Two conductive mechanisms in LaMnO3 thin film: Adiabatic and nonadiabatic small polaronic hopping

We have presented the structural, surface morphology, magnetic and resistivity data for perovskite LaMnO3 epitaxial thin films which are fabricated on well-oriented (001) LaAlO3 substrates by pulsed laser deposition technique. X-ray diffraction [Formula: see text]–[Formula: see text] linear scans and reciprocal space mapping measurement confirm that the out-of-plane and in-plane epitaxial relationship are LMO(001)/LAO(001) and LMO(110)/LAO(110), respectively. Surface roughness determined by atomic force microscopy was no more than 0.3 nm. In the whole studied temperature range, all films only show a paramagnetic behavior instead of any magnetic phase transitions. Correspondingly, the electron transport behaviors always exhibit an insulting state as the temperature changes from high to low. However, we find that none of theoretical models can individually be used to understand their conductive mechanisms. Further studies indicated that charge carries of high and low temperature region obey adiabatic and nonadiabatic small polaronic hopping mechanisms, respectively. This finding offers new ways of exploiting the abnormal ferromagnetism in LaMnO3 multilayer thin films.

Mechanisms of bastnasite formation: replacement of calcite by rare earth carbonates.

<div> <p>The interaction of rare earth bearing (La, Nd, Dy) aqueous solutions with calcite crystals at was studied at ambient and hydrothermal conditions (25-220 °C) and resulted in the solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of calcite by rare earth carbonates. Calcite grains were replaced from their periphery inwards, and the newly formed REE-bearing carbonates follow the crystallisation sequence lanthanite [REE<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>·8H<sub>2</sub>O] → kozoite [orthorhombic REECO<sub>3</sub>(OH)] → hydroxylbastnasite [hexagonal REECO<sub>3</sub>(OH)]. The specific rare earth involved in these processes and the temperature have a significant role in the polymorph selection, crystallisation pathways and kinetics of mineral replacement. La- and Nd-bearing kozoite, grows oriented onto the calcite surface, forming an epitaxy, due to their structural similarities. This phase forms elongated crystals on [100], with the {011} and {0-11} as major forms. The epitaxial relationship is (104) [010]<sub>cc </sub>║(001) [100]<sub>koz</sub> and is strongly dependent on the ionic radius of the rare earth in the structure of kozoite. These results have strong implications for the understanding of mineralisation reactions occurring in REE-bearing carbonatite deposits, the most important resources of rare earths in the world.</p> </div>

Two-dimensional iodine-monofluoride epitaxy on WSe2

Interhalogen compounds (IHCs) are extremely reactive molecules used for halogenation, catalyst, selective etchant, and surface modification. Most of the IHCs are unstable at room temperature especially for the iodine-monofluoride (IF) whose structure is still unknown. Here we demonstrate an unambiguous observation of two-dimensional (2D) IF bilayer grown on the surface of WSe2 by using scanning transmission electron microscopy and electron energy loss spectroscopy. The bilayer IF shows a clear hexagonal lattice and robust epitaxial relationship with the WSe2 substrate. Despite the IF is known to sublimate at −14 °C and has never found as a solid form in the ambient condition, but surprisingly it is found stabilized on a suitable substrate and the stabilized structure is supported by a density functional theory. This 2D form of IHC is actually a byproduct during a chemical vapor deposition growth of WSe2 in the presence of alkali metal halides as a growth promoter and requires immediate surface passivation to sustain. This work points out a great possibility to produce 2D structures that are unexpected to be crystallized or cannot be obtained by a simple exfoliation but can be grown only on a certain substrate.

Tracking the Emergence of Epitaxial Metal–oxide Interfaces from Precursor Alloys

Heterointerfaces with an epitaxial relationship, self-assembled nanocomposites of Pt(111)/CeO2(111) 60°, were successfully formed by simple oxidation of Pt5Ce alloy. Oxygen dissolution into the alloy causes spacial periodic compositional perturbation by...

Development of a Fluorine-Free Polymer-Assisted-Deposition Route for YBa2Cu3O7−x Superconducting Films

Polymer assisted deposition (PAD) was used as an environmentally friendly, non-fluorine, growth method for superconducting YBa2Cu3O7−x (YBCO) films. The kinetics of the thermal decomposition of the precursor powder was studied by thermogravimetry coupled with mass spectrometry (TG-QMS). YBCO films were spin coated on (100) SrTiO3 (STO) single crystalline substrates, followed by a single step thermal treatment under wet and dry O2 and O2/N2 mixture. The as-obtained films were epitaxially grown having a [001]YBCO||[001]STO out-of-plane epitaxial relationship and exhibited good superconducting properties with Tc (R = 0) > 88 K, transition widths, ΔT ≈ 2 K and critical current densities as high as 2.3 MA/cm2 at 77 K and self magnetic field.

Intermolecular channels direct crystal orientation in mineralized collagen

The mineralized collagen fibril is the basic building block of bone, and is commonly pictured as a parallel array of ultrathin carbonated hydroxyapatite (HAp) platelets distributed throughout the collagen. This orientation is often attributed to an epitaxial relationship between the HAp and collagen molecules inside 2D voids within the fibril. Although recent studies have questioned this model, the structural relationship between the collagen matrix and HAp, and the mechanisms by which collagen directs mineralization remain unclear. Here, we use XRD to reveal that the voids in the collagen are in fact cylindrical pores with diameters of ~2 nm, while electron microscopy shows that the HAp crystals in bone are only uniaxially oriented with respect to the collagen. From in vitro mineralization studies with HAp, CaCO3 and γ-FeOOH we conclude that confinement within these pores, together with the anisotropic growth of HAp, dictates the orientation of HAp crystals within the collagen fibril.

Single Source Precursor for PAD-LaMnO3 Thin Films

A new lanthanum and manganese ethylenediaminetetraacetate (EDTA) coordination polymer (EDTA4− = [(CH2N)2(CH2-COOH)(CH2COO)4]) was synthesized from La(NO3)3 and Mn(NO3)2 reagents, ethylenediaminetetraacetic acid, and water at room temperature. The structure of the new compound formed, [{La2Mn3(EDTA)3(H2O)11}·12H2O]n, was determined by the single crystal X-ray diffraction technique. The synthesis and characterization of the La(III) and Mn(II) coordination complex, characterized by FTIR spectroscopy, thermogravimetry, and differential thermal analysis of the complex, are envisaged. X-ray crystal structure determination indicates that seven- and four-coordinate modes between La(III)/Mn(Π) and H4EDTA exist. [{La2Mn3(EDTA)3(H2O)11}·12H2O]n crystallizes in the monoclinic space group C2 with unit cell parameters of a = 16.1227(17) Å, b = 14.8049(16) Å, c = 14.8736(16) Å, and β = 116.107(2)°. Using this precursor, LaMnO3 (LMO) epitaxial thin films were grown by the polymer-assisted deposition (PAD) method on (100)SrTiO3 (STO) single crystalline substrates at a temperature of 900 °C. The LMO crystallized films exhibit a (001)LMO/(001)STO out-of-plane epitaxial relationship and a smooth surface morphology.

Intermolecular Channels Direct Crystal Orientation in Mineralized Collagen

ABSTRACTThe mineralized collagen fibril is the basic building block of bone, commonly pictured as a parallel array of ultrathin carbonated hydroxyapatite (HAp) platelets distributed throughout the collagen. This orientation is often attributed to an epitaxial relationship between the HAp and collagen molecules inside 2D voids within the fibril. Although recent studies have questioned this model, the structural relationship between the collagen matrix and HAp, and the mechanisms by which collagen directs mineralization remain unclear. Here, we use XRD to reveal that the voids in the collagen are in fact cylindrical pores with diameters of ∼2 nm, while electron microscopy shows that the HAp crystals in bone are only uniaxially oriented with respect to the collagen. From in vitro mineralization studies with HAp, CaCO3 and γ-FeOOH we conclude that confinement within these pores, together with the anisotropic growth of HAp, dictates the orientation of HAp crystals within the collagen fibril.