Synthesis of 2,4,6-Trisubstituted Pyrimidines through Copper-Catalyzed [4 + 2] Annulation of α,β-Unsaturated Ketoximes with Activated Nitriles

The copper-catalyzed [4 + 2] annulation of α,β-unsaturated ketoximes with activated nitriles for the rapid construction of 2,4,6-trisubstituted pyrimidines in moderate to good yields has been developed. The reaction features synthetic simplicity, good functional group tolerance, and gram-scale applicability. A plausible mechanism is proposed based on mechanistic investigations

Crystal Chemistry and Magnetic Properties of Gd-Substituted Aurivillius-Type Bi₅FeTi₃O₁₅ Ceramics

Aurivillius-phase ferroelectrics can be turned into multiferroic materials by incorporating magnetic ions. The four-layer Aurivillius-type system Bi₅FeTi₃O₁₅ is well-known to show a strong magnetoelectric effect; however, much controversy exists on its magnetic state and the possible multiferroicity at room temperature. In this paper, we report a detailed investigation on the interconnections between crystal chemistry and magnetic properties of Bi₅FeTi₃O₁₅ ceramics chemically modified by the A-site gadolinium substitution. The structural studies showed that all Bi_5–<i>x</i>Gd_<i>x</i>FeTi₃O₁₅ (0 ≤ <i>x</i> ≤ 1) samples adopt the polar orthorhombic space group symmetry <i>A</i>2₁<i>am</i> at room temperature. The unit cell volume and the orthorhombic distortion decrease alongside the reduction of octahedral tilts by increasing the amount of Gd added. The decrease in tilting distortion of the [Ti/Fe]­O₆ octahedra was further evidenced by the suppression of the Raman A₁[111] tilt mode at 233 cm^–1. By using superconducting quantum interference and vibrating sample magnetometry, it was demonstrated that all the ceramics are paramagnetic from 5 K up to 700 K. It was thus concluded that the A-site substitution of Bi₅FeTi₃O₁₅ with magnetic Gd ions brings about a slight structural relaxation of the parental orthorhombic lattice, but it is not an effective way to induce multiferroic properties in the Aurivillius compound. We suggest that the room-temperature (ferri/ferro/antiferro-) magnetism in Bi₅FeTi₃O₁₅ previously reported in the literature might be due to the presence of magnetic impurities or local short-range magnetic ordering formed during material processing under different conditions

Relaxor ferroelectric and photocatalytic properties of BaBi4Ti4O15

Aurivillius phase BaBi4Ti4O15 micro-sized powders were produced by solid-state reaction and their photocatalytic properties were reported for the first time. X-ray diffraction revealed the polar orthorhombic structure. BaBi4Ti4O15 ceramics exhibited diffuse phase transition at ~ 410 C. The freezing temperature of 274 C was obtained by fitting the Vogel-Fulcher law. The distinct ferroelectric domain switching current peaks in current - electric field (I-E) loop and piezoelectric coefficient d33 value of 7.0  0.1 pC/N at room temperature further demonstrated relaxor ferroelectric behavior of BaBi4Ti4O15. UV-vis absorption spectra indicated that BaBi4Ti4O15 had a direct band gap of 3.2 eV. The photocatalytic study showed 15 % degradation of Rhodamine B (RhB) solution by BaBi4Ti4O15 powders after 3.5 h UV-vis irradiation. The RhB degradation rate was further enhanced by depositing Ag nanoparticles on the BaBi4Ti4O15 powders surface. This work suggested that the relaxor ferroelectric BaBi4Ti4O15 is promising for photocatalytic applications

Relaxor ferroelectric and photocatalytic properties of BaBi4Ti4O15

Aurivillius phase BaBi4Ti4O15 micro-sized powders were produced by solid-state reaction and their photocatalytic properties were reported for the first time. X-ray diffraction revealed the polar orthorhombic structure. BaBi4Ti4O15 ceramics exhibited diffuse phase transition at ~ 410 C. The freezing temperature of 274 C was obtained by fitting the Vogel-Fulcher law. The distinct ferroelectric domain switching current peaks in current - electric field (I-E) loop and piezoelectric coefficient d33 value of 7.0 0.1 pC/N at room temperature further demonstrated relaxor ferroelectric behavior of BaBi4Ti4O15. UV-vis absorption spectra indicated that BaBi4Ti4O15 had a direct band gap of 3.2 eV. The photocatalytic study showed 15 % degradation of Rhodamine B (RhB) solution by BaBi4Ti4O15 powders after 3.5 h UV-vis irradiation. The RhB degradation rate was further enhanced by depositing Ag nanoparticles on the BaBi4Ti4O15 powders surface. This work suggested that the relaxor ferroelectric BaBi4Ti4O15 is promising for photocatalytic applications

Relaxor behavior and photocatalytic properties of BaBi2Nb2O9

Lead‐free Aurivillius phase BaBi2Nb2O9 powders were prepared by solid‐state reaction. Ferroelectric measurements on BaBi2Nb2O9 (BBNO) ceramics at room temperature provided supporting evidence for the existence of polar nanoregions (PNRs) and their reversible response to an external electric field, indicating relaxor behavior. The photocatalytic degradation of Rhodamine B reached 12% after 3 hours irradiation of BBNO powders under simulated solar light. Silver (Ag) nanoparticles were photochemically deposited onto the surface of the BBNO powders and found to act as electron traps, facilitating the separation of photoexcited charge carriers; thus, the photocatalytic performance was significantly improved. The present study is the first examination of the photochemical reactivity of a relaxor ferroelectric within the Aurivillius family with PNRs

Copper-Catalyzed Three-Component Cascade Annulation for Divergent Syntheses of Imidazoles and Dihydroimidazoles

The first example of divergent N-heterocycle syntheses through a copper-catalyzed three-component reaction of α,β-unsaturated ketoximes, paraformaldehyde, and amines has been documented. In particular, this divergent synthetic strategy was achieved by controlling the reaction conditions to afford the corresponding imidazoles and dihydroimidazoles in moderate to good yields with a broad substrate scope and good functional group compatibility

Terahertz Faraday Rotation of SrFe₁₂O₁₉ Hexaferrites Enhanced by Nb Doping

The magneto-optical and dielectric behavior of M-type hexaferrites as permanent magnets in the THz band is essential for potential applications like microwave absorbers and antennas, while are rarely reported in recent years. In this work, single-phase SrFe12–xNbxO19 hexaferrite ceramics were prepared by the conventional solid-state sintering method. Temperature dependence of dielectric parameters was investigated here to determine the relationship between dielectric response and magnetic phase transition. The saturated magnetization increases by nearly 12%, while the coercive field decreases by 30% in the x = 0.03 composition compared to that of the x = 0.00 sample. Besides, the Nb substitution improves the magneto-optical behavior in the THz band by comparing the Faraday rotation parameter from 0.75 (x = 0.00) to 1.30 (x = 0.03). The changes in the magnetic properties are explained by a composition-driven increase of the net magnetic moment and enhanced ferromagnetic exchange coupling. The substitution of the donor dopant Nb on the Fe site is a feasible way to obtain multifunctional M-type hexaferrites as preferred candidates for permanent magnets, sensors, and other electronic devices