Huili Yang

Phase transition, superstructure and physical properties of K2Fe4Se5

The structural features and physical properties of the antiferromagnetic K0.8Fe1.6Se2 (so-called K2Fe4Se5 phase) have been studied in the temperature range from 300 K up to 600 K. Resistivity measurements on both single crystal and polycrystalline samples reveal a semiconducting behavior. Structural investigations of K2Fe4Se5 by means of transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) demonstrate the presence of a well-defined superstructure within the a-b plane originating from a Fe-vacancy order along the [1−10] direction (indexed based on the supercell with space group of I4/m). Moreover, in situ heating structural analysis shows that K0.8Fe1.6Se2 undergoes a transition of the Fe-vacancy order to disorder at about 600 K. The phase separation and the Fe-vacancy ordering in the superconducting materials of KxFe2-ySe2 (0.2 ≤y ≤ 0.3) has been briefly discussed.

Mechanical properties, miscibility, thermal stability, and rheology of poly(propylene carbonate) and poly(ethylene-co-vinyl acetate) blends

Biodegradable polymeric blends are expected to be widely used by industry due to their environmental friendliness and comparable mechanical and thermal properties. In this study, blends of poly(propylene carbonate) (PPC) and poly(ethylene-co-vinyl acetate) (EVA) were prepared. Fourier transform infrared (FTIR) analysis revealed that there were some possible specific interactions between PPC and EVA. The differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results showed a single temperature peak of Tg between that of pure PPC and that of pure EVA, which suggested that PPC and EVA were compatible. Because of the interfacial interaction between PPC and EVA, EVA could greatly improve the tensile strength, the glass transition temperature and the thermal stability of PPC matrix. Rheological investigation demonstrated that there was a significantly dependence of viscosity on composition. When the EVA content increased, the viscosity began to increase. The PPC/EVA blends could be used as a common biodegradable material for a wide application.

Effect of oxygen stoichiometry in LuFe2O4−δ and its microstructure observed by aberration-corrected transmission electron microscopy

A series of oxygen deficient LuFe(2)O(4-δ) materials have been prepared under a controlled oxygen partial-pressure atmosphere. Measurements of magnetization reveal that the increase of oxygen deficiencies could evidently depress the ferrimagnetic phase transition temperature (T(N)). In additional to the well-known charge ordering within the (11(-)0) crystal plane, a visible structural modulation with q = (0,1/4.2,7/8) commonly appears on the (100) plane in the oxygen deficient samples. An aberration-corrected transmission electron microscopy study on the oxygen deficient samples demonstrates the presence of oxygen vacancies and local structural distortion. The atomic structural features in correlation with the structural modulation, distortion of the FeO(5) polyhedron and the (001) twinning domains have been also examined.

Mechanical properties, hydrophobic properties and thermal stability of the biodegradable poly(butylene adipate-co-terephthalate)/maleated thermoplastic starch blown films

Poly(butylene adipate-co-terephthalate) (PBAT) and thermoplastic starch (TPS) were blended by using maleic anhydride (MA) as a compatibilizer. Preferentially, TPS could be reacted with MA to obtain maleated thermoplastic starch (MTPS). Then PBAT/MTPS blends were blown films using blown technique. From dynamic mechanical analysis, the shifting of the glass transition temperatures toward each other suggested that PBAT was partially miscible with MTPS. From wide angle X-ray diffraction analysis, the degree of crystallinity of PBAT/MTPS films was decreased with increasing MTPS content. From rheological measurements, the melt elasticity and viscosity of the PBAT/MTPS blends increased. It was benefit to extrude blend and blow film. The contact angle values of bipolar liquid water were range from 100.2 to 77.7 ° decreased with increasing MTPS content from 0 to 50 %. The PBAT/MTPS films could satisfy the requirement for applying in our life.

Rheological, thermal and mechanical properties of biodegradable poly(propylene carbonate)/polylactide/Poly(1,2-propylene glycol adipate) blown films

Poly(propylene carbonate) (PPC) was blended with polylactide (PLA) and poly(1,2-propylene glycol adipate) (PPA) using a twin screw extruder. Then the PPC/PLA/PPA films were prepared using the blown film technique. DMA results showed that PPA could act as a plasticizer and improve the miscibility between PPC and PLA. Crystal morphology displayed that blending PLA with the amorphous PPC led to a decrease of the spherulite size of PLA. The results of mechanical tests indicated that PPC-rich films showed high elongation at break and PLA-rich films showed high tear strength and good optical properties. The content of PPC and PLA significantly affected the physical properties of the films. With increasing PPC content, the melt strengths of the PPC/PLA/PPA films were enhanced. These findings contributed to the biodegradable materials application for designing and manufacturing polymer packaging.

Cu/Te substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2

Two series of K0.8Fe1.75−xCuxSe2 () and K0.8Fe1.75Se2−yTey () single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation coexisting with the superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation.

Diethylene glycol monobutyl ether adipate as a novel plasticizer for biodegradable polylactide

Polylactide (PLA) was successfully plasticized by blending with diethylene glycol monobutyl ether adipate (DGBEA). The results showed that PLA and DGBEA had close solubility parameters, so PLA was miscible with DGBEA. The dynamic storage modulus and complex viscosity in the melt state of the blends decreased compared with neat PLA. DGBEA lowered the glass transition temperature and the cold crystallization temperature of PLA which were good indications of the extent of the plasticizing effect provided by DGBEA. However, the crystallinity and spherulite size of PLA gradually increased with increasing DGBEA content. In all PLA/plasticizer blends investigated, a stepwise change in the mechanical properties of the system was observed. The elongation at break and impact strength drastically increased, whereas tensile strength and modulus decreased. The DGBEA plasticizer had low tendency to migrate. Thus, the DGBEA was a promising plasticizer alternative for bioplastics as they also retained the biodegradable nature of these biobased materials.

The simultaneous introduction of low and high molecular weight of biodegradable Poly(diethylene glycol adipate)s to Plasticize and Toughen Polylactide

Plasticization and toughness of polylactide (PLA) are of interesting due to its poor machinability and brittleness. Here, low and high macromolecular weight of Poly(diethylene glycol adipate)s (L-PDEGA and H-PDEGA) were used to plasticize and toughen PLA simultaneously. The results showed that the mechanical properties of PLA remained almost unchanged when only 5 wt% L-PDEGA was added. However, H-PDEGA were effective in lowering the glass transition temperatures as well as in increasing the elongation at break and the impact strength. Compared with neat PLA, the crystallinity of PLA increased with increasing H-PDEGA content. When 20 wt% H-PDEGA was added, the impact strength and the elongation at break increased from 3.1 kJ/m2 and 5.6 % of neat PLA to 68.3 kJ/m2 to 272.4 %, respectively. Additionally, morphological study revealed that the fracture behavior of PLA had been changed from brittle to ductile after H-PDEGA incorporated. The results of rheological analysis showed that the storage modulus and complex viscosity in the melt state of the blends were decreased compared with that of neat PLA.

Microstructural properties of K0.8 Fe1.6 S2, K0.8 Fe1.75 Se2-y Sy(0???y???2) and K0.8 Fe1.5+x S2(0?<?x???0.5) single crystals

The structural features of the antiferromagnetic K0.8Fe1.6S2 have been studied in the temperature range from 300K up to 700K by means of in situ transmission electron microscopy (TEM). The superstructure with a wave vector q(1) = 1/5(3a* + b*) originating from a Fe-vacancy order has been clearly observed; moreover, the structural analysis shows that K0.8Fe1.6S2 undergoes a transition from the Fe-vacancy order to disorder at about 585K. The S substitution effect on the phase separation and superconductivity in the K0.8Fe1.75Se2-ySy materials has been systematically investigated by SEM and TEM structural analyses, as well as by electrical resistivity measurements. Our experimental results reveal that the S element adopts a homogeneous distribution in all investigated materials, and the essential phase-separation nature is very similar to what was observed in the K0.8Fe1.75Se2 superconductor. A phase-separated state formed by the coexistence of two Fe-vacancy orders with wave vectors q(1) = 1/5(3a*+b*) and q(3) = 1/4(3a*+b*) in K0.8Fe1.5+xS2 (0 < x < 0.1) has been briefly discussed. Copyright (C) EPLA, 2013

Oxygen-vacancy ordering in multiferroic Bi1?xCaxFeO3?x/2 (0.1???x???0.5)

Multiferroic Bi1-xCaxFeO3-x/2 (0.1 <= x <= 0.5) materials have been synthesized via a high-temperature sintering method. The structural properties have been studied using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The EELS measurements reveal that the oxidation state of Fe ions in these compounds is Fe+3, and oxygen vacancies are created as Ca substitutions for Bi. A series of superstructure modulations appear along the a-axis direction, and their wavelength can be written as L = na (n = 4, 5, 6 and 7) depending on the Ca contents. Based on our structural analysis, we interpret these superstructures in terms of oxygen-vacancy ordering associated with local structural distortions. Copyright (C) EPLA, 2013