Inside the failure mechanism of tin oxide as anode for sodium ion batteries

The conversion-alloying compounds have been identified as promising anode materials for sodium ion batteries (SIBs). One of them, SnO2, with an enormous theoretical capacity of 1558 mAh g−1 is an interesting candidate, also due to its low cost, environmental friendliness and wide availability of tin. However, many drawbacks limit its application in commercial batteries. In this paper, SnO2 has been synthesized from cheap reagents by using simple and easily scalable coprecipitation synthesis routes obtaining nanoparticles with sizes between 2 and 14 nm with almost spherical morphologies. The reasons of the failure of the alloying/de-alloying process were investigated by combining the results obtained from common electrochemical techniques, providing useful examples for the investigation of every material with analogous electrochemical features. Thanks to cyclic voltammetry, different reaction paths were detected for the two samples. The first cycle irreversibility was well characterized with electrochemical impedance spectroscopy, showing interesting trends in the values of the resistance. Galvanostatic cycling with potential limitations was employed to quantify the irreversibility, finding out that the most crystalline sample reached the terminal phase in the Sn-Na system (Na15Sn4), while the least crystalline sample could not achieve such a result (Na3Sn). The crystallinity of SnO2 was determined to be a key parameter, often neglected, for the realization of satisfactory anode compounds.

Intercalated 2D+2D hydrogen-bonded sheets in co-crystals of cobalt salt with 1H,1′H-[3,3′]bipyridinyl-6,6′-dione

Co-crystals of Co(II) salt and 1H,1′H-[3,3′]bipyridinyl-6,6′-dione 1 with the composition 1·Co(CHOO)2(H2O)4 were obtained by mixing both reactants. The single-crystal structure reveals that the metal salt and organic ratio is 1:1. The supramolecular organization of the two components in the co-crystal was mainly dictated by hydrogen bonds between 1 and Co(II) complex. Infrared and powder X-ray diffraction were used to confirm the homogeneity and the phase purity of the bulk crystalline sample of 1·Co(CHOO)2(H2O)4. TGA/DTA was recorded to evaluate the thermal stability of the co-crystals.

Design for multi-step mechanochromic luminescence property by enhancement of environmental sensitivity in a solid-state emissive boron complex

The solid-state emissive boron complex with multi-step mechanochromic luminescence was designed. The crystalline sample showed gradual changes in luminescent color triggered by scratching. The design concept is illustrated.

Frequency analysis for modulation-enhanced powder diffraction

Periodic modulation of external conditions on a crystalline sample with a consequent analysis of periodic diffraction response has been recently proposed as a tool to enhance experimental sensitivity for minor structural changes. Here the intensity distributions for both a linear and nonlinear structural response induced by a symmetric and periodic stimulus are analysed. The analysis is further extended for powder diffraction when an external perturbation changes not only the intensity of Bragg lines but also their positions. The derived results should serve as a basis for a quantitative modelling of modulation-enhanced diffraction data measured in real conditions.

Characteristics of TlBr single crystals grown using the vertical Bridgman-Stockbarger method for semiconductor-based radiation detector applications

TlBr single crystals grown using the vertical Bridgman-Stockbarger method were characterized for semiconductor based radiation detector applications. It has been shown that the vertical Bridgman-Stockbarger method is effective to grow high-quality single crystalline ingots of TlBr. The TlBr single crystalline sample, which was located 6 cm from the tip of the ingot, exhibited lower impurity concentration, higher crystalline quality, high enough bandgap (>2.7 eV), and higher resistivity (2.5 × 1011 Ω·cm) which enables using the fabricated samples from the middle part of the TlBr ingot for fabricating high performance semiconductor radiation detectors.

MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF CONSOLIDATED NANO- AND MICRON- SIZE Cu POWDERS

In this paper, nano-crystalline Cu powder with a mean crystallite size of 45 nm and commercial micron-size Cu powder were either hot pressed or cold pressed and sintered conventionally to fabricate bulk samples. Hardness, density, crystallite size and microstructure of the samples after consolidation were examined. The results show that the hardness of the hot pressed nano-crystalline Cu is in the range of 0.75-1.2 GPa which is higher than that of commercial Cu . The density of the bulk nano-crystalline sample showed that the rising sintering temperature increases the density up to 97% of the theoretical value. The mean crystallite size of the hot pressed sample was 64 nm, which still was in the nano scale. The scanning electron microscopy (SEM) images revealed that the hot pressed samples contain less porosities compared to the conventionally consolidated samples.

VORTEX CREEP PERPENDICULAR TO THE c-AXIS IN CRYSTALLINE AND GRAIN-ORIENTED YBCO SUPERCONDUCTOR

Magnetization measurements were carried out on crystalline and grain-oriented YBa 2 Cu 3 O 7-δ samples. We have measured the creep of magnetic flux lines along the a-axis (perpendicular to the c-axis) of the crystalline sample and perpendicular to the c-axis of a c-axis-grain-oriented polycrystalline sample. The measurements were done at 4.2 K and for magnetic fields in the range 1 kOe < H < 10 kOe . The magnetization M was found to decrease linearly with ln t in both samples for all the applied magnetic fields. With the initial increase of the applied magnetic field, the vortex pinning potential, Up, was found to decrease sharply in the grain-oriented sample, followed by a slow (almost linear) rate of decrease. In the crystalline sample, the rate of decrease of Up was found to be slow and linear for all applied magnetic fields.

Preparation and Investigation on Magneto-Electric Effect of Cr2O3 Thin Films

We investigated the magneto-electric properties and electric properties of Cr2O3 thin films. Cr2O3 thin films were prepared on a thermal-oxidized Si substrate and a c-Al2O3 substrate. The sample prepared on the thermal-oxidized Si substrate had poly-crystalline structure. On the other hand, the sample prepared on the c-Al2O3 substrate has preferentially (006) oriented structure. Both samples had high enough resistivity to get a high induced magnetic moment. The induced magnetic moment by applying external voltage was observed on the oriented sample, although there was no induced magnetic moment on the same voltage for the poly-crystalline sample. This difference may be due to the random distribution of crystal and the leakage current caused by the Pool-Frenkel type defect in the poly-crystalline film.