Vibrational Properties of LaNb0.8 M0.2 O4-δ (M=As, Sb, V, and Ta).

LaNb0.8 M0.2 O4-δ (where M=As, Sb, V, and Ta) oxides with pentavalent elements of different ionic sizes were synthesized by a solid-state reaction method. The vibrational properties of these oxides have been investigated. These studies revealed that the substituent element influences both Debye temperature value as well as the Raman active vibrational modes. Additionally, the low-temperature vibrational properties of LaNb0.8 Sb0.2 O4-δ have been determined to show the phase transition occurrence at 260 K which is lower than previously reported.

Emerging oxidized and defective phases in low-dimensional CrCl3.

Two-dimensional (2D) magnets such as chromium trihalides CrX3 (X = I, Br, Cl) represent a frontier for spintronics applications and, in particular, CrCl3 has attracted research interest due its relative stability under ambient conditions without rapid degradation, as opposed to CrI3. Herein, mechanically exfoliated CrCl3 flakes are characterized at the atomic scale and the electronic structures of pristine, oxidized, and defective monolayer CrCl3 phases are investigated employing density functional theory (DFT) calculations, scanning tunneling spectroscopy (STS), core level X-ray photoemission spectroscopy (XPS), and valence band XPS and ultraviolet photoemission spectroscopy (UPS). As revealed by atomically resolved transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis, the CrCl3 flakes show spontaneous surface oxidation upon air exposure with an extrinsic long-range ordered oxidized O-CrCl3 structure and amorphous chromium oxide formation on the edges of the flakes. XPS proves that CrCl3 is thermally stable up to 200 °C having intrinsically Cl vacancy-defects whose concentration is tunable via thermal annealing up to 400 °C. DFT calculations, supported by experimental valence band analysis, indicate that pure monolayer (ML) CrCl3 is an insulator with a band gap of 2.6 eV, while the electronic structures of oxidized and Cl defective phases of ML CrCl3, extrinsically emerging in exfoliated CrCl3 flakes, show in-gap spin-polarized states and relevant modifications of the electronic band structures.

Enhancement of the Magnetic Coupling in Exfoliated CrCl3 Crystals Observed by Low-Temperature Magnetic Force Microscopy and X-ray Magnetic Circular Dichroism.

Magnetic crystals formed by 2D layers interacting by weak van der Waals forces are currently a hot research topic. When these crystals are thinned to nanometric size, they can manifest strikingly different magnetic behavior compared to the bulk form. This can be the result of, for example, quantum electronic confinement effects, the presence of defects, or pinning of the crystallographic structure in metastable phases induced by the exfoliation process. In this work, an investigation of the magnetism of micromechanically cleaved CrCl3 flakes with thickness >10 nm is performed. These flakes are characterized by superconducting quantum interference device magnetometry, surface-sensitive X-ray magnetic circular dichroism, and spatially resolved magnetic force microscopy. The results highlight an enhancement of the CrCl3 antiferromagnetic interlayer interaction that appears to be independent of the flake size when the thickness is tens of nanometers. The estimated exchange field is 9 kOe, representing an increase of ≈900% compared to the one of the bulk crystals. This effect can be attributed to the pinning of the high-temperature monoclinic structure, as recently suggested by polarized Raman spectroscopy investigations in thin (8-35 nm) CrCl3 flakes.

Modified Manganese Phosphate Conversion Coating on Low-Carbon Steel.

Conversion coatings are one of the primary types of galvanic coatings used to protect steel structures against corrosion. They are created through chemical reactions between the metal surface and the environment of the phosphating. This paper investigates the impact that the addition of new metal cations to the phosphating reaction environment has on the quality of the final coating. So far, standard phosphate coatings have contained only one primary element, such as zinc in the case of zinc coatings, or two elements, such as manganese and iron in the case of manganese coatings. The structural properties have been determined using a scanning electron microscope (SEM), X-ray diffraction (XRD), and electrochemical tests. New manganese coatings were produced through a reaction between the modified phosphating bath and the metal (Ba, Zn, Cd, Mo, Cu, Ce, Sr, and Ca). This change was noticeable in the structure of the produced manganese phosphate crystallites. A destructive effect of molybdenum and chromium was demonstrated. Microscopic analysis, XRD analysis and electrochemical tests suggest that the addition of new metal cations to the phosphating bath affects the corrosion resistance of the modified coating.

Manganese Phosphatizing Coatings: The Effects of Preparation Conditions on Surface Properties.

Manganese phosphate coating could be used to protect the surface of steel products. However, it is essential to determine the effects which process parameters, as well as the types of additives used, have on the efficiency of coating deposition. Thus, we present here a process of phosphatization of low-alloy steel (for 15 min at 95 °C) in manganese/nickel baths followed by a passivation process with the use of a silicon and zircon compounds. The microstructure and morphology of the surface were analyzed by SEM EDX and XRD methods. The obtained results showed that the manganese phosphate could be effectively formed at 95 °C in the solution containing nickel and guanidine derivatives. Anodic polarization of manganese coating was investigated in 0.5 M KCl by the analysis of polarization resistance. The effects of the activation process on corrosion properties of the coating have been examined. It was observed that an increased concentration of activating substances in the activation bath results in the enhancement of corrosion resistance.