Origin of Hole-Trapping States in Solution-Processed Copper(I) Thiocyanate (CuSCN) and Defect-Healing by I2_2 Doping

Solution-processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short-range order; the defects result in a high density of trap states that limit the device performance. Despite the extensive electronic applications of CuSCN, its defect properties have not been studied in detail. Through X-ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide-based recipe is found to contain under-coordinated Cu atoms, pointing to the presence of SCN vacancies. A defect passivation strategy is introduced by adding solid I$_2$ to the processing solution. At small concentrations, the iodine is found to exist as I$^-$ which can substitute for the missing SCN$^-$ ligand, effectively healing the defective sites and restoring the coordination around Cu. Applying I$_2$-doped CuSCN as a p-channel in thin-film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I$_2$ doping method leads to the defect healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance-voltage characteristics corroborates that the trap state density is reduced upon I$_2$ addition. The contact resistance and bias-stress stability of the devices also improve. This work shows a simple and effective route to improve hole transport properties of CuSCN which is applicable to wide-ranging electronic and optoelectronic applications

Study of Microstructure and Mechanical Properties of Commercially Pure Sn and Sn-4%Bi Alloys Fabricated by Permanent Mold Gravity Casting and Forging

The influences of 4 wt% bismuth addition and room temperature strain on microstructure and mechanical properties in tin alloys were investigated in this study. Commercially pure tin and Sn-4%Bi alloys were fabricated by permanent mold gravity casting. The samples were then subjected to forging process at room temperature. As-cast microstructures were compared with 0.25 and 0.5 strained samples. Differential Scanning Calorimetry (DSC) was used to confirm the effect of bismuth on undercooling. The recrystallization and grain growth processes were confirmed by grain size distribution and misorientation study using Electron Backscattered Diffraction (EBSD). Furthermore, position and morphology of the bismuth precipitates were investigated by using Field Emission Scanning Electron Microscope (FESEM). X-ray Photoelectron Spectroscopy (XPS) revealed that tin oxide was the main species found on the surface of these alloys. There was no evidence of bismuth oxide on the surface. Furthermore, the Hall-Petch hardness approximation analysis revealed that there were other influences, which increased the hardness beyond the grain refinement effect

Kinetics of Catalytic Oxidation of Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over LaMn1-xNixO3-d Perovskite Oxide

This present research aims at studying the kinetic reaction of HMF oxidation which is influenced by temperature gradient and Mn/Ni cation ratio in a lanthanum-based perovskite oxide catalyst. The result can be a fruitful database for the further development of the semi-industrial FDCA derivatives production process. Three Mn/Ni cation ratios of LaMnO3-d, LaMn0.5Ni0.5O3-d, and LaNiO3-d catalysts were selected and prepared by the Sol-Gel method. The bulk chemical species and oxidation states of secondary metal elements (Mn and Ni) for all synthesized perovskite-oxide catalysts were characterized by X-ray absorption near edge structure (XANES). The result of the distinct ratio of Mn3+/Mn4+ ions significantly affected the oxidation reaction of HMF. The LaMn0.5Ni0.5O3-d and LaMnO3-d catalysts achieved high catalytic performance for the HMF oxidation reaction at 120 °C for 4 hrs. The kinetic parameters and activation energy were successfully estimated and reported

The role of Ce addition in catalytic activity enhancement of TiO2-supported Ni for CO2 methanation reaction

In this work, various amounts of Ce were added to TiO2 to form a mixed oxide support; CexTi1−xO2 (x = 0, 0.003, 0.05, 0.10 and 0.15) and then those synthesized supports were impregnated by 10 wt% Ni to produce a catalysts. The 10 wt% Ni–CexTi1−xO2 (x = 0, 0.003, 0.05, 0.10 and 0.15) catalysts were tested for CO2 methanation reaction by using a fixed-bed reactor in the temperature range of 100–500 °C. The sample was pretreated at 450 °C under H2 and then a mixed feed gas of CO2 and H2 was switched into the reactor to start the reaction. The results showed that 10 wt% Ni–Ce0.003Ti0.997O2 catalyst (the lowest Ce content) exhibited the highest CO2 conversion and CH4 yield. Moreover, 10 wt% Ni–Ce0.003Ti0.997O2 showed highly stable during the stability test (50 h.). The results indicated that upon addition of small amount of Ce into TiO2-supported Ni, the surface, structural, electrical and redox properties of the catalyst were improved to the extent that these properties can promote the catalytic activities for CO2 methanation. The Ce addition can improve the CO2 methanation catalytic activity by several ways. First, higher dispersion of Ni on catalysts surface upon addition of Ce was observed which resulted in higher adsorption rate of H2 on this metal active site. Second, formation of a larger amounts of oxygen vacancies as well as basicity improvement upon addition of Ce were occurred which can increase the CO2 adsorption on catalyst surface. Third, incorporation of Ce resulted in improving of a starting reduction temperature of Ni2+ to Ni0 for TiO2-supported Ni catalyst which can indicate that the reducibility of Ce-doped TiO2-supported Ni catalyst was enhanced and then alter its catalytic activity. However, increasing of Ce content led to lowering of CO2 methanation activities which resulted from increasing of basicity by Ce addition. The excess amounts of adsorbed CO2 would lead to competitive adsorption to H2 and then lead to a decrease of catalytic activity. Therefore, an appropriate amount of H2 and CO2 adsorption ability on catalyst surface was a prominent factor to dominate the catalytic activity

Hydrogen-Bonding Interactions in Hybrid Aqueous/Nonaqueous Electrolytes Enable Low-Cost and Long-Lifespan Sodium-Ion Storage.

Although "water-in-salt" electrolytes have opened a new pathway to expand the electrochemical stability window of aqueous electrolytes, the electrode instability and irreversible proton co-insertion caused by aqueous media still hinder the practical application, even when using exotic fluorinated salts. In this study, an accessible hybrid electrolyte class based on common sodium salts is proposed, and crucially an ethanol-rich media is introduced to achieve highly stable Na-ion electrochemistry. Here, ethanol exerts a strong hydrogen-bonding effect on water, simultaneously expanding the electrochemical stability window of the hybridized electrolyte to 2.5 V, restricting degradation activities, reducing transition metal dissolution from the cathode material, and improving electrolyte-electrode wettability. The binary ethanol-water solvent enables the impressive cycling of sodium-ion batteries based on perchlorate, chloride, and acetate electrolyte salts. Notably, a Na0.44MnO2 electrode exhibits both high capacity (81 mAh g-1) and a remarkably long cycle life >1000 cycles at 100 mA g-1 (a capacity decay rate per cycle of 0.024%) in a 1 M sodium acetate system. The Na0.44MnO2/Zn full cells also show excellent cycling stability and rate capability in a wide temperature range. The gained understanding of the hydrogen-bonding interactions in the hybridized electrolyte can provide new battery chemistry guidelines in designing promising candidates for developing low-cost and long-lifespan batteries based on other (Li+, K+, Zn2+, Mg2+, and Al3+) systems

Role of Adsorption Phenomena in Cubic Tricalcium Aluminate Dissolution

The workability of fresh Portland cement (PC) concrete critically depends on the reaction of the cubic tricalcium aluminate (C₃A) phase in Ca- and S-rich pH >12 aqueous solution, yet its rate-controlling mechanism is poorly understood. In this article, the role of adsorption phenomena in C₃A dissolution in aqueous Ca-, S-, and polynaphthalene sulfonate (PNS)-containing solutions is analyzed. The zeta potential and pH results are consistent with the isoelectric point of C₃A occurring at pH ∼12 and do not show an inversion of its electric double layer potential as a function of S or Ca concentration, and PNS adsorbs onto C₃A, reducing its zeta potential to negative values at pH >12. The S and Ca <i>K</i>-edge X-ray absorption spectroscopy (XAS) data obtained do not indicate the structural incorporation or specific adsorption of SO₄^2– on the partially dissolved C₃A solids analyzed. Together with supporting X-ray ptychography and scanning electron microscopy results, a model for C₃A dissolution inhibition in hydrated PC systems is proposed whereby the formation of an Al-rich leached layer and the complexation of Ca–S ion pairs onto this leached layer provide the key inhibiting effect(s). This model reconciles the results obtained here with the existing literature, including the inhibiting action of macromolecules such as PNS and polyphosphonic acids upon C₃A dissolution. Therefore, this article advances the understanding of the rate-controlling mechanism in hydrated C₃A and thus PC systems, which is important to better controlling the workability of fresh PC concrete

The structure of rare-earth gallate and aluminium glasses dertermined by neutron and x-ray diffraction and spectroscopy

Recently glasses based on gallate and aluminate networks have aroused interest in laser technology, for example, for the use as the host for .Iaser active ions. As these glasses are not good glass-formers other ingredients such as silica are normally added to improve their glass abilities. In this work I have succeeded in producing these glasses without the need for these additions. The structures of these pure rare-earth gallate and aluminate glasses made by aerodynamic levita- tion and laser heating techniques have been studied including neutron and X-ray diffraction and spectroscopy. The following results have been obtained. The structures of rare-earth gallate glasses, R2Ga6012 and R3Ga5012 where R = Pr and Nd, were studied using neutron diffrac- tion with the isomorphic substitution technique. A good agreement between the structural models from MD simulation and MD-RMC for the difference functions and the full experimental data sets was achieved. The mean Ga-O coordination number was found to be 4.1(1). The results also show a mixture of 6, 7 and 8-fold coordinated sites for the rare-earth ions with an average coordination number of 7.7(1). A more detailed study using a combination of neutron diffraction, Extended X-ray Absorption Fine Structure (EXAFS), MD simulation and MD-RMC refinement was applied to obtain the detail of the local structure of Pr3Ga5012 glasses at Pr and Ga K-edges. The nucleation and phase separation in the (Y203)x(Al203)1-x glassy systems produced by an aerodynamic levitation and laser heating was studied using micro-focus EXAFS. Turbidity was found to occur in the x 0.35 glasses. At x 1μm) were seen in the turbid glasses, a phase separation into a polycrystalline sample of YAP (x = 0.50) and pure alumina was found. It is concluded that the turbidity in glassy samples at x ≤ 0.25 is due to the formation of nano meter size crystallites. For x = 0.36 and 0.375 (known as YAG), a nucleation of YAG crystals as spherical inclusions was found in a glass matrix giving rise to the turbidity in these glasses. Finally, a study of the structures of BaTiAl206 glasses was made in order to understand the processes giving rise to their unusual properties. Black and opaque, and clear and transparent BaTiAb06 glasses produced by aerodynamic levitation and laser heating by fast and slow quench rates were studied. Neutron and X-ray diffraction, MD simulation, MD-RMC refinement and X-ray absorption spectroscopy have been used and combined to determine the structure of the glass especially with regard to the coordination structure around the Ti ions. Evidence is found to show that the Ti ions occur in four fold and higher fold oxygen coordinated sites while the Al ions remain to- tally four fold coordinated. Very small differences in the structure of the two glasses are observed confirming that the opacity arises largely due to a small number of optical defects in present in the same overall glass structure.EThOS - Electronic Theses Online ServiceGBUnited Kingdo