Symmetry Analysis of Magnetoelectric Effects in Perovskite-Based Multiferroics

In this article, we performed symmetry analysis of perovskite-based multiferroics: bismuth ferrite (BiFeO3)-like, orthochromites (RCrO3), and Ruddlesden–Popper perovskites (Ca3Mn2O7-like), being the typical representatives of multiferroics of the trigonal, orthorhombic, and tetragonal crystal families, and we explored the effect of crystallographic distortions on magnetoelectric properties. We determined the principal order parameters for each of the considered structures and obtained their invariant combinations consistent with the particular symmetry. This approach allowed us to analyze the features of the magnetoelectric effect observed during structural phase transitions in BixR1−xFeO3 compounds and to show that the rare-earth sublattice has an impact on the linear magnetoelectric effect allowed by the symmetry of the new structure. It was shown that the magnetoelectric properties of orthochromites are attributed to the couplings between the magnetic and electric dipole moments arising near Cr3+ ions due to distortions linked with rotations and deformations of the CrO6 octahedra. For the first time, such a symmetry consideration was implemented in the analysis of the Ruddlesden–Popper structures, which demonstrates the possibility of realizing the magnetoelectric effect in the Ruddlesden–Popper phases containing magnetically active cations, and allows the estimation of the conditions required for its optimization.

Синтез и оптические свойства кристаллов метабората меди, легированного никелем

This work presents information on the growth and spectroscopic study of single crystals of copper metaborate doped with nickel Cu1-xNixB2O4 (x = 0.05, 0.1). In the absorption spectra of both crystals, satellites related to Cu centers distorted by impurity Ni atoms were observed near the lines of zero phonon transitions. Polarization studies in the isotropic ab-plane of the tetragonal crystal Cu1-xNixB2O4 show the presence of linear magnetic dichroism in the magnetically ordered state, which was previously observed both in manganese-doped and undoped copper metaborates CuB2O4. The temperature of magnetic phase transitions into the collinear antiferromagnetic and into helicoidal structures, TN = 19.1 K and T* = 8.6 К, respectively, were determined from the temperature dependence of the dichroic signal.

New Multicolor Tungstate-Molybdate Microphosphors as an Alternative to LED Components

Due to the ongoing need to create phosphors with the appropriate emission color for the production of light emitting diodes, we decided to synthesize a series of multicolour microphosphors with tunable visible emissions, depending on the composition of dopant ions. In this work, we investigated the structure, morphology, and luminescent properties of new molybdate–tungstate phosphors co-doped with Tb3+ and Eu3+ ions. The conventional high temperature solid state method was used to prepare a series of CaMoyW1−yO4:Eu3+x/Tb3+1−x materials. In order to obtain phosphors with the most promising luminescent properties, the experiment was planned by taking into account the different composition of the matrix and the concentration of the particular dopant ions (Eu3+x/Tb3+1−x, x = 0.001, 0.003, 0.005, 0.007, 0.009). As a result, luminescent materials were obtained with a pure tetragonal crystal structure, the space group of I41/a, confirmed by X-ray diffraction (XRD). The size and shape of the particles obtained from the materials were analyzed based on scanning electron microscopy images. Luminescence spectroscopy (excitation and emission spectra, decay lifetimes) was utilized to characterize the luminescence properties of the as-prepared phosphors. The color change of the emission from green-yellow to orange-red was confirmed using the 1931 Comission Internationale de l’Eclairage (CIE) chromaticity coordinates and color correlated temperature (CCT).

First principles calculations on the novel high pressure phase of HfC

A new high-pressure structure of hafnium monocarbide (HfC) has been predicted by particle swarm optimization (PSO) algorithm based on first principles calculations. The newly found phase AuCu (L1[Formula: see text] belongs to the tetragonal P4/mmm space group. The transition pressure of NaCl (B1)[Formula: see text]L10 is predicted to be 387.6 GPa, which is much lower than that of B1[Formula: see text]CsCl (B2). L10 phase is found to transform to B2 structure at [Formula: see text]896.7 GPa. The structural stability criterion for tetragonal crystal was successfully deduced, which confirms the mechanical stability of L10 phase according to the calculated elastic constants. Thus, the equilibrium structure of HfC under high pressure was predicted to be L10 phase instead of B2. Furthermore, the bulk modulus, shear modulus, Young’s modulus and the compressional and shear wave velocities of HfC in B1 and L10 phases are found to increase monotonically as the pressure increases.

Synthesis, Crystal Structure, Hirshfeld Surface, Energy Framework and Molecular Docking of 2-(((6-Methoxy pyridin-3-yl)imino)methyl)Phenol

The structure of 2-(((6-methoxypyridin-3-yl)imino)methyl)phenol (MPIMP) (C13H12N2O2) has been determined by X-ray diffraction methods. It crystallizes in the tetragonal crystal system with space group P42/n and unit cell dimensions a = 14.2958(3) Å, b = 14.2958(3) Å, c = 11.0179(3) Å, V = 2251.73(12) Å3, Z = 8. The structure has been refined by full-matrix least square procedure to a final R-value of 0.0518(wR2= 0.1312) for 1709 observed reflections. The molecules linked via two intermolecular (C-H...N and C-H...O) hydrogen bonds. The crystal structure was further stabilized by a strong intramolecular N-H...O hydrogen bond. The Hirshfeld surface analysis reveals the interaction contacts of the molecule and the strength of molecular packing in the crystal. The energy framework has been performed through different intermolecular interaction energies for structural stability. The molecular docking of MPIMP was performed against tuberculosis enzyme Decaprenyl-phosphoryl-b-Dribose 20-epimerase (DprE1, PDB code: 4KW5) to reconnoiter the binding interactions at the active sites.

Drastic improvement of Curie temperature by chemical pressure in N-type diluted magnetic semiconductor Ba(Zn,Co)$$_{2}$$As$$_{2}$$

We report the effect of chemical pressure on the ferromagnetic ordering of the recently reported n-type diluted magnetic semiconductor Ba(Zn$$_{1-x}$$ 1 - x Co$$_{x}$$ x )$$_{2}$$ 2 As$$_{2}$$ 2 which has a maximum $$T_C$$ T C $$\sim$$ ∼ 45 K. Doping Sb into As-site and Sr into Ba-site induces negative and positive chemical pressure, respectively. While conserving the tetragonal crystal structure and n-type carriers, the unit cell volume shrink by $$\sim$$ ∼ 0.3$$\%$$ % with 15$$\%$$ % Sr doping, but drastically increase the ferromagnetic transition temperature by 18$$\%$$ % to 53 K. Our experiment unequivocally demonstrate that the parameters of Zn(Co)As$$_{4}$$ 4 tetrahedra play a vital role in the formation of ferromagnetic ordering in the Ba(Zn,Co)$$_{2}$$ 2 As$$_{2}$$ 2 DMS.

The Isoelectric Point and the Surface Charge of Barium Titanate Nanoparticles/Graphene Oxide Determined Using the Electrophoretic Mobility Technique

Barium titanate nanopowders, and composite materials of barium titanate/ graphene oxide (10 wt.% of graphene oxide according to the initial composite composition) were synthesized by hydrothermal method at the fixed reaction condition of 200 oC and 24 hours. The obtained powders were characterized by different techniques: X-ray diffraction, FTIR spectroscopy, Particles size distribution, and Scanning electron microscopy. Zeta potential measurement under electrophoretic mobility technique was also employed to investigate the stability of the BaTiO3 nanoparticles and composite materials of barium titanate/graphene oxide. The results showed that the BaTiO3 present with the tetragonal crystal structure (P4mm, a = 4.0000 Å, c = 4.0109 Å) and has uniform morphology with the grain sizes are in the range of 70 - 140 nm. The BaTiO3 nanoparticles were well distribution and covered on a surface of graphene oxide. The BaTiO3 nanoparticles, and BaTiO3/graphene oxide are stable in alkali, neutral media, and acidic media up to pH ~ 5.

Synthesis of 2D-CZTS Nanoplate as Photocathode Material for Efficient PEC Water Splitting

Fabrication of economically viable photocathode for hydrogen energy production through solar water splitting is a major research among the scientific community for a decade. P-type compound Cu2ZnSnS4 (CZTS) is very interesting material due to its absorption property, earth-abundant constituents and environmental friendliness that serves as a suitable candidate to act as a photocathode. In the present work, Cu2ZnSnS4 (CZTS) nanoparticles are synthesized by simple one-step chemical method and annealed at 350 °C for three different times (60 minutes, 90 minutes and 120 minutes). The effect of annealing time on the structural, optical and photoelectrochemical properties are investigated. XRD pattern indicates the formation of tetragonal crystal structure and the crystallinity increases according to the annealing time. 2-D nanoplate morphology is obtained for the sample that was annealed for 120 minutes. From the absorption spectra, it was found that the band gap decreases with increase of annealing time. Further, the prepared nanoparticle thin films are used as a cathode for photoelectrochemical water splitting application. Among these, the nanoparticles that are annealed for 120 minutes showed higher photocurrent density when compared to nanoparticles annealed for 60 minutes and 90 minutes.

Coherent crystal branches: the impact of tetragonal symmetry on the 2D confined polymer nanostructure

The symmetry of polymer crystals greatly affects the optical, thermal conductivity and mechanical properties of the materials. Past studies have shown that the two-dimensional (2D) confined crystallization of polymer nanorods could produce anisotropic structures. However, few researchers have focused on understanding confined nanostructures from the perspective of crystal symmetry. In this research, we demonstrate the molecular chain self-assembly of tetragonal crystals under cylindrical confinement. We specifically selected poly(4-methyl-1-pentene) (P4MP1) with a 41 or 72 helical conformation (usually crystallizing with a tetragonal lattice) as the model polymer. We found a coherent crystal branching of the tetragonal crystal in the P4MP1 nanorods. The unusual 45°- and 135°-{200} diffractions and the meridional 220 diffraction (from 45°-tilted crystals) have shown a uniform crystal branching between the a 1-axis crystals and the 45°-tilted crystals in the rod long axis, which originates from a structural defect associated with tetragonal symmetry. Surprisingly, this chain packing defect in the tetragonal cell can be controlled to develop along the rod long axis in 2D confinement.