Nanostructural crystallization of metals

Based on thermodynamic calculations, it is shown that metal crystallization is an equilibrium nanostructural process. At the beginning, trigonal or tetragonal structure-forming nanocrystals are formed from elementary nanocrystals. Then crystallization centers are formed from them. Further, tetragonal or hexagonal dendrites are formed from them and tetragonal or trigonal structure-forming nanocrystals. Their forms depend on the degree of branching of dendrites. The most branched of them (compact dendrites) are tetragonal or hexagonal crystals.

Dispersion Diagram of Trigonal Piezoelectric Phononic Structures with Langasite Inclusions

The dispersion relation of elastic Bloch waves in 1-3 piezoelectric phononic structures (PPnSs) with Langasite (La3Ga5SiO14) inclusions in a polymeric matrix is reported. Langasite presents promising material properties, for instance good temperature behaviour, high piezoelectric coupling, low acoustic loss and high quality factor. Furthermore, Langasite belongs to the point group 32 and has a trigonal structure. Thus, the 2-D bulk wave propagation in periodic systems with Langasite inclusions cannot be decoupled into XY and Z modes. The improved plane wave expansion (IPWE) is used to obtain the dispersion diagram of the bulk Bloch waves in 1-3 PPnSs considering the classical elasticity theory and D3 symmetry. Full band gaps are obtained for a broad range of frequency. The piezoelectricity enhances significantly the band gap widths and opens up a narrow band gap in lower frequencies for a filling fraction of 0.5. This study should be useful for surface acoustic wave (SAW) filter and 1-3 piezocomposite transducer design using PPnSs with Langasite.

New Series of Ternary Metal Chloride Superionic Conductors for High Performance All-Solid-State Lithium Batteries

Understanding the relationship between structure, ionic conductivity, and synthesis is the key to the development of solid electrolytes for all-solid-state Lithium batteries. Here, we investigate chloride solid electrolytes with compositions Li3 − 3xM1+xCl6 (-0.14 < x ≤ 0.5, M = Tb, Dy, Ho, Y, Er, Tm). When x > 0.04, a trigonal to orthorhombic phase transition occurs in the isostructural Li-Dy-Cl, Li-Ho-Cl, Li-Y-Cl, Li-Er-Cl and Li-Tm-Cl solid electrolytes. The new orthorhombic phase shows a four-fold increase in ionic conductivity up to 1.3×10− 3 S cm− 1 at room temperature for Li2.73Ho1.09Cl6 (x = 0.09) when compared to the trigonal Li3HoCl6. For isostructural Li-Dy-Cl, Li-Y-Cl, Li-Er-Cl and Li-Tm-Cl solid electrolytes, about one order of magnitude increase in ionic conductivities are observed for the orthorhombic structure compared to the trigonal structure. Using the Li-Ho-Cl components as an example, detailed studies of its structure, phase transition, ionic conductivity, air stability and electrochemical stability have been made. Molecular dynamics simulations based on density functional theory reveal that the different cations arrangement in the orthorhombic structure leads to a higher lithium diffusivity as compared to the trigonal structure, rationalizing the improved ionic conductivities of the new Li-M-Cl electrolytes. All-solid-state batteries of In/Li2.73Ho1.09Cl6/NMC811 demonstrate excellent electrochemical performance at both room temperature and − 10°C. As relevant to the vast number of isostructural halide electrolytes, the present structure control strategy provides guidance for the design of novel halide superionic conductors.

First-principles Investigation of Structure and Electronic Properties of NiTe2 Fermi Crossing Type-II Dirac Semimetal

The electronic structure aspect of transition metal dichalcogenides (TMDs) has so far received intensive research interest. NiTe2 is a noble candidate for type-II DSM with Dirac point near the Fermi surface. In this paper we present a systematic investigation of the structural stabilities and electronic properties of NiTe2 using density functional theory via a plane wave pseudopotential method in the context of the Perdew–Burke–Ernzerh of generalized gradient approximation. The structural parameters, partial and total density of states (DOS) were systematically studied. Our structural study indicates that the material has a trigonal structure with P3̅m1 space group. In addition, we have computed the cohesive energy and the DOS at the Fermi level [N(Ef)]. The results show that NiTe2 is stable.

Different Structural Evolutions of inorganic perovskite CsGeI3

Distinguished from CsSnI3 perovskite systems, the most stable non-centrosymmetric trigonal structure (space group of R3m) of CsGeI3 perovskite system is found in our calculations. We systematically study the differences between...

Applications of Smart Material of Li2O-(Nb/Ta)2O5-TiO2 Solid Solution Having a Unique Periodical Structure

In the Li2O-M2O5-TiO2 system, Li1+x-yM1-x-3yTix+4yO3 (M = Nb, or Ta, 0.06 ≤ x ≤ 0.33, 0 ≤ y ≤ 0.175 (LMT) forms a superstructure, known as smart material. The superstructure is formed by periodical insertion of a corundum-type intergrowth layer of [Ti2O3]2+ in a matrix having a trigonal structure during the grain growth. To apply this unique structure as a host material of phosphor, new phosphors doped with Mn4+ ion with a red emission colour, which had a broad peak around 685 nm excited by 493 nm. In order to improve the PL intensity, we investigated the compositions, Mn4+ ratio and crystal structure. Results showed that PL intensity was closely related to Mn4+ ratio and its crystal structure.

Characterization and Rietveld refinements of new dense ceramics Ba3−xSrxTb3−xCexO9 (x = 1 and 1.5) perovskites

Ba3−xSrxTb3−xCexO9 (x = 1 and 1.5) ceramics (BSTC) with a relative density of 93% and a grain size distribution of 0.2–3 µm were prepared by the mixed-oxides reaction route. The crystalline structures, microstructures, valence states, and electrical properties of two ceramics were analyzed using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrical measurements. Rietveld analyses of XRPD patterns show that BSTC1 is indexed as a trigonal structure with the space group R-3c, and BSTC3/2 is indexed as an orthorhombic perovskite structure with the space group Pmcn. The EPR, XPS, and electrical conductivity results confirm that Ce and Tb ions in BSTC exist as Ce4+ and mixed-valence states of Tb4+/Tb3+, respectively. At room temperature, the two BSTC ceramics exhibit a similar semiconducting behavior. The relationships between electrical conductivity and temperature/frequency are provided. The defect chemistry is discussed.