Bismuth sesquioxide attracts considerable attention due to the numerous stable and metastable phases it exhibits in nature, as well as the diverse range of properties it displays. Despite their high potential for numerous applications, surprisingly few investigations have been carried out on nanocomposites where the stability range of particular crystallographic phases has been significantly extended in the form of nanocrystallites embedded in a residual amorphous matrix. Quite recently, nanocrystallites of delta-like Bi2O3 phase were observed at room temperature, confined in Bi2O3-Al2O3-SiO2 glassy matrix. In this work, we performed 27Al and 29Si solid-state NMR, HT-XRD, and TEM with EDS/EELS microanalysis experiments to clarify the role of Al and Si additives, which had been barely understood. These systematic investigations provided evidence that neither Al nor Si additives are incorporated into the delta-like Bi2O3 phase. Instead, their local environments remain similar to those in pristine glass. Therefore, we postulate that it is the size and strain effects that provide the delta-like phase stabilisation in the nanocomposite glass-ceramics studied in this work, making it a fascinating phenomenon for further studies.

The report presents the electrical, structural, and microstructural properties of high-pressure–high-temperature-treated (HPHT) composites composed of δ-like Bi2O3 nanograins embedded in an aluminosilicate glassy matrix. Nanocomposites were obtained by heat treatment of the Bi2O3-Al2O3-SiO2 ternary glass system, followed by high-pressure molding (above 750 MPa). The total oxygen conductivity σt of the studied nanocomposites was high and approached a value of 4.5 × 10−4 S/cm at 600 °C. Due to HPHT treatment, we could also determine the intragrain conductivity of δ-Bi2O3 nanocrystallites. In this case, the value of σδ was even higher and was equal to 1.3 × 10−3 S/cm at 600 °C. It was also possible to study the temperature dependence of intragrain conductivity, showing two activation energies, which probably reflect the order–disorder transition within the sublattice of mobile O2− ions. The obtained nanocomposites exhibited promising properties for applications in electrochemical devices operating in the intermediate temperature range from 300 to 600 °C.

Olivine-like NaFePO4 glasses and nanocomposites are promising materials for cathodes in sodium batteries. Our previous studies focused on the preparation of NaFePO4 glass, transforming it into a nanocomposite using high-pressure–high-temperature treatment, and comparing both materials’ structural, thermal, and DC electric conductivity. This work focuses on specific features of AC electric conductivity, containing messages on the dynamics of translational processes. Conductivity spectra measured at various temperatures are scaled by apparent DC conductivity and plotted against frequency scaled by DC conductivity and temperature in a so-called master curve representation. Both glass and nanocomposite conductivity spectra are used to test the (effective) exponent using Jonscher’s scaling law. In both materials, the values of exponent range from 0.3 to 0.9, with different relation to temperature. It corresponds to the electronic conduction mechanism change from low-temperature Mott’s variable range hopping (between Fe2+/Fe3+ centers) to phonon-assisted hopping, which was suggested by previous DC measurements. Following the pressure treatment, AC conductivity activation energies were reduced from EAC≈0.40 eV for glass to EAC≈0.18 eV for nanocomposite and are lower than their DC counterpart, following a typical empirical relation with the value of the exponent. While pressure treatment leads to a 2–3-orders-of-magnitude rise in the AC and apparent DC conductivity due to the reduced distance between the hopping centers, a nonmonotonic relation of AC power exponent and temperature is observed. It occurs due to the disturbance of polaron interactions with Na+ mobile ions.

This report presents the pressure-temperature (p-T) plane of Bi2O3-Al2O3-SiO2 ternary system in the context of nanocrystallite formation from its amorphous state. The diagram was constructed through differential thermal analysis (DTA) performed in situ under high-pressure-high-temperature (HP-HT) conditions, with nitrogen serving as the pressurizing medium. Above the glass transition temperature Tg, a wide ultraviscous, supercooled liquid state spanning approximately 150 K is observed. Later heating transforms this state into nanocrystallites embedded within an amorphous matrix, thereby keeping distinctive structural characteristics even after the decompression process. The p-T plane serves as a fundamental prerequisite for the design of nanocrystallites within a glass matrix, a well-established technique known as glass-ceramics. Various paths within the p-T plane, followed by annealing just below Tg, can be explored, potentially leading to the development of Bi2O3-based materials with enhanced electrical, dielectric, photonic, and mechanical properties, predicated on nanocrystallites formed by high-pressure treatment.

Several bismuth sesquioxide (Bi _2 O _3 ) phases (namely , and -like) were previously stabilized at room temperature by nanocrystallization of bismuthate glasses. Normally, a monoclinic phase is the stable one at ambient conditions in polycrystalline materials. In this work, we wanted to observe if any phase transitions would occur below the room temperature for , and -like phases confined in a residual glassy matrix. Observations were made down to 100 K using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Both experimental techniques showed no traces of phase transition upon cooling to the temperature limit of our equipment. From XRD studies, the lattice parameter of the δ-like phase was determined. The values were compared to the values calculated by molecular dynamics studies of overcooled -Bi _2 O _3 phase.

Recently, an interest in NASICON-type materials revived, as they are considered potential cathode materials in sodium–ion batteries used in large-scale energy storage. We applied a facile technique of thermal nanocrystallization of glassy analogs of these compounds to enhance their electrical parameters. Six nanomaterials of the Na3M2(PO4)2F3 (M = V, Ti, Fe) system were studied. Samples with nominal compositions of Na3V2(PO4)2F3, Na3Ti2(PO4)2F3, Na3Fe2(PO4)2F3, Na3TiV(PO4)2F3, Na3FeV(PO4)2F3 and Na3FeTi(PO4)2F3 have been synthesized as glasses using the melt-quenching method. X-ray diffraction measurements were conducted for as-synthesized samples and after heating at elevated temperatures to investigate the structure. Extensive impedance measurements allowed us to optimize the nanocrystallization process to enhance the electrical conductivity of cathode nanomaterials. Such a procedure resulted in samples with the conductivity at room temperature ranging from 1×10−9 up to 8×10−5 S/cm. We carried out in situ impedance spectroscopy measurements (in an ultra-high-frequency range up to 10 GHz) and compared them with thermal events observed in differential thermal analysis studies.

This paper presents results for systems formed in a solid glassy state after nanocrystallization process above the glass temperature. We analyze electric conductivity and relaxation processes after such treatment under high temperature (HT) and high pressure (HP-HT) as well. The latter leads to ca. 8% increase of density, two decades (100) increase of electric conductivity as well as qualitative changes in relaxation processes. The previtreous-type changes of the relaxation time on cooling is analyzed by the use of critical-like and the 'critical-activated' description. Presented results correspond well with obtained for this material and shown in ref. [8]. The evidence for pressure evolution of the glass and crystallization temperatures, indicating the unique possibility of maxima and crossovers is also reported.

A new nanocomposite material was prepared by high pressure processing of starting glass of nominal composition NaFePO4. Thermal, structural, electrical and dielectric properties of the prepared samples were studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and broadband dielectric spectroscopy (BDS). It was demonstrated that high-pressure-high-temperature treatment (HPHT) led to an increase in the electrical conductivity of the initial glasses by two orders of magnitude. It was also shown that the observed effect was stronger than for the lithium analogue of this material studied by us earlier. The observed enhancement of conductivity was explained by Mott's theory of electron hopping, which is more frequent in samples after pressure treatment. The final composite consisted of nanocrystalline NASICON (sodium (Na) Super Ionic CONductor) and alluaudite phases, which are electrochemically active in potential cathode materials for Na batteries. Average dimensions of crystallites estimated from XRD studies were between 40 and 90 nm, depending on the phase. Some new aspects of local dielectric relaxations in studied materials were also discussed. It was shown that a combination of high pressures and BDS method is a powerful method to study relaxation processes and molecular movements in solids. It was also pointed out that high-pressure cathode materials may exhibit higher volumetric capacities compared with commercially used cathodes with carbon additions.

LiFePO4 is an important base material for generation of new batteries. One of the important developments is its use in the form of a solid glass, which allows an increase in the electrical conductivity after the high-pressure process. Such a treatment allows full control of the vitrification and nanocrystallization processes as well. This report shows the basic reference for the pressure dependence of the glass transition temperature. The unique behavior has been proven with a maximum of Tg (P) already at moderate pressures. The protocol for depicting the resulting evolution is as follows: it enables a reliable extrapolation beyond the experimental domain. The importance of the presented results for the general topic of glass transition physics is also remarkable due to the scant evidence of the existence of systems with clearly inverted vitrification under compression.

This study demonstrated for the first time that it is possible to prepare nanocrystalline δ-Bi2O3 that is stable at room temperature by twin-rollers and free cooling methods, using a ceramic crucible. The phase composition of prepared samples and upper limit of the thermal stability of nanograins confined in an amorphous matrix were determined by the X-ray diffraction (XRD) method. The average size of crystallites and the microstructure of studied samples was determined by SEM and XRD methods. The average grain size varied from 38 to 85 nm, depending on the preparation technique; however, it was also observed that agglomerations consisted of smaller crystallites ca. 10–30 nm. Using the EDX method, it was found that a crucial role in the preparation of nanocrystalline δ-Bi2O3 glass-ceramics was played by Si and Al impurities and their glass forming oxides from ceramic crucible. By impedance spectroscopy (IS), the temperature dependencies of electric conductivity (via oxygen ions) were studied and the activation energies of conductivity were determined.

This review article presents recent studies on nanostructured glass-ceramic materials with substantially improved electrical (ionic or electronic) conductivity or with an extended temperature stability range of highly conducting high-temperature crystalline phases. Such materials were synthesized by the thermal nanocrystallization of selected electrically conducting oxide glasses. Various nanostructured systems have been described, including glass-ceramics based on ion conductive glasses (silver iodate and bismuth oxide ones) and electronic conductive glasses (vanadate-phosphate and olivine-like ones). Most systems under consideration have been studied with the practical aim of using them as electrode or solid electrolyte materials for rechargeable Li-ion, Na-ion, all-solid batteries, or solid oxide fuel cells. It has been shown that the conductivity enhancement of glass-ceramics is closely correlated with their dual microstructure, consisting of nanocrystallites (5–100 nm) confined in the glassy matrix. The disordered interfacial regions in those materials form “easy conduction” paths. It has also been shown that the glassy matrices may be a suitable environment for phases, which in bulk form are stable at high temperatures, and may exist when confined in nanograins embedded in the glassy matrix even at room temperature. Many complementary experimental techniques probing the electrical conductivity, long- and short-range structure, microstructure at the nanometer scale, or thermal transitions have been used to characterize the glass-ceramic systems under consideration. Their results have helped to explain the correlations between the microstructure and the properties of these systems.

In our recent papers, it was shown that the thermal nanocrystallization of glassy analogs of selected cathode materials led to a substantial increase in electrical conductivity. The advantage of this technique is the lack of carbon additive during synthesis. In this paper, the electrochemical performance of nanocrystalline LiFePO4 (LFP) and LiFe0.88V0.08PO4 (LFVP) cathode materials was studied and compared with commercially purchased high-performance LiFePO4 (C-LFP). The structure of the nanocrystalline materials was confirmed using X-ray diffractometry. The laboratory cells were tested at a wide variety of loads ranging from 0.1 to 3 C-rate. Their performance is discussed with reference to their microstructure and electrical conductivity. LFP exhibited a modest electrochemical performance, while the gravimetric capacity of LFVP reached ca. 100 mAh/g. This value is lower than the theoretical capacity, probably due to the residual glassy matrix in which the nanocrystallites are embedded, and thus does not play a significant role in the electrochemistry of the material. The relative capacity fade at high loads was, however, comparable to that of the commercially purchased high-performance LFP. Further optimization of the crystallites-to-matrix ratio could possibly result in further improvement of the electrochemical performance of nanocrystallized LFVP glasses.

Bismuth sesquioxide ([Formula: see text]) draws much attention due to wide variety of phases in which it exists depending on the temperature. Among them, [Formula: see text] phase is specially interesting because of its high oxide ion conductivity and prospects of applications as an electrolyte in fuel cells. Unfortunately, it is stable only in a narrow temperature range ca. 730-830 [Formula: see text]C. Our group has developed a facile and reproducible two-stage method of stabilizing [Formula: see text] crystalline phases confined in nanocrystallites embedded in amorphous matrix. In the first stage, glassy materials were obtained by a routine melt-quenching method: pure [Formula: see text] powders were melted in porcelain crucibles and fast-cooled down to room temperature. In the second step, the materials were appropriately heat-treated to induce formation of crystallites of [Formula: see text], [Formula: see text] or [Formula: see text] [Formula: see text] phases confined in a glassy matrix, depending on the process conditions. It was found out that the vitrification of the initial [Formula: see text] and the subsequent nanocrystallization were unexpectedly possible due to the presence of some Al, and Si impurities from the crucibles. Systematic DTA, XRD, optical, Raman and SEM/EDS studies were carried out to investigate the influence of the syntheses processes and allowed us to determine conditions under which the particular phases appear and remain stable down to room temperature.

The oxide-based Li+ conductors are considered as potential solid electrolytes for lithium-ion batteries. Among the NASICON–type materials, Li1.3Al0.3Ti1.7(PO4)3 (LATP) seems to be a promising candidate for application. Although its bulk conductivity is of the order of 10−3 S · cm−1, and seems to be sufficient for practical use, the total conductivity is considerably limited by the highly resistant grain boundaries. This shortcoming may be overcome by the formation of LATP–based ceramics with appropriate sintering aids. In this study, the 0.75Li2O·0.25B2O3 (LBO) glass with low melting point was chosen to improve the ionic conductivity of LATP. The properties of Li1.3Al0.3Ti1.7(PO4)3–y (0.75Li2O·0.25B2O3) (0 ≤ y ≤ 0.3) system were studied by means of: high temperature X-ray diffractometry (HTXRD), 6Li/7Li, 11B, 27Al and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density methods. Based on the experimental results, it is shown that the use of LBO glass as a sintering aid results in the enhancement of the total ionic conductivity of LATP ceramics. The correlations between apparent density, microstructure, composition, sintering temperature and ionic conductivity are presented and discussed. The presumed mechanism of the conductivity enhancement is analyzed in terms of the brick-layer model (BLM). The highest value of the total ionic conductivity, equal to 1.9 × 10−4 S · cm−1, was obtained for LATP–0.1LBO sintered at 800 °C.

Six NASICON-type phosphate glasses with a wide variety of compositions (Na3M2(PO4)(2)F-3, where M-2 = V-2, Ti-2, Fe-2, TiV, FeV, and FeTi) were synthesized using melt-quenching and double-crucible techniques. Their glass transition and crystallization temperatures were determined from differential thermal analysis experiments. The electrical properties were studied with impedance spectroscopy. We found that depending on temperature and composition the studied materials exhibit predominant electronic, ionic, or mixed conduction. This observation is interesting from both fundamental and application point of view (eg, in all-solid-state batteries). In general, the conductivity of glasses ranged from 3 center dot 10(-13) to 10(-10) S/cm at room temperature, with activation energies varying from 0.65 to 0.73 eV. After crystallization at 600 degrees C, the values of conductivity noticeably increased. For nanocrystalline materials, they were between 10(-11) and 10(-7) S/cm (at room temperature). The values of the activation energy spread from 0.53 to 0.70 eV. Most of the glasses exhibited predominant electronic conductivity. After nanocrystallization, the ionic transference number considerably increased in almost all samples. This study proves that thermal nanocrystallization can be used to synthesize nanocrystalline NASICON-like cathode materials for Na-ion batteries from their glassy analogs. We believe that this method can be adopted also to other interesting sodium compounds in the future.

A glassy sample with a nominal formula LiMn 1 − 3 x /2 V x BO 3 (where x = 0.05) was synthesised using the melt-quenching method. Material was characterised by differential thermal analysis (DTA), X-ray diffactometry (XRD) at room temperature and as a function of temperature (HT-XRD), X-ray photoelectron spectroscopy (XPS), impedance spectroscopy (IS) and scanning electron microscopy (SEM). Dependences of glass transition and crystallisation temperatures on the heating rate in DTA experiments were determined. The initial value of electrical conductivity of the glass was 1.4 × 10 − 15 Scm − 1 . It was significantly increased by a proper thermal nanocrystallisation. The maximum value was higher by 6 orders of magnitude and reached 2.6 × 10 − 9 Scm − 1 at room temperature. Expected crystalline phases (i.e. monoclinic and hexagonal LiMnBO 3 ) upon heating were identified and assigned to thermal events observed with DTA. Microstructure of nanocrystalline samples observed by SEM revealed nanocrystalline grains noticeably smaller than 100 nm. Results explaining nanocrystallisation process are coherent.

We investigated the impact of high pressure and high-temperature annealing on lithium-vanadium-iron-phosphate (LiFe0.75V0.10PO4) glass materials, proposed for the use in cathodes for high-performance batteries. The treatment was carried out below the glass transition temperature (Tg ≈ 483 °C) at P = 1 GPa pressure, in an argon atmosphere. It led to the multifold electrical conductivity increase. Broadband dielectric spectroscopy (BDS) measurements before and after the process revealed the strong DC-conductivity increase across the whole studied frequency range by two orders of magnitude. The phenomenon is explained using Mott’s theory of polaron hopping in disordered solids containing transition metal oxides. The pressure evolution of the glass transition temperature and the crystallisation temperature above Tg is shown.

Polycrystalline LiMnBO3 is a promising cathode material for Li-ion batteries. In this work, we investigated the thermal, structural and electrical properties of glassy and nanocrystallized materials having the same chemical composition. The original glass was obtained via a standard melt-quenching method. SEM and Li-7 solid-state NMR indicate that it contains a mixture of two distinct glassy phases. The results suggest that the electrical conductivity of the glass is dominated by the ionic one. The dc conductivity of initial glass was estimated to be in the order of 10(-18) S.cm(-1) at room temperature. The thermal nanocrystallization of the glass produces a nanostructured glass-ceramics containing MnBO3 and LiMnBO3 phases. The electric conductivity of this glass ceramics is increased by 6 orders of magnitude, compared to the starting material at room temperature. Compared to other manganese and borate containing glasses reported in the literature, the conductivity of the nanostructured glass ceramics is higher than that of the previously reported glassy materials. Such improved conductivity stems from the facilitated electronic transport along the grain boundaries.

In this work, a series of photoluminescent materials have been synthesized based on optically transparent and chemically stable glasses of the nominal composition Na3Al2(PO4)(2)F-3 (NaF-Al2O3-P2O5 system) doped with 1 wt % of europium. It has been shown that the synthesis conditions (mainly the temperature and duration of the melting stage under reducing conditions) strongly affected the photoluminescence spectra of the material. This effect has been ascribed to varying proportions between Eu3+ and Eu2+ ions concentrations, imposed by the synthesis conditions, which was confirmed by XPS, absorption and decay times measurements. As both Eu3+ and Eu2+ centers exhibit photoluminescence in different ranges of the visible spectra (Eu3+ -red, and Eu2+ -mainly blue) the possibility, shown by us, to control relative proportions of the oxidation states of europium and consequently to control the photoluminescence spectra, may be advantageous from the viewpoint of potential applications of such materials as novel phosphors for white LEDs with the emission spectra resembling natural light.

In this research, special attention has been paid to an observation of a metal-insulator transition (MIT) in lithium/sodium/magnesium-vanadate-phosphate glasses and nanomaterials. Two series (A & B) of glassy 90MV(2)O(5)center dot 10P(2)O(5) (M = Li, Na, Mg) samples were prepared by melt-quenching technique at 1300 degrees C using double-crucible technique. Series B was synthesized in more reducing conditions. DSC traces of the synthesized samples were typical for glassy materials. Glass transition and crystallization occurred in series A at significantly higher temperatures than in series B. In addition, an endothermic peak was observed at low temperature (67 degrees C). XRD patterns of the samples contained amorphous halo, but also some diffraction reflexes corresponding to monoclinic VO2. In series A, the reflexes had low intensity, whereas in series B the intensity of the peaks at the same positions was significantly higher. Dependences of electrical conductivity were typical for nanocrystallized glasses in case of series A, whereas in series B a reversible change of the conductivity was observed at 67 degrees C. Samples of series A exhibited positive and constant Seebeck coefficient S within wide temperature range, whereas in series B a change in thermoelectric power was observed above 67 degrees C. All these phenomena around 67 degrees C are due to metal-insulator transition in VO2 impurities in the samples.