Electric-field-induced paraelectric to ferroelectric phase transformation in prototypical polycrystalline BaTiO₃

An electric-field-induced paraelectric cubic to ferroelectric tetragonal phase transformation has been directly observed in prototypical polycrystalline BaTiO3 at temperatures above the Curie point (TC) using in situ high-energy synchrotron X-ray diffraction. The transformation persisted to a maximum temperature of 4-°C above TC. The nature of the observed field-induced transformation and the resulting development of domain texture within the induced phase were dependent on the proximity to the transition temperature, corresponding well to previous macroscopic measurements. The transition electric field increased with increasing temperature above TC, while the magnitude of the resultant tetragonal domain texture at the maximum electric field (4-kV mm-1) decreased at higher temperatures. These results provide insights into the phase transformation behavior of a prototypical ferroelectric and have important implications for the development of future large-strain phase-change actuator materials

A neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND 2 CD 2 COOD) 3 .D 2 SO 4

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND 2CD2COOD)3.D2SO4 is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below TC using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range - from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H-bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long-range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS - no low temperature anomalies were observed in the crystal structure. Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND 2CD2COOD)3.D2SO4 is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below TC using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range - from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H-bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long-range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS - no low temperature anomalies were observed in the crystal structure

Compositional dependence of disordered structures in Na ½ Bi ½ TiO 3 -BaTiO 3 solid solutions

Disordered structures contribute to the relaxor ferroelectric properties of the lead-free system Na½Bi½TiO3-(x)%BaTiO3. Such structures are difficult to characterize with conventional structural analysis techniques. Here, diffuse X-ray scattering was used to analyze the disordered structures from four single-crystals of Na½Bi½TiO3-(x)%BaTiO3, with compositions of (x)% = 0%, 4%, 9% and 17%. Such a range of compositions allowed a distinction between the structures that occur across the morphotropic phase boundary, where enhanced electro-mechanical properties have been reported. Throughout the compositional range, the resulting diffuse scattering showed the modification of correlated atomic displacements, transformation of planar defects in the oxygen octahedral tilt-systems, and the presence of modulations of approximately 10 unit cells. The results reported here demonstrate an evolution of the short-range structures across the morphotropic phase boundary that may underpin the electro-mechanical properties of Na½Bi½TiO3-(x)%BaTiO3. This information will ultimately assist in tailoring disordered structures for next-generation piezoelectric materials

NKp30 enables NK cells to act naturally with fungi

Item does not contain fulltextNK cells have direct activity against fungal pathogens. Using an unbiased systematic approach, Li et al. (2013) find that NKp30 is a major NK cell receptor responsible for fungal recognition. Moreover, diminished NKp30 expression is associated with reduced antifungal activity in NK cells isolated from HIV-infected persons

The evolution of crystalline ordering for ligand-ornamented zinc oxide nanoparticles

Recent total scattering experiments have opened up the possibility to study nanoparticle formation in situ and to observe the structural transformation from precursor clusters to adult particles. Organic ligand molecules interact with precursors of metal oxide nanoparticles, yet their influence onto the evolution of crystallinity during particle formation has not been addressed in detail; nor have in situ total scattering experiments ventured into the field of low-concentration, room-temperature syntheses in organic solvents to date. In this report, we follow the crystallization of ZnO nanoparticles in ethanol in the presence of different organic ligands. Low coordinated zinc precursor clusters rapidly polymerize upon base addition to particles of ca. 1 nm in diameter. In situ SAXS experiments reveal that the overall particle size increases to 2 to 4 nm with advancing reaction time. Complementary in situ PDF experiments show smaller crystalline domain sizes, which are only one third to half as large as the particle diameter. The ZnO particles thus feature a crystalline core surrounded by a disordered shell. Both, the core and the shell diameter are influenced by the different surface-bound organic ligands, which prevent an immediate relaxation to fully crystalline particles. A slow crystallization takes place in solution. We assume a dynamic equilibrium of the ligand and solvent molecules at the particle surface, which enables gradual bond restructuring. With suitably adjusted synthesis conditions, in our case by a continuous base addition, we show how to bypass the disordered intermediates, allowing the spontaneous nucleation of fully crystalline nanoparticles