Na-V-P-Nb-based materials have gained substantial recognition as cathode materials in high-rate sodium-ion batteries due to their unique properties and compositions, comprising both alkali and transition metal ions, which allow them to exhibit a mixed ionic-polaronic conduction mechanism. In this study, the impact of introducing two transition metal oxides, V2O5 and Nb2O5, on the thermal, (micro)structural, and electrical properties of the 35Na2O-25V2O5-(40 - x)P2O5 - xNb2O5 system is examined. The starting glass shows the highest values of DC conductivity, σDC, reaching 1.45 × 10-8 Ω-1 cm-1 at 303 K, along with a glass transition temperature, Tg, of 371 °C. The incorporation of Nb2O5 influences both σDC and Tg, resulting in non-linear trends, with the lowest values observed for the glass with x = 20 mol%. Electron paramagnetic resonance measurements and vibrational spectroscopy results suggest that the observed non-monotonic trend in σDC arises from a diminishing contribution of polaronic conductivity due to the decrease in the relative number of V4+ ions and the introduction of Nb2O5, which disrupts the predominantly mixed vanadate-phosphate network within the starting glasses, consequently impeding polaronic transport. The mechanism of electrical transport is investigated using the model-free Summerfield scaling procedure, revealing the presence of mixed ionic-polaronic conductivity in glasses where x < 10 mol%, whereas for x ≥ 10 mol%, the ionic conductivity mechanism becomes prominent. To assess the impact of the V2O5 content on the electrical transport mechanism, a comparative analysis of two analogue series with varying V2O5 content (10 and 25 mol%) is conducted to evaluate the extent of its polaronic contribution.
Niobium , Phosphates , Phosphates/chemistry , Glass/chemistry , Ions , Electron Spin Resonance Spectroscopy , Sodium/chemistry , Ceramics/chemistry
Nowadays, yttria (Y3+)-stabilized ZrO2 (Y-TZP) is the most commonly used material in dental prosthetics. Y-TZP dental ceramics are mainly stabilized via the addition of 3 mol% yttrium oxide (Y2O3). These ceramics exhibit excellent mechanical properties, including high flexural strength, fracture toughness, elastic modulus, etc. Some manufacturers have recently introduced a new class of dental materials with multilayer composition with the aim of combining the advantages of adding more or less Y2O3 to the ceramic composition in one Y-TZP material. The flexural strength values of multilayer Y-TZP may vary depending on the dimensions of the specimen, layer distributions, and especially the layer exposed on the maximum tension side, i.e., loading configuration. Although previous studies have examined the flexural strength of separate Y-TZP layers, capturing the flexural strength of multilayer Y-TZP is still challenging. However, one should keep in mind that multilayer flexural strength is important for clinical indications. The objective of this study is to compare the flexural strength of three distinct multilayer translucent Y-TZP materials made up of layers with different Y3+ contents. Rectangular samples (2 mm × 2 mm × 16 mm) were prepared from CAD/CAM discs using the milling machine Programill PM7 (Ivoclar Vivadent AG). Milled bars were tested for flexural strength in a three-point bending test (ISO 6872:2015) using a universal testing machine (Inspekt Duo 5kN; Hegewald & Peschke, Nossen, Germany) at a crosshead speed of 0.5 mm/min. Representative samples of each type of material were selected for quantitative and qualitative analysis of the microstructure. Representative samples of each type of material were selected for structural, mechanical, and microstructural analyses.
Sodium-phosphate-based glass-ceramics (GCs) are promising materials for a wide range of applications, including solid-state sodium-ion batteries, microelectronic packaging substrates, and humidity sensors. This study investigated the impact of 24 h heat-treatments (HT) at varying temperatures on Na-Ge-P glass, with a focus on (micro)structural, electrical, and dielectric properties of prepared GCs. Various techniques such as powder X-ray diffraction (PXRD), infrared spectroscopy-attenuated total reflection (IR-ATR), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were employed. With the elevation of HT temperature, crystallinity progressively rose; at 450 °C, the microstructure retained amorphous traits featuring nanometric grains, whereas at 550 °C, HT resulted in fully crystallized structures characterized by square-shaped micron-scale grains of NaPO3. The insight into the evaluation of electrical and dielectric properties was provided by Solid-State Impedance Spectroscopy (SS-IS), revealing a strong correlation with the conditions of controlled crystallization and observed (micro)structure. Compared to the initial glass, which showed DC conductivity (σDC) on the order of magnitude 10-7 Ω-1 cm-1 at 393 K, the obtained GCs exhibited a lower σDC ranging from 10-8 to 10-10 Ω-1 cm-1. With the rise in HT temperature, σDC further decreased due to the crystallization of the NaPO3 phase, depleting the glass matrix of mobile Na+ ions. The prepared GCs showed improved dielectric parameters in comparison to the initial glass, with a noticeable increase in dielectric constant values (~20) followed by a decline in dielectric loss (~10-3) values as the HT temperatures rise. Particularly, the GC obtained at @450 stood out as the optimal sample, showcasing an elevated dielectric constant and low dielectric loss value, along with moderate ionic conductivity. This research uncovers the intricate relationship between heat-treatment conditions and material properties, emphasizing that controlled crystallization allows for precise modifications to microstructure and phase composition within the remaining glassy phase, ultimately facilitating the fine-tuning of material properties.
Bismuth ferrite (BFO, BiFeO3), exhibiting both ferromagnetic and ferroelectric properties at room temperature, is one of the most researched multiferroic materials with a growing number of technological applications. In the present study, using a combined theoretical-experimental approach, we have investigated the influence of Ho-doping on the structural, electronic and magnetic properties of BFO. Synthesis and structural XRD characterization of Bi1-xHoxFeO3 (x = 0.02, 0.05, and 0.10) nanopowders have been completed. After structure prediction of Ho-doped BiFeO3 using bond valence calculations (BVC), six most favorable candidates were found: α-, ß-, γ-, R-, T1, and T2. Furthermore, all structure candidates have been examined for different magnetic ordering using DFT calculations. The magnetic behavior of the synthesized materials was investigated using a SQUID magnetometer equipped with an oven. The plethora of magnetic and electronic properties of the Ho-doped BFO that our theoretical research predicted can open up rich possibilities for further investigation and eventual applications.
Polymer hydrogels crosslinked by therapeutic metal ions have attracted increased interest in recent years due to their unique and versatile properties. Chitosan hydrogels are widely investigated for various biomedical applications such as tissue engineering and drug delivery. Copper and zinc ions are considered as therapeutic metal ions, that have important roles in bone regeneration. The aim of this study was to investigate the physicochemical and biological properties of bimetallic-chitosan complex hydrogels with different cupric and zinc ions content. Scanning electron microscopy (SEM) revealed changes in the morphology from the microstructure with larger, tubular pores for aerogels with higher Zn content, to the sheets-like structure with long pores for samples with higher Cu content. FTIR analysis indicated the formation of bimetallic-chitosan aerogels. The obtained X-ray diffraction patterns showed a broadening of chitosan's characteristic diffraction maximum, while characterization of physical properties showed decreased swelling ability and increased shear modulus with higher Cu content. ICP-MS results showed a negligible amount of copper and zinc ions released under physiological conditions during 24 h indicating a strong physical crosslink between metal ions and chitosan chains. Furthermore, accelerated in vitro degradation showed that hydrogels maintained good stability during four weeks of lysozyme activity. The MTT assay indicated that the cytotoxicity of Cu2+-Zn2+/chitosan complexes could be adjusted by the amount of cupric ions. All results imply that Cu2+ and Zn2+ ions act as physical crosslinkers of the polymer network. Also, results are in agreement with the prediction of density functional theory (DFT) which indicated stronger chitosan-Cu tetrahedral aqua complex interactions in comparison to the chitosan-[Zn(H2O)4]2+ interactions.
The aim of this study is to investigate the influence of different glass fibers made of commercial silicate, borosilicate, and laboratory-made iron-phosphate compositions, on the preparation of polylactic acid (PLA) composites and their structural and physical properties. The thermal, structural, and electrical properties of prepared PLA-glass fiber composites were studied using differential scanning calorimetry, X-ray diffraction, microscopy, and impedance spectroscopy. The structural as well as morphological, thermal, and electrical properties of all PLA-glass composites were found to be very similar and independent of the composition and aspect ratio of glass fibers. All types of glass fibers improve mechanical properties, increase thermal stability, and decrease the electrical conductivity of PLA, thereby producing mechanical strong electrically insulating composite material with potential in various applications.
Zirconia (ZrO2), a widely known material with an extensive range of applications, is especially suitable for dental applications. This kind of dental material is produced in the form of blocks or discs (mostly discs-depending on CAD/CAM machines) by cold isostatic pressing (CIP). Such discs are subsequently milled by CAM/CAD technology into a desirable form. Due to the application of CIP, the resulting discs consist of different yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) powders, additives and pigments. The diverse composition of the discs (e.g., different Y3+ content) governs material properties, such as hardness, toughness and translucence. The aim of this work was to investigate the impact of Y3+ addition on the grains and grain boundaries, on the ZrO2 phases lattice parameter values and on the electrical equivalent circuit parameters of the prepared Y-TZP samples. The disc-shaped samples were prepared by using CAM/CAD technology. It was observed that the grain size and the grain density were increased by Y3+ addition. The sample with the lowest Y3+ content was characterized by the highest portion of the tetragonal phase, whilst the disc with the highest Y3+ addition consisted mainly of the cubic phase. It was also observed that at the higher Y3+ ion concentrations, these ions mainly incorporated the tetragonal phase. Furthermore, conductivity investigations showed that the resistivity of the grains in the samples with the higher Y3+ concentrations was decreased as these ions were mainly trapped in the grain boundary. On the other hand, the Y3+ trapping increased the capacitance of the grain boundary.
A series of glass-ceramics were prepared by heat-treatments of 40Na2O-30MoO3-30P2O5 (in mol%) glass in a temperature range from 380 (Tg) to 490 °C (Tc) and for 1-24 h. The prepared glass-ceramics contain from 2 to 25 wt.% of crystalline NaMoO2PO4. The sodium-ion conductivity in these materials decreases up to one order of magnitude with an increase in the degree of crystallization due to the immobilization of sodium ions in crystalline NaMoO2PO4. The transport of sodium ions in these materials occurs primarily through the dominant continuous glassy phase, and it is weakly affected by the sporadically distributed crystalline grains. However, the prepared glass-ceramics exhibit high proton conductivity in a humid atmosphere and remarkable humidity-sensing properties; this could be related to crystalline NaMoO2PO4, which provides sites for water adsorption. The glass-ceramic prepared at 450 °C for 24 h shows the best humidity-sensing performance among all samples, showing an increase in proton conductivity for more than seven orders of magnitude with the increase in relative humidity from 0% to 95%. Under a highly humid atmosphere (95% relative humidity and 25 °C), the proton conductivity of this glass-ceramic reaches 5.2 × 10-3 (Ω cm)-1. Moreover, the electrical response of these materials on the change in the relative humidity is linear and reversible in the entire range of the relative humidity, which indicates that they are novel promising candidates for application as humidity sensors.
Over the last decade, zirconia (ZrO2)-based ceramic materials have become more applicable to modern dental medicine due to the sustained development of diverse computer-aided design/computer-aided manufacturing (CAD/CAM) systems. However, before the cementation and clinical application, the freshly prepared zirconia material (e.g., crowns) has to be processed by sandblasting in the dental laboratory. In this work, the impact of the sandblasting on the zirconia is monitored as changes in morphology (i.e., grains and cracks), and the presence of impurities might result in a poor adhesive bonding with cement. The sandblasting is conducted by using Al2O3 powder (25, 50, 110 and 125 µm) under various amounts of air-abrasion pressure (0.1, 0.2, 0.4 and 0.6 MPa). There has been much interest in both the determination of the impact of the sandblasting on the zirconia phase transformations and conductivity. Morphology changes are observed by using Scanning Electron Microscope (SEM), the conductivity is measured by Impedance Spectroscopy (IS), and the phase transformation is observed by using Powder X-Ray Diffraction (PXRD). The results imply that even the application of the lowest amount of air-abrasion pressure and the smallest Al2O3 powder size yields a morphology change, a phase transformation and a material contamination.
In this study, two different dental ceramics, based on zirconia-reinforced lithium-silicate (LS1) glass-ceramics (Celtra Duo, Dentsply Sirona, Bensheim, Germany) and lithium disilicate (LS2) ceramics (IPS e.max CAD, Ivoclar, Vivadent, Schaan, Liechtenstein) were examined. They were tested prior to and after the crystallization by sintering in the dental furnace. Additionally, the impact of ageing on ceramic degradability was investigated by immersing it in 4% acetic acid at 80 °C for 16 h. The degradability of the materials was monitored by Impedance Spectroscopy (IS), X-Ray Powder Diffraction (XRPD), and Field Emission Scanning Electron Microscope (FE-SEM) techniques. It was detected that LS2 (vs. LS1) samples had a lower conductivity, which can be explained by reduced portions of structural defects. XRPD analyses also showed that the ageing increased the portion of defects in ceramics, which facilitated the ion diffusion and degradation of samples. To summarize, this study suggests that the non-destructive IS technique can be employed to probe the ageing properties of the investigated LS1 and LS2 ceramics materials.
Cation distribution between tetrahedral and octahedral sites within the ZnMn2O4 spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%-19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacity for as-prepared ZnMn2O4 is 909 mAh g-1, while ZnMn2O4 heat-treated at 300 °C is 1179 mAh g-1, which amounts to 101% of its initial capacity. Despite the excellent performance of a sample processed at 300 °C at lower charge/discharge rates (100 mAh g-1), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene-oxide wrapping: the specific capacity obtained after the 400th cycle for graphene-oxide-wrapped ZnMn2O4 heat-treated at 300 °C is 799 mAh g-1 at a charge/discharge rate 0.5 A g-1, which is higher by a factor of 6 compared to samples without graphene -oxide wrapping.
Knowledge about the microstructure is crucial in targeted synthesis of novel nanomaterials. The microstructural parameters, crystallite size and crystallite strain play a major role in physical and chemical properties of the material. X-ray diffraction (XRD) is a very suitable method for this task, since it is non-destructive and it enables a very quick and precise determination of these parameters. The main problem lies in the case where the two neighboring diffraction profiles overlap each other. Here we present a new method for the separation of the overlapping profiles based on the differentiation of the profiles. Further, this method is appropriate for non-crystallographers working in the field of material science since it does not require any crystallographic experience and the full knowledge about the structure of the sample investigated. The microstructural results obtained by the proposed method are very accurate.
The anticholinergic agent oxitropium bromide possesses rich crystal chemistry, most remarkably exhibiting a strong thermosalient effect ("jumping crystal" effect), a mechanical property with potential applications in organic-based actuators. The thermosalient effect, manifested in forceful jumps of up to several centimeters, was investigated by a combination of structural, microscopic, spectroscopic, and thermoanalytical techniques, providing data on which to base a proposed mechanism for the phenomenon. Direct observation of the effect in a single crystal and structure determination of both phases revealed that the jumping of the crystals is a macroscopic manifestation of a highly anisotropic change in the cell volume. The cell distortion is accompanied by a conformational change of the oxitropium cation, which triggers increased separation between the ion pairs in the lattice at nearly identical separation between the cation and the anion within each ion pair. At the molecular level, the cation acts as a molecular shuttle composed of two rigid parts (epoxy-aza-tricyclic-nonyl portion and phenyl ring) that are bridged by a flexible ester linkage. The structure of the rigid, inert aza-tricyclic portion remains practically unaffected by the temperature, suggesting a mechanism in which the large, thermally accumulated strain is transferred over the ester bridge to the phenyl ring, which rotates to trigger the phase transition. Mechanistic details of the higher temperature solid-state phenomena are also presented. The high-temperature phase can also be obtained by grinding or UV irradiation of the room-temperature phase. In addition, if it is irradiated with UV light in the presence of KBr, the high-temperature phase undergoes intramolecular photochemical rearrangement. Heating the high-temperature phase to slightly below the melting temperature results in an additional solid-state reaction that results in the conversion of the salt to a mixture of neutral compounds.
Cholinergic Antagonists/chemistry , Scopolamine Derivatives/chemistry , Calorimetry, Differential Scanning , Crystallography, X-Ray , Hot Temperature , Ultraviolet Rays
Spontaneous precipitation of calcium carbonate was investigated in two precipitation systems: (1) with initial supersaturation lower than that corresponding to the solubility of amorphous calcium carbonate (ACC), at which vaterite precipitated, and (2) with initial supersaturation higher than that of ACC solubility, at which a mixture of calcite and vaterite was formed. After the addition of an acidic polypeptide, poly-L-glutamic acid (pGlu) or poly-L-aspartic acid (pAsp), into (1) a significant inhibition of nucleation, expressed as an increase in induction time, and growth of vaterite, perceived as a dead zone, was observed. Extent of inhibition decreased in the order: Inh(pAps)>Inh(pGlu)>>Inh(pLys). The addition of a polypeptide into (2) caused the inhibition of precipitation and changed the morphology and polymorphic composition of the precipitate; only vaterite appeared at approximately c(pAsp)=3 ppm, c(pGlu)=6 ppm, or c(pLys)=7 ppm. This finding is explained as a consequence of kinetic constraints through the inhibition of calcite nucleation and stronger binding of acidic polypeptide by the calcite surfaces than by the vaterite surfaces. Laboratory precipitation studies using conditions that resemble those in living organism should be run at an initial supersaturation corresponding to the solubility of ACC as a limiting condition.
Amino Acids/chemistry , Calcium Carbonate/chemistry , Polymers/chemistry , Chemical Precipitation , Spectroscopy, Fourier Transform Infrared , Static Electricity
The magnetization processes in binary magnetic/non-magnetic amorphous alloy Hf(57)Fe(43) are investigated by the detailed measurement of magnetic hysteresis loops, temperature dependence of magnetization, relaxation of magnetization and magnetic ac susceptibility, including a nonlinear term. Blocking of magnetic moments at lower temperatures is accompanied by the slow relaxation of magnetization and magnetic hysteresis loops. All of the observed properties are explained by the superparamagnetic behaviour of the single domain magnetic clusters inside the non-magnetic host, their blocking by the anisotropy barriers and thermal fluctuation over the barriers accompanied by relaxation of magnetization. From magnetic viscosity analysis based on thermal relaxation over the anisotropy barriers it is found that magnetic clusters occupy the characteristic volume from 25 up to 200 nm(3). The validity of the superparamagnetic model of Hf(57)Fe(43) is based on the concentration of iron in the Hf(100-x)Fe(x) system that is just below the threshold for long range magnetic ordering. This work also throws more light on the magnetic behaviour of other amorphous alloys.
