Elastic properties of dilute palladium-hydrogen solid solutions

A thin-line pulse-echo technique has been used to measure the variation of the Young's modulus of super-pure palladium as a function of temperature and hydrogen concentration. The resulting measurements have been analyzed so as to yield approximate information relating to the change to be expected in the partial thermodynamic functions of the system due to the lattice relaxation at constant pressure.     

Supershell structure in alkali metal nanowires

Nanowires are formed by indenting and subsequently retracting two pieces of sodium metal. Their cross section gradually reduces upon retraction and the diameters can be obtained from the conductance. In previous work we have demonstrated that when one constructs a histogram of diameters from large numbers of indentation-retraction cycles such histograms show a periodic pattern of stable nanowire diameters due to shell structure in the conductance modes. Here, we report the observation of a modulation of this periodic pattern, in agreement with predictions of a supershell structure.     

Linked Supramolecular Building Blocks for Enhanced Cluster Formation

Methylene‐bridged calix[4]arenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis‐calix[4]arenes and transition metal ions or 3d‐4f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.     

Facile Interchange of 3d and 4f Ions in Single‐Molecule Magnets: Stepwise Assembly of [Mn4], [Mn3Ln] and [Mn2Ln2] Cages within Calix[4]arene Scaffolds

The central Mn^II ions in a series of calix[4]arene‐stabilised butterflies can be sequentially replaced with Ln^III ions, maintaining the structural integrity of the molecule but transforming its magnetic properties. The replacement of Mn^II for Gd^III allows for the examination of the transferability of spin‐Hamiltonian parameters within the family as well as permitting their reliable determination. The introduction of the 4f ions results in weaker intramolecular magnetic exchange, an increase in the number of low‐lying excited states, and an increase in magnetisation relaxation, highlighting the importance of exchange over single‐ion anisotropy for the observation of SMM behaviour in this family of complexes. The presence of the [TM^II/III(TBC[4])(OH)(solvent)] metalloligand (TM=transition metal, TBC=p‐tBu‐calix[4]arene) suggests that magnetic calix[n]arene building blocks can be employed to encapsulate a range of different “guests” within structurally robust “hosts”.     

Quantum mechanics: cleaning up metaphysical baggage

The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed.     

Thermodynamics of ternary Fe-Co-N austenites

Gas-solid equilibrium measurements have been used to determine the variation with cobalt concentration in the range 0–9 at. % Co of the partial molar enthalpies and excess entropies in ternary Fe-Co-N austenites in the temperature range 1173–1503 K. The resulting thermodynamic data show a relative invariance in these thermodynamic functions in excellent accord with the cell model for ternary solid solutions containing a substitutional and an interstitial species in which the presence of the substitutional species creates “antitrapping” sites for interstitial atoms.     

Chemical diffusion in interstitial solid solutions

A model has been set up to account for the variation of diffusivity with composition in the case of interstitial chemical diffusion in the presence of a solute atom gradient. It is shown that the magnitude of the gradient does not affect the diffusivity, provided that it is not very steep. The differential effect of the gradient of specific volume resulting from the species gradient on the jump frequency is taken into account. The predictions of the model are compared with kinetic data for carbon in f.c.c. iron measured both with and without a chemical concentration gradient.