Modification of dielectric relaxations in sodium bismuth titanate with samarium doping

Na_0.5Bi_(0.5−x) Sm_xTiO₃ (NBST) ceramics with x=0.05, 0.1, and 0.15 are prepared through chemical route. The X-ray diffraction studies confirmed the formation of single phase. Dielectric measurements in the temperature region ranging from room temperature (∼30 °C) to 600 °C at different frequencies (10 kHz-1 MHz) showed anomalies at 130, 306, and 474 °C (at 10 kHz frequency) for x=0.05 sample. Other samples showed only two peaks. To establish the electrical nature of these relaxations, impedance measurements are done at different temperatures and frequencies. The relaxation time, obtained from both impedance and modulus data, is found to decrease with increase in temperature. The relaxations observed are of non-Debye type. Increase in samarium content increases the activation energy for relaxation.     

A rapid and highly efficient Michael addition of methoxybenzenes and indoles to α,β-unsaturated ketones using BF3·OEt2 as a catalyst

An efficient and general protocol is described for the Michael addition of α,β-unsaturated ketones with electron-rich arenes/indoles to give alkylated arenes/indoles under mild reaction condition at room temperature. Shorter reaction time, convenient and good isolated yields are the significant features of this protocol. Moreover, the procedure is environmentally benign in nature and applicable to variety of arenes/indoles as well as α,β-unsaturated ketones.     

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo‐Polymerization Reaction

Getting suitable crystals for single‐crystal X‐ray crystallographic analysis still remains an art. Obtaining single crystals of metal–organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single‐crystal‐to‐single‐crystal manner. The spacer ligands with trans,trans,trans‐conformation in the pillared‐layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans‐conformation prior to [2+2] photo‐cycloaddition reaction and yield single crystals of MOF containing two‐dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.     

I2–DMSO promoted intramolecular oxidative cyclization of 2-(aryl or alkyl amino)-acetophenones for the synthesis of isatins

An I₂–DMSO promoted novel and efficient method is described for the synthesis of isatins from 2-aminoaryl methyl ketone. A series of alkyl or aryl isatin derivatives were successfully synthesized under the optimized reaction conditions.     

Synthesis and magnetic properties of NiFe2−xAlxO4 nanoparticles

Nanocrystalline Al-doped nickel ferrite powders have been synthesized by sol–gel auto-ignition method and the effect of non-magnetic aluminum content on the structural and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with inverse spinel structure. The calculated grain sizes from XRD data have been verified using transmission electron microscopy (TEM). TEM photographs show that the powders consist of nanometer-sized grains. It was observed that the characteristic grain size decreases from 29 to 6 nm as the non-magnetic Al content increases, which was attributed to the influence of non-magnetic Al concentration on the grain size. Magnetic hysteresis loops were measured at room temperature with a maximum applied magnetic field of ≈1 T. As aluminum content increases, the measured magnetic hysteresis curves become more and more narrow and the saturation magnetization and remanent magnetization both decreased. The reduction of magnetization compared to bulk is a consequence of spin non-collinearity. Further reduction of magnetization with increase of aluminum content is caused by non-magnetic Al³⁺ ions and weakened interaction between sublattices. This, as well as the decrease in hysteresis was understood in terms of the decrease in particle size.     

Recent Progress and Emerging Applications of Rare Earth Doped Phosphor Materials for Dye‐Sensitized and Perovskite Solar Cells: A Review

Although the efficiency of Dye‐sensitized and Perovskite solar cell is still below the performance level of market dominance silicon solar cells, in last few years they have grabbed significant attention because of their fabrication ease using low‐cost materials, and henceforth these cells are considered as a promising alternative to commercial photovoltaic devices. However, third generation solar cells have significant absorption in the visible region of solar spectrum, which confines their power conversion efficiency. Subsequently, the performance of current photovoltaics is significantly hampered by the transmission loss of sub‐band‐gap photons. To overcome these issues, rare earth doped luminescent materials is the favorable route followed to convert these transmitted sub‐band‐gap photons into above‐band‐gap light, where solar cells typically have significant light‐scattering effects. Moreover, the rare earth based down/up conversion material facilitates the improvement in sensitization, light‐scattering and device stability of these devices. This review provides insight into the application of various down/up conversion materials for Dye‐sensitized and perovskite solar cell applications. Additionally, the paper discusses the techniques to improve the photovoltaic performance in terms of current density and photo voltage in detail.     

Voltage- and Power-Conversion Performance of Bi-functional ZrO2 : Er3+/ Yb3+ Assisted and Co-sensitized Dye Sensitized Solar Cells for Internet of Things Applications

Giant power conversion efficiency is achieved by using bifunction ZrO₂ : Er³⁺/Yb³⁺assisted co-sensitised dye-sensitized solar cells. The evolution of the crystalline structure and its microstructure are examined by X-ray diffraction, scanning electron microscopy studies. The bi-functional behaviour of ZrO₂ : Er³⁺/Yb³⁺ as upconversion, light scattering is confirmed by emission and diffused reflectance studies. The bi-function ZrO₂ : Er³⁺/Yb³⁺ (pH=3) assisted photoanode is co-sensitized by use of N719 dye, squaraine SPSQ2 dye and is sandwiched with Platinum based counter electrode. The fabricated DSSC exhibited a giant power conversion efficiency of 12.35 % with V_OC of 0.71 V, J_SC of 27.06 mA/cm², FF of 0.63. The results, which motivated the development of a small DSSC module, gave 6.21 % and is used to drive a tiny electronic motor in indoor and outdoor lighting conditions. Small-area DSSCs connected in series have found that a V_OC of 4.52 V is sufficient to power up Internet of Things (IoT) devices.     

Synchronization and suppression of chaos in non-locally coupled map lattices

We considered coupled map lattices with long-range interactions to study the spatiotemporal behaviour of spatially extended dynamical systems. Coupled map lattices have been intensively investigated as models to understand many spatiotemporal phenomena observed in extended system, and consequently spatiotemporal chaos. We used the complex order parameter to quantify chaos synchronization for a one-dimensional chain of coupled logistic maps with a coupling strength which varies with the lattice in a power-law fashion. Depending on the range of the interactions, complete chaos synchronization and chaos suppression may be attained. Furthermore, we also calculated the Lyapunov dimension and the transversal distance to the synchronization manifold.