Intrinsic properties of high -aspect ratio single- and double -wall anodic TiO 2 nanotube layers annealed at different temperatures

TiO2 nanotube layers of different thicknesses and tube wall morphologies exploited. Single-wall nanotubes were obtained by chemical etching of double-wall ones. Photocurrents, structure, optical and electronic properties of tubes were compared

ALD growth of MoS2 nanosheets on TiO2 nanotube supports

Two-dimensional MoS2 nanostructures are highly interesting and effective in a number of energy-related applications. In this work, the synthesis of ultra-thin MoS2 nanosheets produced by the thermal Atomic Layer Deposition (ALD) process is reported for the first time using a previously unpublished set of precursors, namely bis(t-butylimido)bis(dimethylamino)molybdenum and hydrogen sulfide. These nanosheets are homogenously deposited within one-dimensional anodic TiO2 nanotube layers that act as a high surface area conductive support for the MoS2 nanosheets. The decoration of high aspect ratio TiO2 nanotube layers with MoS2 nanosheets over the entire nanotube layer thickness is shown for the first time. The homogeneous distribution of the MoS2 nanosheets is proved by STEM/EDX. This resulting new composite is employed as anode for Li-ion microbatteries. The MoS2-decorated TiO2 nanotube layers show a superior performance compared to their counterparts without MoS2. Compared to electrochemical performance of pristine TiO2 nanotube, a more than 50% higher areal capacity and a coulombic efficiency of 98% are obtained on the MoS2 decorated TiO2 nanotube layers, demonstrating clear synergic benefits of the new composite structure

Indometacin: Vzájemný vztah mezi strukturní relaxací, viskózním tokem a krystalovým růstem

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size (d(aver)) and heating rate (q(+)) on the structural relaxation, crystal growth and decomposition kinetics of amorphous indomethacin. The structural relaxation and decomposition processes exhibited d(aver)-independent kinetics, with the q(+) dependences based on the apparent activation energies of 342 and 106 kJ center dot mol(-1), respectively. The DSC-measured crystal growth kinetics played a dominant role in the nucleation throughout the total macroscopic amorphous-to-crystalline transformation: the change from the zero-order to the autocatalytic mechanism with increasing q(+), the significant alteration of kinetics, with the storage below the glass transition temperature, and the accelerated crystallization due to mechanically induced defects. Whereas slow q(+) led to the formation of the thermodynamically stable gamma polymorph, fast q(+) produced a significant amount of the metastable alpha polymorph. Mutual correlations between the macroscopic and microscopic crystal growth processes, and between the viscous flow and structural relaxation motions, were discussed based on the values of the corresponding activation energies. Notably, this approach helped us to distinguish between particular crystal growth modes in the case of the powdered indomethacin materials. Ediger's decoupling parameter was used to quantify the relationship between the viscosity and crystal growth. The link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model and microscopic crystal growth was proposed.Neizotermní DSC studie vlivu velikosti částic a rychlosti krystalizace na strukturní relaxaci, růst krystalů a rozkladnou kinetiku amorfního indometacinu byla provedena. Strukturní relaxace a rozkladný proces vykazují kinetiku nezávislou na průměru částic. V kinetice růstu má dominantní roli nukleace, která významně mění kinetický mechanismus. Dále se uplatňuje vliv mechanicky indukovaných nukleí a skladování při teplotách pod skelným přechodem.

Strukturální metastabilita v chalkogenidových polovodičích: Úloha chemických vazeb

This article reviews metastability in three different classes of chalcogenides-chalcogenide glasses, phase-change alloys, and transition-metal dichalcogenides-with the focus on the relationship between structural metastability and the nature of chemical bonding. While the presence of lone-pair electrons in chalcogenide glasses enables a variety of bond switching processes, the existence of resonant (metavalent) bonding in phase-change alloys is key to the transformation between the crystalline and amorphous states. Strong covalent bonds in 2D transition-metal dichalcogenides limit the transformation to slides and buckling of atomic planes without major bond rupture. It is proposed that combining different kinds of local bonding may be an efficient way to engineer amorphous chalcogenides with desired properties.Tento článek hodnotí metastabilitu ve třech různých třídách chalkogenidů - chalkogenidových skel, slitin s fázovými změnami a dichalkogenidů přechodných kovů - se zaměřením na vztah mezi strukturní metastabilitou a povahou chemické vazby. Zatímco přítomnost volných elektronových párů v chalkogenidových sklech umožňuje řadu procesů přepínání vazeb, existence rezonanční (metavalentní) vazby ve slitinách s rychlou fázovou přeměnou je klíčovým faktorem k transformaci mezi krystalickým a amorfním stavem. Silné kovalentní vazby ve 2D dichalkogenidech přechodných kovů omezují transformaci mezi rovnými a “cik-cak” atomovými rovinami bez většího prasknutí vazeb. Navrhujeme, že kombinace různých druhů lokálních vazeb může být účinným způsobem, jak připravit amorfní chalkogenidy s požadovanými vlastnostmi

Příprava keramiky a sklokeramiky na bázi Sb2Se3 z původních tenkých filmů nanesených na Kaptonové fólii

Amorphous Sb2Se3 thin films (200-1500 nm) deposited on Kapton foil were crystallized in controlled environment using the method of direct calorimetric measurement of thin films. X-ray diffraction was used to determine the intensity of the 1D (Sb4Sb6)n ribbons preferential orientation in dependence on the processing conditions: film thickness, energy flux during the pulsed laser deposition (PLD), heating rate, low and high temperature annealing. Lower PLD energy flux combined with higher deposited film thickness (1500 nm) led to increased orientation in the [2 2 1] direction, which is favorable for thin film solar cells application. Raman spectroscopy showed that thermally induced crystallization produces oxide-free Sb2Se3 thin films. Description of the crystallization kinetics led to very accurate kinetic predictions for the isothermal annealing conditions suitable for preparation of glass-ceramics with defined amount of crystalline phase - the predictions were accurate to ~10% of the true (experimentally determined) value.Amorfní tenký film Sb2Se3 na Kaptonové fólii byl krystalizován za kontrolovaných podmínek pomocí kalorimetru. Zkoumání metodou XRD ukázalo intenzivní pás 1D (Sb4Sb6)n s preferenční orientací v závislosti na podmínkách. Ramanova spektroskopie odhalila volným kyslíkem indukovanou krystalizaci Sb2Se3 filmu. Popis krystalizace vede k přesné kinetické predikci během izotermního zpracování a přípravě sklokeramiky s definovaným množstvím krystalické fáze

Dielectric Performance of Natural- and Synthetic-Ester-Based Nanofluids with Fullerene Nanoparticles

According to the latest research, nanofluids as a possible future substitution for high-voltage equipment insulation have the potential to enhance the heat transfer and insulation properties of their base fluids. Dielectric properties are represented by breakdown strength (AC, DC, lightning) and dielectric performance as a set of quantities including dissipation factor, permittivity, and volume resistivity. In this study, natural and synthetic esters were mixed with C60 nanoparticles. Samples were examined for dissipation factor, relative permittivity, and volume resistivity at temperatures between 25 °C and 140 °C to monitor changes in dielectric performance with rising temperature, in accordance with IEC 60247. In addition, the samples were tested for AC breakdown voltage (using mushroom-like electrodes with a gap distance of 1 mm) and evaluated using the Weibull distribution statistical method. These measurements allowed complex evaluation of the examined mixtures and the determination of optimal concentration for each ester-based nanofluid

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0–100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass–crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0–100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass–crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors