Les Syst�mes B2O3?MO?MS Boracites M?S (M = Mg, Mn, Fe, Cd) et Sodalites M?S (M = Co, Zn)

High-pressure synthesis of borate-nitrates: crystal structure of M 3B7O13(NO3) (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+)

The orthorhombic nitrate-boracites with the sum formula M 3B7O13NO3 (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+) were synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 6 GPa and 800 °C, respectively. The crystal structures of the five isotypic substances, which crystallize in the space group Pca21, were determined via single-crystal X-ray diffraction and the structural features of the incorporated nitrate anions are discussed.

Injection and controlled motion of conducting domain walls in improper ferroelectric Cu-Cl boracite

Ferroelectric domain walls constitute a completely new class of sheet-like functional material. Moreover, since domain walls are generally writable, erasable and mobile, they could be useful in functionally agile devices: for example, creating and moving conducting walls could make or break electrical connections in new forms of reconfigurable nanocircuitry. However, significant challenges exist: site-specific injection and annihilation of planar walls, which show robust conductivity, has not been easy to achieve. Here, we report the observation, mechanical writing and controlled movement of charged conducting domain walls in the improper-ferroelectric Cu₃B₇O₁₃Cl. Walls are straight, tens of microns long and exist as a consequence of elastic compatibility conditions between specific domain pairs. We show that site-specific injection of conducting walls of up to hundreds of microns in length can be achieved through locally applied point-stress and, once created, that they can be moved and repositioned using applied electric fields.

The Chemistry and Packaging of Nanocomposite Confined Arrays

The miniaturization of electronic and optic devices has revolutionized response times, energy loss and transport efficiency. An additional bonus is that as one approaches the nanosize regime the presence or absence of a few atoms and the geometrical disposition of each atom can significantly modify electronic and photonic properties. This control can be further supplemented by “packaging” assemblies of atoms or molecules into thin film or nanocomposite bulk materials to define surface states, cluster environment and geometry, intercluster interactions, and consequently, a wide tunable range of optical and charge carrier responses.

The chemist is presented with an intriguing challenge. First the clusters must be unisized with identical geometries. Secondly, the atom or molecular assemblies should ideally have perfect periodicity in order to rigorously define optoelectronic densities and intercluster tunnelling. A third requirement is that the nanocomposite be processable, generally in the form of thin films or single crystals. Numerous approaches are being undertaken in achieve these goals, including molecular beam and atomic layer epitaxy, molecular sieve inclusion chemistry, molecular capping of inorganic clusters, porous glass and aerosol synthesis. This paper presents a brief review of the interface chemistry associated with nanophase confinement and packaging and some features of three dimensional surface confinement using molecular sieves and zeolites.

Quantum confinement and host/guest chemistry: probing a new dimension

Nanoparticulate metals and semiconductors that have atomic arrangements at the interface of molecular clusters and "infinite" solid-state arrays of atoms have distinctive properties determined by the extent of confinement of highly delocalized valence electrons. At this interface, the total number of atoms and the geometrical disposition of each atom can be used to significantly modify the electronic and photonic response of the medium. In addition to teh novel inherent physical properties of the quantum-confined moieties, their "packaging" into nanocomposite bulk materials can be used to define the confinement surface states and environment, intercluster interactions, the quantum-confinement geometry, and the effective charge-carrier density of the bulk. Current approaches for generating nanostructures of conducting materials are briefly reviewed, especially the use of three-dimensional crystalline superlattices as hosts for quantum-confined semiconductor atom arrays (such as quantum wires and dots) with controlled inter-quantum-structure tunneling.