Effect of crystallization degree on optical characteristics of NB2O5 by sol–gel process

In this study, Nb2O5 was prepared by the sol–gel method. Crystallization process was investigated by thermal analysis (TG–DSC), X-ray diffraction (XRD), UV–vis spectra and Raman spectra. TG–DSC results indicated that amorphous Nb2O5 appeared at 460[Formula: see text]C. XRD results indicated that amorphous Nb2O5 transformed into pseudo-hexagonal phase and crystallization degree has an increasing trend with an increase of temperature. UV–vis and Raman spectra results reflected the significant variations of optical property and atomic structure in this process. Nb2O5 atomic arrangement transforms from short-range order to medium-range order, then to long-range order. Atoms transform into long-range ordered structure through connection of structural units with increasing temperature. Additionally, crystallization degree, optical property and atomic arrangement all are mutually connected in the crystallization process.

In Situ Observation of the Chemical Bonding State of Si in the Molten State of Eutectic Au-Si alloy of Au81Si19 by Using a Soft X-ray Emission Spectroscopy Electron Microscope

Phase diagram of Au-Si binary alloy system shows a large drop of melting temperature of about 1000 K compared with that of Si at a composition of Au:Si=81:19, where the melting temperature is about 636 K. Mixing of Au and Si below the melting temperature was observed by transmission electron microscopy experiment and found the mixed region show a diffraction pattern of a diffuse ring intensity indicating an amorphous structure of the mixed area. Si L-emission spectra, which reflects the energy state of bonding electrons of Si atom, of molten Au81Si19 alloy was measured for the first time to investigate the energy state of valence electrons of Si. The Si L-emission spectrum showed a characteristic loss of L1 peak, which is related to sp3 directional bonding in crystalline Si. The intensity profile is also different from that of molten Si reported. This suggests a characteristic atomic arrangement exist in the molten state. The intensity profile also indicated a small density of state in the molten state at Fermi energy. The obtained spectrum was compared with the calculated density of state of possible crystal structures reported. The comparison suggested that Si atoms are surrounded by 8 Au atoms in the molten state of Au81Si19 alloy. The formation of this local atomic arrangement can be an origin of a large drop of melting temperature at about Au:Si=81:19.

New Photomagnetic Ionic Salts Based on [MoIV(CN)8]4− and [WIV(CN)8]4− Anions

Three new ionic salts containing [M(CN)8]4− (M = MoIV and WIV) were prepared using large complex cations based on a non-conventional motif built with the tris(2-aminoethyl)amine (noted hereafter tren) ligand, [{M’(tren)}3(μ-tren)]6+ (M’ = CuII and ZnII). The crystal structures of the three compounds show that the atomic arrangement is formed by relatively isolated anionic and cationic entities. The three compounds were irradiated with a blue light at low temperature, and show a significant photomagnetic effect. The remarkable properties of these compounds are (i) the long-lived photomagnetic metastable states for the [Mo(CN)8]4−-based compounds well above 200 K and (ii) the rare efficient photomagnetic properties of the [W(CN)8]4−-based compound. These photomagnetic properties are compared with the singlet-triplet conversion recently reported for the K4[Mo(CN)8]·2H2O compound.

Laves phase crystal analysis (LaCA): Atomistic identification of lattice defects in C14 and C15 topologically close-packed phases

The identification of defects in crystal structures is crucial for the analysis of atomistic simulations. Many methods to characterize defects that are based on the classification of local atomic arrangement are available for simple crystalline structures. However, there is currently no method to identify both, the crystal structures and internal defects of topologically close-packed (TCP) phases such as Laves phases. We propose a new method, Laves phase crystal analysis (LaCA), to characterize the atomic arrangement in Laves crystals by interweaving existing structural analysis algorithms. The new method can identify the polytypes C14 and C15 of Laves phases, typical crystallographic defects in these phases, and common deformation mechanisms such as synchroshear and non-basal dislocations. Defects in the C36 Laves phase are detectable through deviations from the periodic arrangement of the C14 and C15 structures that make up this phase. LaCA is robust and extendable to other TCP phases. Graphic abstract

Electric field control of natural optical activity in a multiferroic helimagnet

Controlling the chiral degree of freedom in matter has long been an important issue for many fields of science. The spin-spiral order, which exhibits a strong magnetoelectric coupling, gives rise to chirality irrespective of the atomic arrangement of matter. Here, we report the resonantly enhanced natural optical activity on the electrically active magnetic excitation, that is, electromagnon, in multiferroic cupric oxide. The electric field control of the natural optical activity is demonstrated through magnetically induced chirality endowed with magnetoelectric coupling. These optical properties inherent to multiferroics may lead to optical devices based on the control of chirality.