Glass-ceramic Route Research Articles

Enhancement of sodium ion conductivity in phosphate-based glass-ceramics by chemical substitution approach

A NASICON-type sodium-ion conducting material was synthesized via the glass-ceramic route by investigating the zinc doped Na2O–Al2O3–TiO2–P2O5 system. The glasses and glass-ceramics corresponding to the formula Na2+xAl1-xZnxTi(PO4)3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1), labeled as (NAZTP-Gx) and (NAZTP-GCx) respectively, were characterized using different techniques. Differential Scanning Calorimetry (DSC) measurements were carried out to identify the characteristic temperatures, the glass transition (Tg) and the crystallization temperature (Tc). X-ray Diffraction (XRD) analysis of the glass-ceramics confirmed the formation of a solid solution Na2+xAl1-xZnxTi(PO4)3 NASICON phase, Theoretical calculations employing the Perdew–Burke–Ernzerhoff generalized gradients approximation (PBE-GGA) model supported the potential substitution of aluminum by zinc in the octahedral site in the NASICON-phase. Further structural insights were obtained through Infrared (IR) and Raman spectroscopies. Scanning electron microscopy (SEM) analysis revealed a distinct flower-like shape of the formed crystallites in the glass-ceramic NAZTP-GC0.2. Electrical characterization using electrochemical impedance spectroscopy (EIS) demonstrated that the NAZTP-GC0.2 sample exhibited the highest ionic conductivity at 300 °C, reaching 4.1 × 10−5 (Ω−1 cm−1) with an activation energy of 0.25 eV. The DC polarization was performed on the NAZTP-GC0.2 glass-ceramic, revealing that the ions are the main charge carriers in the sample. This comprehensive analysis provides valuable insights into the partial zinc doping of NASICON glass-ceramics, offering potential for improved performance as solid electrolytes in various applications.

An overview of oxidation in hybrid and glass-based protective coatings for thermoelectric materials for medium-temperature range applications

ABSTRACT Several oxidation protective coatings, both glass-based and ceramic/polymer hybrid coatings, for p- and n-type thermoelectrics were designed at the Politecnico di Torino in recent years, and they were characterised and tested under relevant conditions. The ‘glass-ceramic route’ to obtain a thermo-mechanical compatible and high-temperature resistant coated thermoelectric is discussed with some examples. Oxidation tests demonstrated the effectiveness of the coatings for the protection of both n- and p-type thermoelectrics.

Glass-ceramic route to NASICON-type Na Ti2(PO4)3 electrodes for Na-ion batteries

Glass-ceramic processes to prepare NASICON-type Na x Ti 2 (PO 4 ) 3 , which is an anode candidate for sodium-ion batteries, from 30Na 2 O–40TiO 2 –30P 2 O 5 glass have been investigated with varied atmospheric conditions. By annealing in the inert (N 2 ) atmosphere, the glass started crystalizing into NASICON-type NaTi 2 (PO 4 ) 3 with rhombohedral symmetry at ∼600 °C followed by crystallization of other phases to be multiphase mixtures at higher temperatures. In contrast, in the reducing (5% H 2 /Ar) atmosphere, NASICON-type Na 3 Ti 2 (PO 4 ) 3 with triclinic symmetry is crystallized at >∼800 °C. The formation of Na 3 Ti 2 (PO 4 ) 3 is associated with a loss of excess oxygens in the initial glass composition and a reduction of Ti from Ti 4+ to Ti 3+ . The reduction process upon the glass-to-ceramic conversion was traced by in-situ observation during the thermogravimetric analysis. It is also revealed that the electrochemical Na + -storage capabilities of the glass-ceramic electrodes are correlated with the Na-ion occupancy between these two phases, and their phase fractions affect the charge-discharge properties of Na-ion cells. Finer glass-ceramic powders could improve the electrochemical properties and achieve almost 80% of its theoretical capacity.

Effects of B2O3 on crystallization kinetics, microstructure and properties of Li1.5Al0.5Ge1.5(PO4)3-based glass-ceramics

Lithium-ionic conductors of Li1+xAlxGe2-x(PO4)3 family are considered as one of the most attractive solid electrolytes. Li1.5Al0.5Ge1.5(PO4)3 composition obtained by glass-ceramic route exhibits the highest electrical conductivity at room temperature. The introduction of sintering additives makes it possible to modify the properties of solid electrolytes. Glass-ceramics of the Li1.5Al0.5Ge1.5(PO4)3–xB2O3 series (x = 0, 0.05, 0.1, 0.15, 0.2 wt%) was obtained by glass crystallization at optimal conditions of heat treatment. The influence of B2O3 additive on thermal stability and crystallization process of initial glasses was studied by DSC method. The phase composition, microstructure and transport properties of glass-ceramics were investigated by XRD, SEM and impedance spectroscopy, respectively. The structure of the glass-ceramics was characterized by Raman spectroscopy. Glass-ceramics was found to be single-phase (R-3c) when 0 ≤ x ≤ 0.15, but impurity phases Li4P2O7 and AlPO4 appear at x = 0.20. The conductivity of B2O3-added solid electrolytes is higher compared to the pristine Li1.5Al0.5Ge1.5(PO4)3. Its ionic conductivity reached 5.5 × 10−4 S cm−1 at 25 °C. The obtained glass-ceramic electrolytes are promising for use in all-solid-state lithium-ion batteries.

Fast Ion Conduction of Sintered Glass-Ceramic Lithium Ion Conductors Investigated by Impedance Spectroscopy and Coaxial Reflection Technique

As the ionic conductivity of solid-state lithium ion conductors rises, knowledge of the detailed conductivity mechanisms is harder to obtain due to the limited frequency resolution of the traditional impedance spectrometers. Moreover, the data is easily affected by the local microstructure (i.e. pores, grain-boundaries) and the preparation conditions. The aim of this work is to demonstrate the feasibility of the coaxial reflection technique as a reliable tool to study fast ionic conductors (i.e. σ > 10−4 S cm−1). Especially the relative permittivity can be determined more accurately at room temperature. For the first time the electrical performance of LATP and LLZO manufactured via a scalable top-down glass-ceramic route is evaluated. The density turns out to be a key parameter influencing both relative permittivity and resulting conductivities. For a 100% dense LATP sample the coaxial reflection technique reveals a high grain-core conductivity of 6 × 10−3 S cm−1 similar to the conductivity of ideal single crystals.

Novel sodium superionic conductor of the Na1+yTi2SiyP3-yO12 series for application as solid electrolyte

In the search for new materials to be used as solid electrolytes, this paper discusses the substitution of phosphorus with silicon in the NaTi2(PO4)3 NASICON (Na-Super Ionic Conductor) compound, giving rise to the Na1+yTi2SiyP3-yO12 series. In fact, the substitution of P+5 for Si+4 enables the increase in the Na+ charger carrier concentration. The solid electrolytes are synthetized by the glass-ceramic route, which consists in the controlled crystallization of a precursor glass subjected to specific heat treatment. Experimental results indicate that precursor glasses are successfully crystallized in compositions containing y ≤ 1.2. X-ray diffraction patterns show the formation of NASICON phase in the Na1+yTi2SiyP3-yO12 glass-ceramics for y ≤ 0.8. However, with further addition of silicon, the major crystalline phase obtained is the Na(TiO)(PO4) phase. Surprisingly, the electrical characterization reveals that the y = 1.0 sample, whose main phase is the non-NASICON Na(TiO)(PO4), exhibits the lowest activation energy (0.31 eV) and the highest ionic conductivity of 1.0 × 10−4 S cm−1 at room temperature and 1.7 × 10−2 S cm−1 at 300 °C. Rietveld refinement and electrical conductivity results suggest that the increased ionic conductivity in the Na(TiO)(PO4) phase is due to the inclusion of some Si+4 ions in its structure, thus forming a new and highly Na(TiO)((Si)PO4) conductive phase.

Investigation on crystallization kinetics and luminescent properties of Eu2+/Eu3+-coactivated hexacelsian based glass ceramics

The thermal properties and crystallization behavior of MgOBaOSiO2B2O3Al2O3 glass have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). After crystallization at temperature (800 °C) close to the DSC crystallization peak, dendritic hexacelsian crystals are found to form as the major crystalline phase among glass. The crystallization kinetics was studied by analyzing DSC curves with Chen's and Ozawa's equations. The mean crystallization activation energy and Avrami's parameter are evaluated to be 229 kJ/mol and 1.4, indicating that the crystallization process occurs predominantly by surface crystallization as consistent with experimental data. Concurrent emissions of Eu2+ and Eu3+ under 304 nm excitation demonstrate that partial reduction of Eu3+ to Eu2+ occurs, which could be ascribed to the partition of Eu3+ into the precipitated hexacelsian crystals during the sintering process of glass ceramics. These results indicate that glass ceramic route may serve as an intriguing way for synthesis of phosphors applicable to lighting and display fields.

Fabrication and microwave dielectric properties of CuO-B 2 O 3 -Li 2 O glass-ceramic with ultra-low sintering temperature

Abstract CuO-B 2 O 3 -Li 2 O (CBL) glass-ceramic with a composition of 32 wt% CuO − 63 wt% B 2 O 3 − 5 wt% Li 2 O was prepared through conventional glass-ceramic route. The CBL glass-ceramic could be densified well by sintering at 625 °C for 30 min. The X-Ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicated that the CuB 2 O 4 phase was dominated in the sintered glass-ceramic, which showed excellent microwave dielectric properties with e r = 5.84, Q × f = 10120 GHz (at 13.44 GHz), and τ f = −33 ppm/°C. Furthermore, the CBL material is chemically compatible with both silver (Ag) and aluminum (Al) electrodes at their sintering temperatures. These properties indicate that the CBL glass-ceramic might be a promising ultra-low temperature co-fired ceramic (ULTCC) material for packaging substrate applications.

A new NASICON lithium ion-conducting glass-ceramic of the Li1 + xCrx(GeyTi1 − y)2 − x(PO4)3 system

We propose a new lithium ion-conducting glass-ceramic based on the Li1+xCrx(GeyTi1−y)2−x(PO4)3 (LCGTP) system. A specific composition (x=y=0.4) of this system was synthesized by the melt-quenching method, followed by crystallization. The crystallization behavior of the precursor glass was examined by differential scanning calorimetry(DSC) and infrared spectroscopy (IR). The main results indicate that the LCGTP precursor glass presents homogeneous nucleation and considerable glass stability, which allows solid electrolytes to be obtained by the glass-ceramic route. After heat treatment, this glass crystallizes in a NASICON LiTi2(PO4)3-type phase, demonstrating that the proposed system can accommodate Cr, Ti and Ge in an octahedral site. Different heat treatment temperatures were employed to obtain these glass-ceramics. Ionic conductivity was measured by electrochemical impedance spectroscopy (EIS). The sample heat-treated at 900°C for 12h showed the highest ionic conductivity at room temperature (6.6×10−5Ω−1cm−1). This specific glass-ceramic presented a remarkably low activation energy (0.274eV) related to grain contribution, which culminated in a grain conductivity of 8.5×10−4Ω−1cm−1 at room temperature. In addition, a correlation was found between the cell volume and the activation energy for lithium conduction. The samples' microstructures were examined by scanning electron microscopy (SEM) and were also correlated to their ionic conductivity. This set of results suggests that the proposed system is promising for the development of fast lithium ion-conducting glass-ceramics with further compositional optimization.

Stable colloidal solutions of strontium hexaferrite hard magnetic nanoparticles.

Herein we demonstrate an approach to prepare a colloidal solution of strontium hexaferrite via a glass-ceramic route. The as obtained colloids are stable and resistive to aggregation or sedimentation. They reveal outstanding magnetic and magneto-optical properties because of their platelet-like anisotropic shape and high permanent magnetic moment.

Hexaferrite submicron and nanoparticles with variable size and shape via glass-ceramic route

Strontium hexaferrite single domain particles embedded in the borate matrix were synthesized by the glass-ceramic method. The composites exhibit various morphologies depending on the initial glass composition and the thermal treatment conditions. The obtained materials contain magnetic particles with the average size ranging from tens to hundreds nanometers and with the magnetic properties changing from superparamagnetic to hard magnetic with record-high coercivities exceeding 10 kOe.

Fabrication of olivine-type LiMn xFe 1− xPO 4 crystals via the glass–ceramic route and their lithium ion battery performance

The olivine-type LiMn x Fe 1− x PO 4 crystals are fabricated through the crystallization of Li 2O–MnO 2–Fe 2O 3–P 2O 5 glasses, and the lithium ion battery performance (electrochemical charge/discharge patterns) for the glass–ceramics with LiMn x Fe 1− x PO 4 crystals is examined. It is found that homogeneous glasses are obtained for the stoichiometric compositions corresponding to LiMn x Fe 1− x PO 4 with 0 ≤ x ≤ 0.8 in a conventional melt-quenching method in air. The heat treatment of the mixtures of glass powders and glucose (5 wt%) at crystallization temperatures (∼550 °C) in a reducing atmosphere of 7%H 2–93%Ar gives the formation of the olivine-type LiMn x Fe 1− x PO 4 crystals. The charge/discharge curves exhibit the plateaus at the voltage of ∼3.4 and 4.1 V.

Cellular Anorthite Glass-Ceramics: Synthesis, Microstructure and Properties

Highly permeable cellular anorthite glass ceramics with porosity of ∼95% were obtained by a simple replication technique using near-stoichiometric glass powders and a polymeric foam as sacrificial template material. Impacts of sintering conditions and additions of minor constituents, respectively, on microstructural evolution and resulting macroscopic properties of the derived foams were investigated by X-ray diffraction, scanning electron microscopy (SEM), differential thermal analysis and X-ray microcomputer tomography. Apparent activation energies of crystallization and the Avrami coefficient were estimated from nonisothermal crystallization experiments to evaluate the impact of titania and zirconia, respectively, as potential nucleation agents. Consistent with SEM analyses, it was found that crystal growth occurs in two dimensions. While TiO2 primarily acts on the viscosity of the precursor glass and, thus, on the process of sintering by viscous flow, ZrO2 is found to exhibit at least some nucleation efficiency. As compared with sintering of ceramic powders and solid-state reactions in general, the glass ceramic route enables significant reduction in sintering time and temperature.

Crystallization behaviour of sol-gel derived cordierite precursors

Cordierite (Mg2Al4Si5O18) ceramics is technologically important material due to its low thermal expansion, small dielectric constant, and high chemical and thermal stability [1]. It occurs in two stable forms: in the high-temperature hexagonal α form, stable above 1450 °C, [2] and in the orthorhombic beta form, stable below 1450 °C [3]. Preparation roots of cordierite involve solid-state reactions, liquid phase sintering, glass-ceramic route or sol-gel synthesis. The interest in sol-gel synthesis lately increased because it enables excellent control of chemical composition and reduces the temperature of ceramic processing. Two sol-gel derived cordierite precursors were prepared using tetraetoxysilane, Mg(NO3)2• 6H2O and Al-sec-butoxide (for precursor designated as BC) or Al(NO3)3• 9H2O (for precursor designated as NC). Detailed studies of crystallization behaviour of those precursors were performed by DSC and in-situ high temperature XRD from RT up to 1165 °C. The Rietveld method was performed for quantitative phase analysis of the crystallization products and for the refinement of their crystal structures. Crystallization started at ~800 °C for both precursors, but their crystallization sequences were rather different. For precursor BC crystallization involved the appearance of stuffed derivative of beta-quartz, α -cordierite, mullite and enstatite, while for precursor NC it involved the formation of stuffed derivative of beta-quartz, sapphirine, mullite, α -cordierite and beta-cristobalite.

Critical aspects on preparation of Bi-2223 glassy precursor by melt-process

It is well known that many Bi–Sr–Ca–Cu–O compositions are glass forming and are converted into high-critical temperature superconductors after proper annealing. Glassy precursors have been prepared by rapid quenching of nominal Bi 2Sr 2Ca 2Cu 3O 10 melts from above 1000 °C in air using different conditions. In order to fabricate superconductors having high-critical temperature and current density using the glass–ceramic route, it is necessary to clarify the total chemical composition of the quenched glasses. For the first time the total chemical composition of such melts has been directly investigated by element analysis. The oxygen content has been directly measured by carrier gas hot extraction of as-quenched melts. The investigated cation content in as-quenched nominal Bi 2Sr 2Ca 2Cu 3O 10 melts presents significant deviations in composition for the glassy precursor, foremost for the calcium content. The main reasons of the non-complete transition from nominal to obtained composition after the quenching step was showed to be due to inhomogeneous and incomplete melting. This dependency is showed to be highly affected by the nominal composition of the melt. From literature there are barely any published values of the chemical composition of the quenched glassy precursors that would however be critical to control the crystallization behavior and to understand the influences on the superconductive properties.

Glass–ceramic route of BSCCO superconductors – Fabrication of amorphous precursor

It is well known that many Bi–Sr–Ca–Cu–O compositions are glass-forming and some Bi-based glasses such as Bi 2Sr 2CaCu 2O x and Bi 2Sr 2Ca 2Cu 3O x are converted into high critical temperature superconductors after proper annealing. In order to fabricate superconductors having high- T c and high critical current density using the glass–ceramic route, it is necessary to clarify the total chemical composition of the quenched glasses prepared in most cases by rapid quenching of melts from around 1200 °C in air. The total oxygen content measured directly reflects a significant oxygen deficit due to the melting process. We have also investigated the cation content in quenched Bi 2Sr 2Ca 2Cu 3O x precursors and found that there are substantial differences from the nominal composition to the quenched materials especially for calcium. Such glasses also show some CaO crystalline reflexes in the XRD patterns.

Nanocrystalline nickel-zinc ferrite prepared by the glass-ceramic route

Ni 0.5Zn 0.5Fe 2O 4 crystals having dimensions in the range 15–29 nm have been grown within borate glass by a two-stage heat treatment in the temperature range 873–953 K. Magnetic measurements have been carried out over the temperature range 20–300 K. The maximum coercive force corresponding to 0 K, ( H co) ∼ 334 Oe, is obtained for a sample containing ferrite crystals of median diameter 15 nm. Field-cooled and zero-field-cooled magnetization data for different samples are consistent with the blocking temperatures extracted from the variation of coercive force as a function of temperature. The magnetocrystalline anisotropy constant for nanocrystalline nickel-zinc ferrite is found to be an order of magnitude higher than that for the bulk material.

A new model for the formation of high-T c phase in superconductive (Bi, Pb)2Sr2Ca2Cu3O x glass-ceramics

The formation mechanism of the high-T c phase through the glass-ceramic route and the role of Pb on the formation of this phase have been investigated. It was found that a new compound with the chemical composition Pb2Sr3 − x Ca x CuO y (x = 1.8) precipitates at around 550‡C. This phase is stable up to 800‡C, where it begins to decompose, and at 850 ‡C it completely disappears. It was found that some part of the released Pb diffuses into the 2212 phase leading to the formation of Pb-containing 2212 phase, (Bi, Pb)2Sr2CaCu2O x . On the other hand, an endothermic peak, probably arising from the melting of (Bi, Pb)2Sr2CaCu2O x phase or melting at grain boundaries containing Pb2+, was observed at 856‡C only in Pb-containing samples that were heat treated. The liquid phase attributed to the endothermic peak may enhance the formation of high-T c phase (2223 phase). The growth kinetics for the high-T c phase were analysed using the Johnson-Mehl-Avrami equation; the results indicate that the growth of the high-T c phase is controlled by a diffusion process and the activation energy for its formation in the initial stage (shorter than 96 h) is 576 ± 45 kJ mol−1.

Optical reflectivity of superconducting Bi 3.9Pb 0.1Sr 3Ca 3Cu 4O x obtained by glass-ceramic route in 0.6–6.2 eV range

The room temperature reflectance spectra in the UV-VIS-NIR region (0.6–6.2 eV) for the superconducting ceramic phase of Bi 3.9Pb 0.1Sr 3Ca 3Cu 4O x, obtained by glass-ceramic route have been studied by Kramers-Kronig (KK) analysis. From these analyses, the real (ε′) and imaginary (ε″) parts of the complex dielectric function, ε = ε′ + iε″, optical conductivity (σ′) and the absorption spectra (α) have been determined. These studies have indicated the presence of plasmon around 1 eV and have also shown that in these oxide systems, BiO and SrO layers have little role to play in the mechanism of superconductivity. The possibility of excitonic absorption in Bi-based high T c superconductors has also been discussed from the knowledge of the absorption spectra.

Fabrication, microstructure, and mechanical properties of TaC particulate and SiC fiber-reinforced lithia-alumina-silica composites

Additions of O to 9 mol % Ta2O5 to a lithia-alumina-silica glass-ceramic matrix Nicalon SiC-reinforced composite increased the elastic modulus and ultimate strength of the composite. The additive fostered sphereulitic growth of β-eucriptite solid solution crystals which concentrated Ta2O5 at sphereulite boundaries and adjacent to the fiber-matrix carbon-rich interphases. These regions reacted with the interphases as well as soluble carbon monoxide gas to convert them to TaC. The former reaction was shown to be thermodynamically favorable above 983 °C, while the latter was favorable above 1249 °C. The improvement in mechanical properties was attributed to TaC particulate reinforcement, and suggests a simple glass-ceramic route to the fabrication of particulate-reinforced ceramic matrix composites.