GCs) have been investigated with samples fabricated via both sintering and hot isostatic pressing (HIPing) of a mixed oxide precursor. It has been demonstrated that sintering at 1200°C in air is necessary to obtain well-crystallized pyrochlore crystals in a sodium aluminoborosilicate glass through a one-step controlled cooling. The crystallization, structure, and microstructure of Eu₂Ti₂O₇ pyrochlore as the major phases in residual glass were confirmed with X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy, transmission electron microscopy, and Raman spectroscopy. The structures of major Eu₂Ti₂O₇ pyrochlore and minor [Eu_4.67O(SiO₄)₃] apatite in both sintered and HIPed samples were refined using synchrotron XRD data. While the processing atmosphere did not appear to affect the cell parameter of the main pyrochlore phase, very small volume expansion (~0.3%) was observed for the minor apatite phase in the HIPed sample. In addition, static leaching of the HIPed sample confirmed that pyrochlore GCs are chemically durable. Overall, pyrochlore GCs prepared via both sintering and HIPing with the Eu partitioning factor of ~23 between ceramics and the residual glass are suitable waste forms for minor actinides with processing chemicals.     

Persistent luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics processed by aerodynamic levitation

Glass beads of the Sr₂MgSi₂O₇ stoichiometric composition and a non-stoichiometric composition with higher SiO₂/SrO ratio doped with Eu₂O₃/Dy₂O₃ were prepared through aerodynamic levitation coupled to CO₂ laser heating. The glass beads were subsequently treated at 1100 ºC to produce glass-ceramics with Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ as the main crystalline phase. The doped glasses exhibit red emissions; after crystallisation, the corresponding glass-ceramics emit blue light under UV excitation. The starting glass composition considerably affects the crystallisation process, resulting in Sr₂MgSi₂O₇ glass-ceramics with very different microstructures which, in turn, have a significant influence on the luminescence properties. The photoluminescence emission spectra of the glass-ceramics under UV light show a broadband emission (λ = 400–500 nm) with a main peak assigned to the typical Eu²⁺ transition under excitation at 365 nm. Both the intensity of the emission and the persistence time significatively increase on decreasing temperature. Glass-ceramics from the non-stoichimetric glass composition co-doped with 1Eu₂O₃/0.5Dy₂O₃ (mol%.) provided the longest persistence times.     

Structural Optimization and Improved Discharged Energy Density for Niobate Glass‐Ceramics by La2O3 Addition

The structural and dielectric properties were investigated in the La₂O₃ added glass‐ceramics based on complex niobates. With the addition of La₂O₃, the optimization of microstructure was observed which resulted in the improvement of breakdown strength for the glass‐ceramics. Besides, the dielectric constant was drastically enhanced because of the doping effect of La³⁺ in the A‐sites of both crystallographic structures. Due to the combined effects of both high breakdown strength and polarization difference, the maximum discharged energy density of 1.2 J/cm³ was achieved in the niobate glass‐ceramics with 2 mol% La₂O₃, suggesting dielectric glass‐ceramics of this composition could be the most attractive candidate for high‐energy density capacitors.     

High-performance B4C-LaB6 composite ceramics fabricated via hot-pressing sintering with La2O3 as sintering additive

The B₄C-LaB₆ composite ceramics were fabricated via hot-pressing sintering at 2050 °C and 20 MPa pressure with the mixture of boron carbide (B₄C) and 2–5 wt% lanthanum oxides (La₂O₃) as raw materials. The effects of additive La₂O₃ content on the microstructures and mechanical properties of composite ceramics were investigated, and reaction mechanisms of La₂O₃ and B₄C at different temperatures were studied in detail. La₂CO₅, La₃BO₆ and LaBO₃ were formed by the reactions of La₂O₃ and B₄C at different temperatures, and finally LaB₆ was formed below 1600 °C. The comprehensive mechanical properties of B₄C-LaB₆ composite ceramics were optimized by adding 4 wt% La₂O₃, the flexural strength, fracture toughness and Vickers hardness reached 350 MPa,4.92 MP am^1/2 and 39.08 GPa, respectively. The high densification and flexural strength of composite ceramics achieved in the present study were attributed to LaB₆ hindering the movement of grain boundary. However, the densification was reduced caused by CO as La₂O₃ content increased to 5 wt%. The fast channel was formed via B₄C reacting with La₂O₃, which accelerated migration of B₄C in the sintering process. The content of La₂O₃ played an important role in the fracture mode of the composite ceramics, and ultimately affected the fracture toughness of the composite ceramics.     

Achieving ultrafast discharge speed and excellent energy storage efficiency in environmentally friendly niobate-based glass ceramics

Environmentally friendly Na₂O–BaO–Nb₂O₅–SiO₂ glass ceramics (GCs) with different vanadium pentoxide (V₂O₅) contents were successfully synthesized using the conventional melt-quenching method and heat treatment. The microstructure and dielectric energy storage properties of the GCs could be related to the addition of V₂O₅. When 1 mol% of V₂O₅ was added_, the activation energy of crystallization decreased from 282 to 221 kJ/mol, and the GCs had the highest energy efficiency of 95.96% and breakdown strength of 1326 kV/cm. Moreover, the GCs could also achieve an ultrafast discharge time of 14 ns and an actual discharge energy density of 0.724 J/cm³. These results indicate that these environmentally friendly GCs can be used in energy storage devices.     

The transition from non-ohmic to ohmic characteristics in La2O3 doped ZnO–MgO–TiO2 linear resistance ceramics

La₂O₃ doped ZnO–MgO–TiO₂ based linear resistance ceramics were prepared by the solid phase sintering method. The doping content of La₂O₃ is from 0.0 wt% to 2.5 wt%. The solubility of La₂O₃ in ZnO is less than 0.06 mol% (0.5 wt%), La_0.66TiO_2.993 phases will be formed at grain boundary and change the distribution of spinel phase when La₂O₃ is excessive. For I–V test, undoped sample exhibits typical non-ohmic characteristics, but La-doped samples show excellent ohmic behaviors under low DC and high pulse current (PC). The complex impedance spectrum and the frequency dependent conductivity furtherly demonstrate that La-doped samples possess linear characteristics because there is no grain boundary effect which can affect the electron transmission at grain boundaries. Besides, the decrease of the grain boundary barrier from 0.2135eV for undoped sample to 0.0031eV for 0.5 wt% La doped samples can account for the elimination or reduction of grain boundary effect. In this work, the transition from non-ohmic to ohmic properties by doping La₂O₃ in ZnO–MgO–TiO₂ multiphase ceramics is realized.     

Effect of MgO/La2O3 additives on sintering behavior and microwave dielectric properties of (Sr,Ca)TiO3-(Sm,Nd)AlO3 ceramics

The effect of MgO/La₂O₃ additives on phase composition, microstructures, sintering behavior, and microwave dielectric properties of 0.7(Sr_0.01Ca_0.99)TiO₃−0.3(Sm_0.75Nd_0.25)AlO₃ (7SCT-3SNA) ceramics prepared via conventional solid-state route were systematically investigated. MgO/La₂O₃ as additives showed no obvious influence on the phase composition of the 7SCT-3SNA ceramics and all the samples exhibited pure perovskite structures. The presence of MgO/La₂O₃ additives effectively reduced the sintering temperature of 7SCT-3SNA ceramics due to the formation of a liquid phase at a relatively low temperature during sintering progress. The 0.5 wt% MgO doped 7SCT-3SNA sample with 0.5 wt% of La₂O₃, sintered at 1320 °C for 4 h, was measured to show superior microwave dielectric properties, with an ε_r of 45.57, a Q×f value of 46205 GHz (at 5.5 GHz), and τ_f value of −0.32 ppm/°C, which showed dense and uniform microstructure as well as well-developed grain growth.     

The influence of MgO on the crystallization behaviour and properties of SrO-rich phosphosilicate glasses

A series of glass was produced to investigate the effect of MgO/SrO replacement on the crystallization characteristics and properties of phosphosilicate glasses containing high SrO content. The glass samples were synthesized by conventional melting technique based on 5CaO-(40-X)SrO-X MgO– 43SiO₂–7P₂O₅–5CaF₂ (where; X = 10, 20, 30 and 40 mol%). The influence of MgO/SrO replacement on phase assemblages, microcrystalline structures, thermal expansion, and mechanical properties was examined as a function of basic chemical compositions and crystallization parameters. Predominant strontium meta-silicates together with strontium fluoroapatite phases are crystallized from the base glass free of magnesium. The substitution of strontium by magnesium up to 50% led to formation strontium akermanite phase Sr₂MgSi₂O₇ at the expense of SrSiO₃ phase. Whereas the increase of the MgO/SrO of more than 50%, which led to the crystallization of the clino-enstatite MgSiO₃ as a predominant phase. The results show that the α-values of the glass-ceramics are ranged in 94–125 × 10⁻⁶ K⁻¹ over the temperature range (25–500 °C). On the other hand, MgO/SrO replacements led to enhancing the microhardness of the resultant crystalline materials from 4713 Mpa to 6744 Mpa. As a result of the designed glass compositions, promising crystalline phases were obtained as well as good thermal and mechanical properties for the resultant glass-ceramics. Therefore, the designed glass-ceramics can be strongly used as biomaterials especially for bone reconstruction applications.     

Development of a new glass–ceramic by means of controlled vitrification and crystallisation of inorganic wastes from urban incineration

This paper reports the results of a study of the feasibility of recycling the solid residues from domiciliary waste incineration by producing a glass-ceramic. The major components of the raw material (TIRME F+L), which was from a Spanish domiciliary incinerator, were CaO, SiO₂ and Al₂O₃ but nucleating agents, such as TiO₂, P₂O₅, and Fe₂O₃ were also present in reasonable amounts. It was found that a relatively stable glass with suitable viscosity could be obtained by mixing 65 wt% TIRME F+L with 35 wt% glass cullet. The heat treatment required to crystallise the glass produced from this mixture, designated TIR65, was nucleation at 560°C for 35 min followed by crystal growth at 100°C for 120 min. The resulting glass-ceramic contained a number of crystalline phases, the most stable being clinoenstatite (MgSiO₃), or perhaps a pyroxenic phase which incorporates Ca, Mg and Al in its composition, and åkermanite (Ca₂MgSi₂O₇). The microstructure contained both fibre-like and dendritic crystals. The mechanical properties were acceptable for applications such as tiles for the building industry. ©     

Near-infrared luminescent properties of Ln:LaGdZr2O7 (Ln = Nd,Yb) transparent ceramics for solid-state laser applications

Via a facile solid reactive method, transparent Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) ceramics were successfully fabricated for the first time. The highest in-line transmittances of Nd:LaGdZr₂O₇ and Yb:LaGdZr₂O₇ ceramics reached 68% and 69%, respectively, at 1100 nm. The microstructure and crystal structure of Ln_0.1La_0.9GdZr₂O₇ transparent ceramics were fully investigated, indicating that the solid reactive technique is a good method of industrially fabricating Ln_0.1La_0.9GdZr₂O₇ transparent ceramics. The PL spectra demonstrated that Ln_0.1La_0.9GdZr₂O₇ ceramics can effectively be excited at 808 nm and 976 nm, which correlates with the widely applied output wavelengths of AlGaAs and InGaAs laser diodes. The luminescence decay curves were also studied, showing that the average fluorescence lifetimes of Nd_0.1La_0.9GdZr₂O₇ and Yb_0.1La_0.9GdZr₂O₇ transparent ceramics was 355 μs and 663 μs, respectively. Combined with its high temperature resistance and good mechanical strength, Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) transparent ceramics can have potential applications in Nd/Yb solid-state laser construction.     

Cyclic thermal shock resistance of h-BN composite ceramics with La2O3–Al2O3–SiO2 addition

The effects of La₂O₃–Al₂O₃–SiO₂ addition on the thermal conductivity, coefficient of thermal expansion (CTE), Young's modulus and cyclic thermal shock resistance of hot-pressed h-BN composite ceramics were investigated. The samples were heated to 1000 °C and then quenched to room temperature with 1–50 cycles, and the residual flexural strength was used to evaluate cyclic thermal shock resistance. h-BN composite ceramics containing 10 vol% La₂O₃–Al₂O₃ and 20 vol% SiO₂ addition exhibited the highest flexural strength, thermal conductivity and relatively low CTE, which were beneficial to the excellent thermal shock resistance. In addition, the viscous amorphous phase of ternary La₂O₃–Al₂O₃–SiO₂ system could accommodate and relax thermal stress contributing to the high thermal shock resistance. Therefore, the residual flexural strength still maintained the value of 234.3 MPa (86.9% of initial strength) after 50 cycles of thermal shock.     

Mid‐IR transparent TeO2‐TiO2‐La2O3 glass and its crystallization behavior for photonic applications

In this report, effect of enhanced rare earth (La₂O₃) concentration on substitution of TeO₂ within ternary TeO₂‐TiO₂‐La₂O₃ (TTL) glass system has been studied with respect to its thermal, structural, mechanical, optical, and crystallization properties with an aim to achieve glass and glass‐ceramics having rare‐earth‐rich crystalline phase for nonlinear optical and infrared photonic applications. DSC analysis (10°C/min) demonstrates a progressive increase in glass‐transition temperature (T_g) from 359 to 452°C with the increase in La₂O₃ content. Continuous glass network modification with transformation of [TeO₄] to [TeO₃/TeO₃₊₁] units is evidenced from Raman spectra which is corroborated with XPS studies. While mechanical properties demonstrate enhancement of cross‐linking density in the network. These glasses exhibit optical transmission window extended from 0.4 to 6 μm with calculated zero dispersion wavelength (λ_ZDW) varying from 2.41 to 2.28 μm depending upon La₂O₃ content. Crystallization kinetics of TTL10 (80TeO₂‐10TiO₂‐10La₂O₃ in mol%) glass has been studied via established models. Activation energy (E_a) has been evaluated and dimensionality of crystal growth (m) suggests formation of surface crystals. Glass‐ceramic with crystalline phase of La₂Te₆O₁₅ has been realized in heat‐treated TTL10 glass samples (at 450°C). As predicted from DSC analysis, FESEM study unveils the formation of surface crystallized glass‐ceramics.