Marta Suárez

A strong magneto-optical activity in rare-earth La3+ substituted M-type strontium ferrites

M-type strontium ferrites with substitution of Sr2+ by rare-earth La3+ were prepared by conventional ceramic technology. The structure, magnetic properties, and magneto-optical Kerr activity of Sr1−xLaxFe12O19 (x = 0, 0.05, 0.10, 0.15, 0.20) were investigated by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and magneto-optical ellipsometry, respectively. X-ray diffraction showed that the samples sintered at 1290 °C for 3 h were single M-type hexagonal ferrites. The magnetic properties were remarkably changed due to the valence change of Fe ions induced by the substitution of La ions. Most significantly, an important magneto-optical activity was induced in the La3+ substituted M-type strontium ferrites around 3 eV.

Sintering to Transparency of Polycrystalline Ceramic Materials

There is currently a high demand for advanced materials for different types of applications (see Fig. 1.1) in which besides a high mechanical performance, a partial or total transparency in a given spectral range is required. Transparent ceramics become more and more important for applications in which materials are subject to extremely high mechanical and thermal stress in combination with optical properties. More recently, interest has focused on the development of transparent armor materials (ceramic) for both military and civil applications. Also, the development of new optoelectronic devices has extended the use of ordinary optical materials to new applications and environments such as temperature (IR) sensor, optical fiber communications, laser interferometers, etc. A considerable fraction of these new devices operates in aggressive environments, such as ovens, radiation chambers and aerospace sensors. In such cases, the sensitive electronic component must be preserved from the extreme external condition by a transparent window. Transparent and coloured ceramics are also often used as wear and scratch resistant parts such as bearings and watch glasses as well as for their aesthetic Properties in synthetic opals and rubies.

Triruthenium carbonyl clusters derived from chiral aminooxazolines: synthesis and catalytic activity

Treatment of [Ru3(CO)12] with the chiral aminooxazolines (+)-2-amino-(4R)-phenyl-2-oxazoline (H2amphox), (+)-2-amino-(4R,5S)-indanyl-2-oxazoline (H2aminox) and (+)-2-(2-anilinyl)-(4R,5S)-indanyl-2-oxazoline (H2aninox) in THF at reflux temperature, affords the complexes [Ru3(mu-H)(mu3-kappa2-Hox-N,N)(CO)9] (H2ox = H2amphox, 1; H2aminox, 2) and [Ru3(mu-H)(mu-kappa2-Haninox-N,N)(CO)9] (3). In all cases, the activation of an N-H bond has occurred and the resulting amido fragment spans an edge of the metal triangle, while the N atom of the oxazoline ring is attached to the remaining metal atom (as in 1 and 2), or to one of the metal atoms of the bridged edge (as in 3). The use of 1-3 as catalyst precursors in the asymmetric hydrogen-transfer reduction of acetophenone and in the asymmetric cycloaddition of cyclopentadiene and acroleine is reported.

Textural properties of α-titanium(IV) phenylphosphonate: influence of preparation conditions

Abstract Layered α-titanium(IV) phenylphosphonate can be prepared with a broad variation in surface area and porosity. Several sources for tetravalent titanium ion and different synthetic procedures have been studied. The solids were characterized by powder X-ray diffraction (XRD), thermogravimetric (TG) analysis, IR and 31 P magic angle spinning (MAS) NMR spectroscopies, N 2 adsorption–desorption isotherms, and scanning electron microscopy (SEM). The materials obtained have a high thermal stability as shown by TG analysis. N 2 adsorption–desorption isotherms of the solids correspond to type IV of the BDDT classification and show hysteresis loops of type H-3, characteristic of solids with slit-shaped pores. The materials are essentially mesoporous, and any mensurable microporosity was not detected. BET surface areas, porosity, and crystallinity are markedly dependent on the preparation procedure.

Formation of Cyclopentadienyl and Ruthenacyclopentadienyl Derivatives through Ynenyl–Diyne and Ynenyl–Alkyne Couplings onto a Triruthenium Cluster Core

The compound [Ru3(mu-H)(mu3-eta2-ampy)(CO)9] (1; Hampy =2-amino-6-methylpyridine) reacts with diynes RC4R in THF at reflux temperature to give the ynenyl derivatives [Ru3(mu3-eta2-ampy)(mu-eta3-RC...CC-CHR)(mu-CO)2-(CO)6] (2: R=CH2OPh; 3: R=Ph). These products contain a 1,4-disubstituted butynen-3-yl ligand attached to two ruthenium atoms. The compound [Ru3(mu-eta2-ampy)[mu3-eta6-PhCC5(C...CPh)-HPh2](CO)7] (4), which contains an eta5-cyclopentadienyl ring and a bridging carbene fragment, has also been obtained from the reaction of 1 with diphenylbutadiyne. This compound arises from a remarkable [3+2] cycloaddition reaction of a preformed 1,4-diphenylbutynen-4-yl ligand with a triple bond of a second diphenylbutadiyne molecule. The reactivity of the ynenyl derivatives 2 and 3 with diynes and alkynes has been studied. In all cases, compounds of the general formula [Ru3(mu-eta2-ampy)[mu3-eta5-C(=CHR)C=CRCR1=CR2](CO)7] (5-17) have been obtained. They all contain a ruthenacyclopentadienyl fragment formed by coupling of the coordinated ynenyl ligand of 2 (R = CH2OPh) or 3 (R = Ph) with a triple bond of the new reagent (the CR1=CR2 fragment results from the incoming diyne or alkyne reagent). While most of the products derived from 2 have the alkenyl C=CHR fragment with a Z configuration (R cis to Ru), all the compounds obtained from 3 have this fragment with an E configuration. Except 2 and 3, all the cluster complexes described in this article have a five-electron donor ampy ligand attached to only two metal atoms, a coordination mode unprecedented in cluster chemistry.

Polyhydrated phases in the exchange of H+ and K+ in α-titanium phosphate

The exchange of H+ by K+ in α-titanium phosphate, Ti(HPO4)2·H2O, was studied. The exchange isotherm and the hydrolysis and titration curves were obtained, and the evolution of the material was followed by X-ray diffraction. The existence of partially substituted phases was not detected. Phases saturated in potassium and highly hydrated, Ti(KPO4)2·3H2O (interlayer distance 10.4 A) and Ti(KPO4)2·2H2O (9.6 A), were obtained. The experimental results are explained by taking account of the structures of the materials.

Reactivity of [Ru3(μ3-NPh)(μ3-CO)(CO)9] towards Activated Alkynes and Diynes − Isolation of a Trinuclear Intermediate During the Formation of Bi- and Tetranuclear Products

Treatment of the trinuclear imido-bridged cluster compound [Ru3(μ3-NPh)(μ3-CO)(CO)9] (1) with activated alkynes (methyl propynoate and methyl phenylpropynoate) and diynes (diphenylbutadiyne, 2,4-hexadiyne, 1,6-diphenyloxy-2,4-hexadiyne, and 1-trimethylsilyl-1,4-pentadiyne) in hexanes at reflux temperature leads to separable mixtures of the tetranuclear and binuclear derivatives [Ru4(μ4-NPh)(μ4,η2-RC≡CR′)(μ-CO)2(CO)9] and [Ru2{μ,η3-RC=CR′C(O)NPh}(CO)6], respectively. While the former complexes feature a phenylimido ligand in a rather rare μ4-coordination mode, the binuclear compounds contain acrylamido ligands that result from the coupling of a CO ligand and the original phenylimido ligand of 1 with the incoming alkyne or diyne. Surprisingly, all the products derived from diynes contain a pendant (non-coordinated) alkyne functionality. The isolation of the trinuclear derivative [Ru3(μ3-NPh)(μ3,η2-PhC≡CC≡CPh)(CO)9] (9) in the reaction of 1 with diphenylbutadiyne and the fact that its thermolysis leads to a mixture of [Ru4(μ4-NPh)(μ4,η2-PhC≡CC≡CPh)(μ-CO)2(CO)9] and [Ru2{μ,η3-C(C≡CPh)=C(Ph)C(O)NPh}(CO)6] support the proposal that trinuclear species containing coordinated alkyne or diyne ligands, similar to 9, are intermediates in the synthesis of all the bi- and tetranuclear products. Only one of the two possible regioisomers of each product (that might have arisen from the asymmetry of the alkyne or diyne reagents used) is formed. The origin of this regioselectivity is also discussed.

Dielectric behavior of ceramic–graphene composites around the percolation threshold

Al2O3/graphene and BaTiO3/graphene composites with different concentrations of the conductive second phase, both below and above the percolation threshold, were prepared by the traditional ceramic processing route followed by spark plasma sintering. It is shown that the addition of graphene pins the grain growth of the ceramic matrix grains, leading to a change of the microstructure at low filler concentrations. As a consequence, the composites exhibit two percolation thresholds and their dielectric properties are not only determined by the dielectric properties of the constituents and their relative fractions but also the microstructure of the composite must be considered. Additionally, a giant increase of the dielectric constant has been found around the percolation thresholds in barium titanate–graphene composites. In particular, values of the dielectric constant up to 45,000 and 15,000 were found at 1 kHz in composites containing 0.4 and 0.6 wt. % graphene, respectively.

Stock market response to the formation of global alliances: evidence from Spanish corporations

This paper analyzes the stock market reaction to global alliance formation in the Spanish context. For the purposes of this study, global alliances are those which are established with international partners in order to coordinate actions in several countries, seeking the development of complementary relationships on a global scale. Using a sample of 72 global alliances formed between 1987 and 1997 by Spanish firms listed on the Madrid Stock Exchange, it shows that the Spanish firms gained an average abnormal return of 0.2 percent on the day of the announcement.

X-ray diffraction spectrometry in lamellar ion-exchangers for the analysis of the substitution phases with thermal splitting

X-Ray diffraction in the quantitative analysis of crystalline solid phases is used. The evolution of γ-titanium phosphate in the H+Ca2+ ion exchange is reported. The crystalline phase: TiH1.25Ca0.37(PO4)2 · 3.5H2O, which splitts in the Ti(HPO4)2 and TiHCa0.5(PO4)2 phases at temperatures higher than 220°C, is characterized. This splitting is the support to propose a method, only using diffractometric data, in order to obtain the relationship of proportionality between the concentration of the crystalline phases in the mixture and the relative intensity of the diffraction lines originated. The analysis method described in this paper can be used for the study of lamellar materials with similar behavior to the one of the γ-titanium phosphate.