Certification of the Specific Micropore Volume and the Median Micropore Width of Two Microporous Reference Materials According to Draft-DIN 66135-4, BCR-704, BCR-705.

Abstract not availableJRC.D-Institute for Reference Materials and Measurements (Geel

Spin glass in semiconducting KFe 1.05_{1.05} Ag 0.88_{0.88} Te 2_{2} single crystals

We report discovery of KFe1.05Ag0.88Te2 single crystals with semiconducting spin glass ground state. Composition and structure analyses suggest nearly stoichiometric I4/mmm space group but allow for the existence of vacancies, absent in long-range semiconducting antiferromagnet KFe0.85Ag1.15Te2. The subtle change in stoichometry in Fe-Ag sublattice changes magnetic ground state but not conductivity, giving further insight into the semiconducting gap mechanism

Elasticity and magnetocaloric effect in MnFe4_{4}Si3_{3}

The room temperature magnetocaloric material MnFe4Si3 was investigated with nuclear inelastic scattering (NIS) and resonant ultrasound spectroscopy (RUS) at different temperatures and applied magnetic fields in order to assess the influence of the magnetic transition and the magnetocaloric effect on lattice dynamics. The NIS data give access to phonons with energies above 3 meV, whereas RUS probes the elasticity of the material in the MHz frequency range and thus low-energy, ∼ neV, phonon modes. A significant influence of the magnetic transition on the lattice dynamics is observed only in the low-energy, long-wavelength limit. MnFe4Si3 and other compounds in the Mn5−xFexSi3 series were also investigated with vibrating sample magnetometry, resistivity measurements, and Mössbauer spectroscopy in order to study the magnetic transitions and to complement the results obtained on the lattice dynamic

Natural ageing of Al Cu Mg revisited from a local perspective

Although Al alloys based on the Al-Cu-(Mg) system have been investigated for decades, information about the evolution of microstructure on the atomistic level during natural ageing is scarce. Therefore, the early stages of natural ageing in laboratory Al-Cu-(Mg) alloys and in AA2024 were investigated using positron annihilation and X-ray absorption spectroscopy. This complementary approach allows for accessing both essential components of Al alloys, namely vacancies and alloying elements. It is found, that during natural ageing the chemical environment of vacancies is formed both of Cu and Mg atoms and that the rearrangement of vacancy surroundings persists the hardness increase of Al-Cu-Mg alloys. During natural ageing two different regimes of vacancy environment are detected and interpreted in terms of cluster growth and vacancy capture. Features of the near edge structure of the X-ray absorption are interpreted using theoretical calculations obtained by the FEFF8.4 c ode. Thus the agglomeration of Cu and Mg, which is accompanied by lattice distortions around Cu atoms, can be probed. A minimal size of Cu-Mg co-clusters is proposed for later stages of natural ageing

Positron lifetime study of the formation of vacancy clusters and dislocations in quenched Al, Al Mg and Al Si alloys

The clustering kinetics in quenched pure Al, binary Al Mg and binary Al Si alloys were studied by positron annihilation lifetime spectroscopy PALS and differential scanning calorimetry DSC during natural ageing NA . Shortly after quenching, positrons annihilate either in the bulk material or in vacancy type defects such as mono vacancies in Al and vacancy solute complexes in Al Mg and Al Si alloys . Upon NA, vacancy clusters of various sizes and number densities are formed. In Al, such clusters contain typically 3 vacancies. In Al Mg and Al Si alloys, complexes containing various vacancies and also solute atoms are formed. The presence of shallow positron traps was detected in temperature dependent positron lifetime experiments. They were identified as quenched in dislocations rather than Mg or Si clusters as no solute clustering signal during NA was observed in DSC runs of the binary Al Mg and Al Si alloy

Quenching rattling modes in skutterudites with pressure

A high-pressure study of the lattice dynamics in the filled skutterudite Eu0.84Fe4Sb12 was carried out by means of x-ray powder diffraction and nuclear inelastic scattering. The anharmonicity of particular phonon modes was characterized by mode and element specific Grüneisen parameters. The large anharmonicity of the rattling optical mode that is hybridized with the acoustical phonons at ambient pressure is reduced at high pressure as the phonon modes decouple. This result suggests that anharmonic coupling between acoustic and optical phonon modes plays a central role in the reduced thermal conductivity