Understanding the depolarization phenomena in (1-x) Na0.5Bi0.5TiO3. (x) Ba0.85Ca0.15Ti0.90Zr0.10O3solid solutions usingin-situtemperature dependent Raman spectroscopy.

A decrease in depolarization temperature (Td) from 456 K to 352 K was observed with an increase in BCZT substitution in the NBT for the (1-x) Na0.5Bi0.5TiO3. (x) Ba0.85Ca0.15Ti0.90Zr0.10O3solid solutions. A transition towards a higher ergodic state was elucidated with an increase in BCZT content that helped to reduce the free energy barrier, hence lesser thermal energy was required to depolarize the modified systems. Furthermore, a decrease in remnant polarization and coercive field, coupled with an increase in energy storage (Wstored) and efficiency (η%) with higher BCZT content.In-situtemperature-dependent Raman spectra provide additional insights, highlighting the faster changes in phonon shifts and lifetimes corresponding to the A-O, B-O, and BO6vibrations around the depolarization temperature (Td). The observed phase transformation to aP4bm phase at temperatures significantly higher thanTdis substantiated by Raman shift and phonon lifetime variations in the modes associated with the A-O and B-O vibrations. The transitions can be understood as: atT∼Tdthe polar nano regions (PNRs) start to appear due to weakening of bonds,T>Tdall the long-range ferroelectric domains transform to PNRs converting the material to a fully ergodic state, and at much higher temperatures (T≫Td) theR3c PNRs vanish andP4bm PNRs appear.

Structural and Surface Properties of pH-Varied Fe2O3 Nanoparticles: Correlation with Antibacterial Properties.

Hematite (Fe2O3) nanoparticles were synthesized using a hydrothermal synthesis route under different pH conditions (pH ∼8,10,11.5) (i.e., different ratios of H+/OH- ions). The sample synthesized at pH 10 had better motility toward the bacterial surface due to having an overall positive charge (ξ-potential = +11.10), leading to a minimal hydrodynamic size (Dτ = 186.6). The results are discussed in light of the relative ratio of H+/OH- that may affect bond formation by influencing the electronic clouds of the participating ions that can modify the structure. This, in turn, modifies crystallinity, strain, disorder, surface termination, and thereby, the surface charge, which has been correlated to the antibacterial properties of the nanoparticles due to the interaction between the respective opposite charges on the nanoparticle surface and bacterial cell wall. The structural modifications were correlated to all of these parameters in this work.

Cluster spin-glass-like dynamics in Mn-rich La2Ni0.5Mn1.5O6ferromagnetic insulator.

We report on the physical properties of Mn-rich, nonstoichiometric La2Ni0.5Mn1.5O6ferromagnetic insulator, prepared by sol-gel method. The single-phase orthorhombicPbnmstructure for the compound was confirmed by x-ray diffraction measurements. Dc magnetization measurements revealed a high saturation magnetization of ∼5.95 µB/f.u. at 5 K, and a ferromagnetic to paramagnetic transition at ∼162 K. Ac magnetic susceptibility measurements confirmed a broad frequency-dependent anomaly at lower temperatures indicating the presence of spin-glass type magnetic interactions. The ac susceptibility data have been discussed within the framework of the critical slowing down model and Vogel-Fulcher law, and confirmed the cluster spin-glass dynamics with a relaxation time of the order of 10-5 s. The valence of Ni and Mn ions was verified from the x-ray absorption near edge structure spectroscopy. The origin of cluster spin-glass state was discussed in terms of several possible magnetic exchange interaction pathways among Ni and Mn ions.

Effect of ionic size compensation by Ag+ incorporation in homogeneous Fe-substituted ZnO: studies on structural, mechanical, optical, and magnetic properties.

Substituting an ion of different size from that of the host element introduces lattice strain and defects. However, this mismatch may be significantly reduced by substituting an additional ion with a compensating size relative to the dopant. Such a double substitution might offer better solubility irrespective of the local distortions as well as the formation of defects in the valence states. Fe-substituted ZnO has been widely reported with conflicting results primarily arising from lack of chemical and structural homogeneity originating from preparation techniques, compositional fluctuations, and equivocal comprehension of actual solubility limits of the dopants. In this study, Ag ion has been incorporated in Fe-substituted ZnO to compensate the ionic size of Zn1-x [Fe0.8Ag0.2] x O (0 ≤ x ≤ 0.03125) by determining the solubility limit of the homogeneous material and their corresponding structural, mechanical, optical and magnetic properties have been investigated thoroughly. Co-substitution rearranges the lattice and leads to better crystal structures with tunable properties related to the amount of substitution.

Exciplex-Forming Cohost for High Efficiency and High Stability Phosphorescent Organic Light-Emitting Diodes.

An exciplex forming cohost system is employed to achieve a highly efficient organic light-emitting diode (OLED) with good electroluminescent lifetime. The exciplex is formed at the interfacial contact of a conventional star-shaped carbazole hole-transporting material, 4,4',4″-tris(N-carbazolyl)-triphenylamine (TCTA), and a triazine electron-transporting material, 2,4,6-tris[3-(1H-pyrazol-1-yl)phenyl]-1,3,5-triazine (3P-T2T). The excellent combination of TCTA and 3P-T2T is applied as the cohost of a common green phosphorescent emitter with almost zero energy loss. When Ir(ppy)2(acac) is dispersed in such exciplex cohost system, OLED device with maximum external quantum efficiency of 29.6%, the ultrahigh power efficiency of 147.3 lm/W, and current efficiency of 107 cd/A were successfully achieved. More importantly, the OLED device showed a low-efficiency roll-off and an operational lifetime (τ80) of ∼1020 min with the initial brightness of 2000 cd/m2, which is 56 times longer than the reference device. The significant difference of device stability was attributed to the degradation of exciplex system for energy transfer process, which was investigated by the photoluminescence aging measurement at room temperature and 100 K, respectively.

Correction: Effect of ionic size compensation by Ag+ incorporation in homogeneous Fe-substituted ZnO: studies on structural, mechanical, optical, and magnetic properties.

[This corrects the article DOI: 10.1039/C8RA02393J.].

Cu1-x Fe x O: hopping transport and ferromagnetism.

Single phase, sol-gel prepared Cu1-x Fe x O (0 ≤ x ≤ 0.125) powders are characterized in terms of structural, electronic and magnetic properties. Using dielectric and magnetic studies we investigate the coupling of electron and spin. The electrical conductivities and activation energies are studied with increasing Fe content. Modelling of experimental conductivity data emphasizes a single hopping mechanism for all samples except x = 0.125, which have two activation energies. Hole doping is confirmed by confirming a majority Fe3+ substitution of Cu2+ in CuO from X-ray photoelectron spectroscopy studies (XPS). Such a substitution results in stabilized ferromagnetism. Fe substitution introduces variation in coercivity as an intrinsic magnetic property in Fe-doped CuO, and not as a secondary impurity phase.

Synthesis, Morphology, Optical and Electrical Properties of Cu(1−x) Fe(x) O Nanopowder.

The pure and Fe-doped CuO nanoparticles of the series Cu(1−x) Fe(x)O (x = 0, 0.027, 0.055, 0.097 and 0.125) were synthesized by a simple low temperature sol­gel method. Synthesized samples were characterized by a series of techniques including Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray electron spectroscopy (EDX), Diffuse Reflectance Spectroscopy (DRS), Fourier Transform Infrared Spectroscopy (FTIR), Hall Effect Set-up and Current­Voltage (I­V) characteristics. FESEM analysis shows formation of disc type structure increasing in grain size with Fe concentration in CuO. EDX confirmed the incorporation of iron in CuO. FTIR results of pure and Fe doped CuO samples have confirmed the formation of monoclinic CuO. The optical band gap estimated using Diffuse Reflectance Spectroscopy (DRS) shows the increment in the band gap values with Fe substitution. The Hall measurements show predominantly p-type conduction in all the samples and carrier densities decrease with increased Fe substitution. I­V characteristics of pure and Fe doped CuO nanoparticles show rectification behaviour of Schottky diodes.

Structural Distortion and Bandgap Increment in Nanocrystalline Wurtzite Si Substituted ZnO.

Crystalline Zn(1−x) Si(x) O(0 ≤ x ≤ 0.156) nanoparticles reveal decreasing particle size with increasing Si content and a undistorted wurtzite form until x = 0.062 beyond which local deformation is observed maintaining the parent structure. There is a sharp increment in bandgap with nominal Si-doping and then almost saturates onwards. Moreover thermal annealing demonstrate the increase bandgap and decreasing lattice parameters. The details of samples synthesis and characterization is presented in the present manuscript.

Synthesis of Ammonia-Assisted Porous Nickel Ferrite (NiFe2O4) Nanostructures as an Electrode Material for Supercapacitors.

In this work, we report a low cost, facile synthesis method for Nickel ferrite (NiFe2O4) nanostructures obtained by chemical bath deposition method for alternate transition metal oxide electrode material as a solution for clean energy. We developed a template free ammonia assisted method for obtaining porous structure which offering better supercapacitive performance of NiFe2O4 electrode material than previously reported for pure NiFe2O4. Here we explore the physical characterizations X-ray diffraction, FESEM, HRTEM performed to under-stand its crystal structure and morphology as well as the electrochemical measurements was performed to understand the electrochemical behaviour of the material. Here ammonia plays an important role in governing the structure/morphology of the material and enhances the electrochemical performance. The specific capacitance of 541 Fg⁻¹ is achieved at 2 mVs⁻¹ scan rate which is highest for the pure NiFe2O4 electrode material without using any addition of carbon based material, heterostructure or template based method.

Sharp Raman anomalies and broken adiabaticity at a pressure induced transition from band to topological insulator in Sb2Se3.

The nontrivial electronic topology of a topological insulator is thus far known to display signatures in a robust metallic state at the surface. Here, we establish vibrational anomalies in Raman spectra of the bulk that signify changes in electronic topology: an E(g)(2) phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb(2)Se(3) crystal. Our first-principles calculations confirm the electronic transition from band to topological insulating state with reversal of parity of electronic bands passing through a metallic state at the ETT, but do not capture the phonon anomalies which involve breakdown of adiabatic approximation due to strongly coupled dynamics of phonons and electrons. Treating this within a four-band model of topological insulators, we elucidate how nonadiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator.