Strain-driven autonomous control of cation distribution for artificial ferroelectrics

In past few decades, there have been substantial advances in theoretical material design and experimental synthesis, which play a key role in the steep ascent of developing functional materials with unprecedented properties useful for next-generation technologies. However, the ultimate goal of synthesis science, i.e., how to locate atoms in a specific position of matter, has not been achieved. Here, we demonstrate a unique way to inject elements in a specific crystallographic position in a composite material by strain engineering. While the use of strain so far has been limited for only mechanical deformation of structures or creation of elemental defects, we show another powerful way of using strain to autonomously control the atomic position for the synthesis of new materials and structures. We believe that our synthesis methodology can be applied to wide ranges of systems, thereby providing a new route to functional materials.

SYNTHESIS AND LUMINESCENCE PROPERTIES OF K0,5xBi1-0,5x(MoxV1-x)O4 SOLID SOLUTIONS

The conditions of heterovalent substitution in cationic and anionic positions of хK0,5Bi0,5MoO4 – (1-х)BiVO4 system within range of х = 0.1-0.9 with forming of К0,5xBi1-0,5x(MoxV1-x)O4 solid solutions, those possess scheelite-like type structure have been studied. All the samples of series were obtained by solid state technique. It was shown by IR spectroscopy and X-ray diffraction studies that molybdenum and vanadium occupying one crystallographic position with statistical distribution in х = 0.1–0.9 range of substitution. As result a lowering of lattice symmetry from tetragonal to monoclinic take place with increasing of molybdenum content. Charge compensation in system is realized through proportional substitution of bismuth by potassium in (К/Bi)O8 polyhedra. The data on diffuse reflectance indicate that increasing of substitution degree, x, lead to proportional increasing of band gap values from 2.33 to 2.72 eV for the semiconductors obtained. Intrinsic photoluminescence of the samples has been observed at low temperatures but is absent at room temperature. Total intensity of visible luminescence increases with increasing of molybdenum content in К0.5xBi1-0.5x(MoxV1-x)O4 solid solutions. Spectra of photoluminescence consist of wide two-component band with maxima at 620 and 705 nm, respectively. Simultaneous analysis of literature data and dependences of luminescence intensity on molybdenum content allow assumption that short-wavelength component related with centers, those formed on molybdate groups. Long-wavelength component related with vanadate groups. The wide bands at 375 and 410 nm in the photoluminescence excitation spectra were ascribed to absorption transitions in molybdate and vanadate oxyanions, respectively. The solid solutions studied can be used as hosts for luminescent ions or in elaboration of photocatalysts.

Димерная самоорганизация примесных ионов эрбия в синтетическом форстерите

The electron paramagnetic resonance spectra of impurity trivalent erbium ions in synthetic forsterite single crystals (Mg_2SiO_4) have been studied by the electron paramagnetic resonance method in the X and Q frequency bands. It is found that erbium ions predominantly substitute for magnesium ions in crystallographic position M1 that is characterized by the inversion symmetry of the crystal field. In this case, a pronounced effect of dimer self-organization of erbium ions during the crystal growth takes place; the effect is manifested in the fact that the concentration of erbium dimer associates consisting of two closely spaced ions bound by the spin– spin interaction is several orders of magnitude higher than the concentration of dimer associates that form randomly at a statistical distribution of impurity ions in the forsterite crystal lattice. The directions of the main magnetic axes and the parameters of the effective spin Hamiltonian describing the magnetic characteristics of impurity erbium centers have been determined.

Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member

A compilation of Fe3+-bearing chlorite analyses is used: (1) to investigate the Alfree di-trioctahedral (AFDT) substitution 2Fe3++□= 3(Mg,Fe2+) in chlorite; and (2) to estimate the composition of a ferri-sudoite end-member (Si3Al)[(Fe2+,Mg)2□Al]O10(OH)8within the chlorite solid-solution domain. According to our observations, up to two Fe3+cations might be allocated in the M2-M3 chlorite sites by the substitution AFDT, which does not involve Al. These unexpected observations were made possible by the development of μXANES techniques allowingin situmeasurements ofXFe3+(Fe3+/(Fe2++ Fe3+)) in heterogeneous chlorite. Although further studies are required to confirm the crystallographic position of Fe3+ and refine its ionic/ magnetic behaviour in chlorite, this development creates opportunities for developing new geothermometers.

MANIPULATING ATOMS ONE BY ONE WITH A SCANNING TUNNELING MICROSCOPE

By using an STM operated in ultrahigh vacuum, we can extract single Si atoms from any predetermined positions of the Si(111)-(7×7) surface through field evaporation. This technique enables us to create novel atomic-scale structures, and even to fabricate a single atom groove and chain on the surface. The extracted Si atoms can be redeposited onto the surface, although the crystallographic position of these deposited Si atoms changes as their density increases. We have demonstrated that natural Si vacancy defects existing on the surface can be repaired by this technique. The deposited Si atoms can be reremoved by picking them up again with the tip, the substrate atomic arrangement remaining unperturbed. We can also remove individual hydrogen atoms from hydrogen-passivated Si(100)-(2×1) surfaces. A chain with equal separation of Si dimers produced by hydrogen desorption has been created. These results demonstrate the potential of STM for the construction of electronic devices with atomic dimensions.

Bis((S)-5,5-dimethylthiazolidine-4-carboxylic acid) protium chloride hydrate [(C6H11NO2S)2H]Cl•H2O, a salt containing a hemi-protonated zwitterion

The X-ray crystal structure of bis((S)-5,5-dimethylthiazolidine-4-carboxylic acid) protium chloride hydrate, I, has been determined. Crystals are orthorhombic, P212121, with cell dimensions a = 6.463(2), b = 11.832(3), c = 23.966(6) Å, and Z = 4. The structure was solved by standard methods and refined to R = 0.073, Rw = 0.064 for 2969 independent reflections. Compound I is composed of two zwitterion molecules bridged through a proton which causes a very short hydrogen bond, O … O′ = 2.450 Å. The proton is located roughly halfway between the two carboxylate oxygen atoms, but is not on a special crystallographic position. Characteristic features of the infrared and Raman spectra, mass spectra, and 1H and 13C nmr spectra are discussed.