Crystal Engineering最新文献

The present paper is focused on structural, microstructural and compositional studies on nanophasic LaCoO₃ thin films obtained by the sol-gel route. The sample structure and microstructure were investigated by Glancing Incidence X-Ray Diffraction (GIXRD) and X-Ray microdiffraction (MicroXRD), whereas the surface and in-depth chemical composition was studied by X-Ray Photoelectron Spectroscopy (XPS). All the films are structurally homogeneous and not textured. A cubic-to-rhomboedral phase transition was detected after the thermal treatment at 800 °C. Evidence of residual stress was found by GIXRD patterns collected at different incidence angles. After thermal annealing at 1000 °C, only the crystalline La₂O₃ phase was detected.

By means of orientation imaging microscopy, we have investigated grain orientation distributions of various BaTiO₃ ceramic samples prepared using different preparation routes. We present details of the required surface preparation steps in order to enable an automated orientation mapping. The samples are characterized by image quality (IQ), grain size (GS) and grain orientation (IPF) maps. Finally, the grain orientation distribution functions are obtained from the measured data. It is shown that the samples do not exhibit any preferred grain orientations.

The electrocrystallization processes of Zn–Ni coatings from weakly acid sulfate solutions with the addition of citrate and acetate complexing compounds have been compared. The deposition kinetics and the influence of electrolyte composition on the Zn–Ni alloy composition and on some physicochemical properties (corrosion resistance, texture, phase composition, morphology) were determined. It was found that the properties of coatings obtained under the same operating conditions in electrolytes with the same [Ni(II)]/[Zn(II)] concentration ratio and pH but containing different complexing agents were different. The composition of the deposits and their texture as well as phase structure were found to depend on the complexing species present. Coatings deposited from acetate solutions are richer in Ni than those from citrate solutions. The corrosion resistance of a Zn–Ni alloy depends in practice on the percentage of Ni, but in sulfate–citrate electrolytes, layers containing less Ni were obtained with the same corrosion resistance as Ni-rich coatings deposited from acetate solution. The corrosion current decreases more rapidly with increasing Ni content. This effect is connected mainly with phase composition. In citrate solutions practically single-phase (hexagonal η) deposits were obtained which provide better protection with a lower corrosion rate in comparison with alloys consisting of three phases (hexagonal η, monoclinic δ, regular γ) deposited from acetate baths.

TlBa₂Ca₂Cu₃O₉ (Tl-1223) superconducting thick films with J_c as high as 0.8 MA/cm² have been recently prepared in a two step process which involves (i) the deposition of the “Ba₂Ca₂Cu₃O₇” precursor on heated LaAlO₃ substrates by spray pyrolysis and (ii) an ex-situ thallination treatment, following a procedure already applied for bulk samples. The kinetics for the formation of the superconducting phase has been studied to determine the optimum processing temperature and time for better control of the grain growth and the superconducting properties. The data analysis, based on a diffusion model, leads to an estimated value for the activation energy E_a of 161 kJ/mol. The effect of fluorine addition on the film morphology and microstructure is also studied. It is found that both c-axis orientation (Δω = 0.34°) and in-plane texture (Δϕ =0.43°) are significantly improved with respect to F-free films.

The complex ternary system Ba-Cu- O has been re-visited in 0.1 MPa oxygen pressure. It is established that for such pressure, the $\text{BaO}{}_{\mathrm{<mtext>2</mtext>}}\text{=}\text{BaO+}\text{1}\text{2}\text{O}{}_2$ reaction has an important role for reaching the equilibrium state. The pathway for the phase formation is then described in ternary sections BaO₂-BaO-CuO. We have specified the temperatures and the forming reactions of the 3 compounds in the system: Ba₂CuO_3.04 decomposes by peritectic-like reaction at 1033°C and shows a structural transition from orthorhombic to tetragonal for at 825°C, BaCuO₂ is a congruent melting compound at 1035°C and Ba₂Cu₃O_5.5 undergoes a peritectoïdic decomposition into BaCuO₂ and CuO at 893°C.

The ordering of A and B atoms of compounds A_xB_y on the different positions of a lattice is analyzed by the numbers T₁ T₂ T₃; r of nearest, next-nearest and third neighbors of the same kind and the ratio r=y/x. The T₁, T₂ or T₁, T₂, T₃ structure maps containing all possible structures select the structures with maximum attractive or repulsive interactions which are stabilized by enthalpy. These structures at the borders of the structure maps are assembled from different structural units with different physical properties. The square net, body-centered cubic and diamond lattices containing surface structures, ordered alloys or semiconducting adamantanes are closely related. A periodic variation of crystal structures and interactions is suggested for the low-temperature modifications of the elements.

The synthesis and structural characterization of one-dimensional coordination/H-bonded polymers M(18-crown-6) [H{ONC(CN)C(O)C₆H₅}₂] (M=NH₄, Tl) is reported. The hydrogen oximate anion is formed by means of strong hydrogen bonding O-H-O between two nitroso groups, it possesses a centrosymmetric structure and bridges two macrocyclic fragments. In both the structures these fragments M(18-crown-6) adopt unusual geometry with the large cations being situated exactly in the center of the crown ether cavity.

The solid-state packing arrays of nine 4-phenyl substituted 2-amino-1,3-thiazoles have been examined and their hydrogen-bonding networks discussed. The nine compounds, in addition to 2-amino-1,3-thiazole 1, were 2-amino-4-phenyl-1,3-thiazole 2, 2-amino-4-phenyl-1,3-thiazolium bromide monohydrate 3, ethyl 2-amino-4-phenyl-1,3-thiazole-5-carboxylate 4, 2-amino-4-(3-coumarin)-1,3-thiazole 5, 2-amino-4-(4-methylphenyl)-1,3-thiazole 6, 2-amino-4-(2-hydroxyphenyl)-1,3-thiazole 7, 2-amino-4-(4-bisphenyl)-1,3-thiazole 8, 2-amino-4-(1-naphthyl)-1,3-thiazole 9, and 2-amino-4-(2-naphthyl)-1,3-thiazolium bromide 10. The single-crystal x-ray structures of 1–5 have been previously reported while the structures of 6–10 are presented in this paper. A variety of different packing motifs are observed with only four (4, 5, 6 and 9) exhibiting the characteristic R₂²(8) hydrogen-bonded 2-amino-1,3-thiazole dimers. In two of these four structures (6 and 9) potential N–H⋯π hydrogen-bonding interactions exist whereas all remaining structures exhibit a combination of N–H⋯N with either N–H⋯O, N–H⋯S or N–H⋯Br associations in their hydrogen-bonding networks.