Novel characterization of the adsorption sites in large pore metal-organic frameworks: combination of X-ray powder diffraction and thermal desorption spectroscopy.

The preferred adsorption sites of xenon in the recently synthesized metal-organic framework MFU-4l(arge) possessing a bimodal pore structure (with pore sizes of 12 Å and 18.6 Å) were studied via the combination of low temperature thermal desorption spectroscopy and in situ X-ray powder diffraction. The diffraction patterns were collected at 110 K and 150 K according to the temperature of the desorption maxima. The maximum entropy method was used to reconstruct the electron density distribution of the structure and to localize the adsorbed xenon using refined data of the Xe-filled and empty sample. First principles calculations revealed that Xe atoms exclusively occupy the Wyckoff 32f position at approximately 2/3 2/3 2/3 along the body diagonal of the cubic crystal structure. At 110 K, Xe atoms occupy all 32 f positions (8 atoms per pore) while at 150 K the occupancy descends to 25% (2 atoms per pore). No Xe occupation of the small pores is observed by neither experimental measurements nor theoretical studies.

trans-Bis(acetato-κO)bis-(2-amino-ethanol-κ(2)N,O)nickel(II).

In the title compound, [Ni(CH(3)CO(2))(2)(C(2)H(7)NO)(2)], the Ni(II) cation, located on an inversion center, is N,O-chelated by two 2-amino-ethanol mol-ecules and further coordinated by two monodendate acetate anions in a slightly distorted octa-hedral geometry. The latter is stabilized by intra-molecular O-H⋯O hydrogen bonds involving the non-coordinated O atom of the acetate and the H atom of the hy-droxy group of the 2-amino-ethanol ligand. In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into a three-dimensional supra-molecular framework that involves (a) the coordinated acetate O atom and one of the H atoms of the amino group and (b) the non-coordinated acetate O atom and the other H atom of the amino group.

Towards laser printing of magnetocaloric structures by inducing a magnetic phase transition in iron-rhodium nanoparticles.

The development of magnetocaloric materials represents an approach to enable efficient and environmentally friendly refrigeration. It is envisioned as a key technology to reduce CO2 emissions of air conditioning and cooling systems. Fe-Rh has been shown to be one of the best-suited materials in terms of heat exchange per material volume. However, the Fe-Rh magnetocaloric response depends on its composition. Hence, the adaptation of material processing routes that preserve the Fe-Rh magnetocaloric response in the generated structures is a fundamental step towards the industrial development of this cooling technology. To address this challenge, the temperature-dependent properties of laser synthesized Fe-Rh nanoparticles and the laser printing of Fe-Rh nanoparticle inks are studied to generate 2D magnetocaloric structures that are potentially interesting for applications such as waste heat management of compact electrical appliances or thermal diodes, switches, and printable magnetocaloric media. The magnetization and temperature dependence of the ink's γ-FeRh to B2-FeRh magnetic transition is analyzed throughout the complete process, finding a linear increase of the magnetization M (0.8 T, 300 K) up to 96 Am2/kg with ca. 90% of the γ-FeRh being transformed permanently into the B2-phase. In 2D structures, magnetization values of M (0.8 T, 300 K) ≈ 11 Am2/kg could be reached by laser sintering, yielding partial conversion to the B2-phase equivalent to long-time heating temperature of app. 600 K, via this treatment. Thus, the proposed procedure constitutes a robust route to achieve the generation of magnetocaloric structures.

Direct observation of paramagnetic spin fluctuations in LaFe13-x Si x.

Spin fluctuations are a crucial driving force for magnetic phase transitions, but their presence usually is indirectly deduced from macroscopic variables like volume, magnetization or electrical resistivity. Here we report on the direct observation of spin fluctuations in the paramagnetic regime of the magnetocaloric model system LaFe11.6Si1.4 in the form of neutron diffuse scattering. To confirm the magnetic origin of the diffuse scattering, we correlate the temperature dependence of the diffuse intensity with ac magnetic susceptibility and x-ray diffraction experiments under magnetic field. Strong spin fluctuations are already observable at 295 K and their presence alters the thermal contraction behavior of LaFe11.6Si1.4 down to the Curie temperature of the first-order magneto-structural transition at 190 K. We explain the influence of the spin fluctuation amplitude on the lattice parameter in the framework of the internal magnetic pressure model and find that the critical forced magnetostriction follows Takashi's spin fluctuation theory for itinerant electron systems.

From average to local structure: a Rietveld and an atomic pair distribution function (PDF) study of selenium clusters in zeolite-NdY.

The structure of Se particles in the approximately 13 A diameter alpha-cages of zeolite NdY has been determined by Rietveld refinement and pair distribution function (PDF) analysis of X-ray data. With the diffuse scattering subtracted an average structure comprised of an undistorted framework containing nanoclusters of 20 Se atoms is observed. The intracluster correlations and the cluster-framework correlations which give rise to diffuse scattering were modeled by using PDF analysis.

Electrical and Structural Origin of Self-Healing Phenomena in Pentacene Thin Films.

Self-healing induced by structural phase transformation is demonstrated using pentacene field-effect transistors. During the self-healing process, the electrical properties at the pentacene interfaces improve due to the phase transformation from monolayer phase to thin-film phase. Enhanced mobility is confirmed by first-principles calculations.

Piezoelectricity and rotostriction through polar and non-polar coupled instabilities in bismuth-based piezoceramics.

Coupling of order parameters provides a means to tune functionality in advanced materials including multiferroics, superconductors, and ionic conductors. We demonstrate that the response of a frustrated ferroelectric state leads to coupling between order parameters under electric field depending on grain orientation. The strain of grains oriented along a specific crystallographic direction, 〈h00〉, is caused by converse piezoelectricity originating from a ferrodistortive tetragonal phase. For 〈hhh〉 oriented grains, the strain results from converse piezoelectricity and rotostriction, as indicated by an antiferrodistortive instability that promotes octahedral tilting in a rhombohedral phase. Both strain mechanisms combined lead to a colossal local strain of (2.4 ± 0.1) % and indicate coupling between oxygen octahedral tilting and polarization, here termed "rotopolarization". These findings were confirmed with electromechanical experiments, in situ neutron diffraction, and in situ transmission electron microscopy in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3. This work demonstrates that polar and non-polar instabilities can cooperate to provide colossal functional responses.

High mobility indium zinc oxide thin film field-effect transistors by semiconductor layer engineering.

Indium zinc oxide thin-film transistors are fabricated via a precursor in solution route on silicon substrates with silicon dioxide gate dielectric. It is found that the extracted mobility rises, peaks, and then decreases with increasing precursor concentration instead of rising and saturating. Investigation with scanning probe techniques reveals full thickness variations within the film which are assumed to adversely affect charge transport. Additional layers are coated, and the extracted mobility is observed to increase up to 19.7 cm(2) V(-1) s(-1). The reasons for this are examined in detail by direct imaging with scanning tunneling microscopy and extracting electron density profiles from X-ray reflection measurements. It is found that the optimal concentration for single layer films is suboptimal when coating multiple layers and in fact using many layers of very low concentrations of precursor in the solution, leading to a dense, defect and void free film, affording the highest mobilities. A consistent qualitative model of layer formation is developed explaining how the morphology of the film develops as the concentration of precursor in the initial solution is varied.