Hybrid layer perovskites

PHYSICAL PROPERTIES AND APPLICATIONS OF HYBRID LAYER PEROVSKITES... 

Because of their interesting magnetic properties, hybrid layered perovskites containing transition metal ions were... 

Organic-perovskite hybrids play an important role in the fabrication of various nanodevices as well as in elucidating their fundamental properties. Intercalation of organic components into layered perovskites can be facilitated by various techniques such as ion exchange and the exfoliation-restacking method. In addition, the electrochemical intercalation method is also favorable for intercalation of organic molecules into transition metal oxides. However, except for... 

One of main thrusts in organic-perovskite hybrids has been in the preparation of stable delaminated perovskite sols as the building blocks of nanocomposite materials. A well-known process for exfoliation is to weaken the attractive interaction of the layers through intercalation of bulky organic components. A representative example is exfoliation of bismuth-based cuprate superconductors (Figure 14.12). °3... 

Modules of perovskite-type (abbreviated to perovskite) crystal structure alternating with other structural modules occur in several crystalline materials that are known as hybrid or intergrowth perovskites. Three-dimensional (3D - the octahedra share corners in three non-coplanar directions such that layers of thickness many octahedra are formed), two-dimensional (2D - the octahedra share corners in two directions such that layers of thickness one octahedron are formed), onedimensional (ID - the sharing of octahedral corners develops along one direction only such that rows of octahedra result) and zero-dimensional (OD - only isolated octahedra occur) perovskite layers are known. In the OD and ID layers, the positions of the isolated octahedra (OD) and rows of octahedra (ID) are supposed to match those of the octahedral framework in the perovskite structure. 

Fig. 5 (Left) The 5,5" -Z7/5(aminoethyl)-2,2 5, 2" 5",2 "-quaterthiophene molecule. (Center) perovskite structure of the (AEQT) PbBr4. (Right) (a) Cross section of the OILED device structure (not to scale) (b) view of the circular substrate containing four devices. For clarity, the OXD7 layer (on the top of the patterned hybrid perovskite layer) is not shown. (Adapted from Ref. [32].) (View this art in color at WWW,dekker.com.)...

In the layered Ruddlesden-Popper and Dion-Jacobson phases, improper ferroelectricity can also arise in a form termed hybrid improper ferroelectricity. Here, the ferroelectricity arises when two non-polar rotations of BO octahedra combine to produce a polar stmcture. The same effect may well also occur in the Aurivillius phases although this has not yet been proven. The creation of improper ferroelectric polarisation due to magnetic interactions in multiferroic perovskites is described in Section 7.10. 

The layered silicate most often used to improve the properties of PDMS is montmorillonite. 204-225 improvements have also been reported upon the introduction of graphite, graphite oxide,mica, fluoromica, hectorite, ° fiuorohectorite, laponite, wollastonite, perovskite, ° sepiolite, and titanium-niobium oxide. Kaolin and exfoliated layered double hydroxides have also been used in PDMS nanocomposites. In some cases, diphenylsiloxane-clay hybrids have been used to reinforce polyethylene. ... 

Lappas, A. Zorko, A. Wortham, E. Das, R. N. Giannelis, E. P. Cevc, P. Arcon, D., Clay-Low-Energy Magnetic Excitations and Morphology in Layered Hybrid Perovskite-Poly(dimethylsiloxane) Nanocomposites. Chem. Mater. 2005,17, 1199-1207. 

We discuss here in more detail the results of a hybrid HF-DFT LCAO comparative study of cubic SrZrO and SrTiOa (001) surface properties in the single-slab model [825). As known from [824], the consideration of systems with 7 8 atomic layers is sufficient to reproduce the essential surface properties of cubic perovskites. Three different slab models have been used in [825]. The first (I) and the second (II) ones consist of 7 crystalline planes (either SrO- or MO2-terminated, respectively) being symmetrical with respect to the central mirror plane but nonstoichiometric (see Fig. 11.4). The central layer is composed of MO2 (M = Ti, Zr) units in the model 1 and SrO units in the model 11. Both models 1 and 11 have been apphed for studying the surface properties of titanates by ab-initio calculations [832]. The asymmetric model 111 is stoichiometric and includes 4 SrO and 4 MO2 atomic planes. Accordingly, it is terminated by a SrO plane on one side and by a MO2 plane on the other side and there is no central atomic layer. The model 111 has been included in the simulation to investigate the influence of the stoichiometry-violation in the symmetrical models 1 and II on the calculated surface properties. For all slabs a 1 x 1 surface unit cell has been taken. For the 2D translations in slabs the experimental bulk lattice constants of SrZrOs (4.154 A) and SrTiOs (3.900 A) were used that does not differ significantly from DFT B3PW LCAO theoretical values (4.165 A and 3.910 A respectively). 

Perovskite layers can also be hybridized with metal phases or cermets (most often based on Ni) for promoting the electronic conductivity and stability of... 

---