Effect of Cr-doping on the physicochemical properties of blue TiO2 and its application in dye-sensitized solar cells via low-temperature fabrication process

Cr-doped blue TiO₂ (Cr-BTiO₂) nanoparticles were fabricated at room temperature using lithium-ethylenediamine (Li-EDA) as reducing agent. The addition of Li-EDA promotes the selective reduction of the rutile phase of TiO₂ into the amorphous phase keeping anatase phase unaltered. Hence, the phase-selective reduction of TiO₂ leads to the formation of blue TiO₂ nanoparticles. Synthesized samples were characterized by equipment fitted with modern technology. The shifting of (101) peak to a lower angle (2θ) in Cr-BTiO₂ in X-ray diffraction (XRD) pattern suggests the successful doping of chromium into TiO₂ lattices. In Raman spectra, the shifting of the active Eg peak of Cr-BTiO₂ nanoparticles to higher wavenumber also suggests the successful substitution of Ti by Cr. The blue TiO₂ and Cr-BTiO₂ show increased absorption of light in the visible region compared to TiO₂ (P25). The modified TiO₂ samples have improved electron-hole separation tendency as predicted by the photoluminescence spectra (PL). Also, doping of Cr- into TiO₂ lattice results the formation of oxygen vacancy as detected by X-ray photoelectron spectroscopy (XPS). Among all samples, Cr-BTiO₂ demonstrated improvement in J_sc and overall incident photon to current conversion efficiency. Therefore, the synthetic effect is thus responsible for the enhancement in efficiency of Cr-BTiO₂ towards the dye-sensitized solar cell (DSSC) by 2.5 and 1.5 times higher than the P25 and blue TiO₂, respectively.     

Effect of Pulse and Direct Current Electrodeposition on Microstructure,Surface,and Scratch Resistance Properties of Ni-W Alloy and Ni-W-SiC Composite Coatings

The present work aims to study the influence of direct current and pulse current techniques as well as embedded SiC nanoparticles on the mechanical properties of the electrodeposited Ni-W coating. The electrodeposited coatings were studied for morphological, microstructural, mechanical, and scratch resistance properties using the surface roughness tester, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Vickers microhardness, and scratch tester. Application of pulse current exhibited relatively homogeneous and smooth surface of the coatings. A remarkable increment of microhardness was observed in both Ni-W and Ni-W-SiC coatings prepared under pulse current as compared to the direct current technique. Similarly, the scratch test revealed a considerable improvement in the scratch resistance behavior of the Ni-W alloy and the composite coatings from the pulsed current condition. Hence, the application of pulse current not only improved the surface- and microstructure-related properties but also enhanced the Vickers microhardness and scratch resistance properties of the coatings. In addition, the reduction in micro-cracks revealed the improvement in scratch resistance properties of the coatings due to the incorporated SiC nanoparticles into the Ni-W alloy matrix.     

Nonequilibrium Dynamics of a Bose-Einstein Condensate Excited by a Red Laser Inside a Power-Law Trap with Hard Walls

We explore the nonequilibrium dynamics of a two-dimensional trapped Bose-Einstein condensate excited by a moving red-detuned laser potential. The trap is a combination of a general power-law potential cutoff by a hard wall box potential. The red laser potential is allowed to exit the box potential, leaving the system in a highly nonequilibrium state. This is crucial since the red laser potential squeezes the BEC trapped inside it against the hard wall-boundary at this instant, paving the way for the creation of a shock wave. Once the red laser potential has left the box potential, the Hamiltonian of the system becomes time-independent and the total energy stabilizes. Our systems are simulated by the time-dependent Gross-Ptiaevskii Equation which is numerically solved by the split-step Crank-Nicolson method in real time. It is found that the value at which the total energy stabilizes in the transient stage of the simulation is largely controlled by the initialization process. Before the red laser potential leaves the trap, when the Hamiltonian of the system is still time-dependent, oscillations in the total energy occur if the system is initialized adiabatically by application of a gradually growing and moving red laser potential. If this laser potential is not moving, yet fully present in the initialization process, these oscillations are not observed in the transient stage of the simulation. In addition, the system displays oscillations in the root-mean-square radius of the trapped cloud. The amplitudes of these radial oscillations continue even after the red laser potential leaves the box potential and are used to explore the deviation of the nonstationary states from the corresponding ground states. It is demonstrated that the geometry of the power law potential influences the amplitude of these radial oscillations, reducing them and bringing the systems closer to an equilibrium state. We then argue that by going to tighter trapping geometries, it is not possible to achieve a completely stable system which has been earlier excited by a red laser potential. Most importantly, an increase in the curvature of the power law trap results in chaotic oscillations of the cloud. This work should stimulate further experiments exploring the extent of the nonequilibrium states by a measurement of the amplitude of the root-mean-square radial oscillations of the trapped cloud.