Infrared spectra of some oxides of K2NiF4 and related structures

The i.r. spectra of some Ln2BO4 and LnSrBO4 compounds (Ln = La, Pr, Nd, Sm or Gd;B = Fe, Al, Co or Cu) with K2NiF4 or related structures have been studied in the range 800-300 cm−1. The BO6 octahedra in compounds with K2NiF4 structure are elongated. The assignment of the bands in terms of internal modes of sheets of bridged BO6 octahedra or square-planar BO4 sheets has been considered. The observed spectra are correlated with those of solid solutions of these oxides and of LnBO3 perovskites. Unusually high stretching frequencies found in some of the oxides are discussed in terms of the short B---O bonds in the basal plane and the Ln---O bonds along the c axis.

New A2+Mo4+O3 oxides with defect spinel structure

New A2+Mo4+O3 oxides for A = Mn, Co and Zn crystallizing in a defect spinel structure have been prepared by hydrogen-reduction of the corresponding AMoO4 oxides. X-ray powder diffraction intensity analysis of the zinc compound indicates that the cation distribution is (Zn)t[Zn1/3Mo4/3□1/3]oO4. The defect spinels are metastable decomposing to a mixture of A2Mo3O8 and AO at high temperatures. Electrical and magnetic properties of the spinel phases are reported.

Radical Enhanced Atomic Layer Deposition of Metals and Oxides

Atomic Layer Deposition (ALD) is a chemical, gas-phase thin film deposition method. It is known for its ability for accurate and precise thickness control, and uniform and conformal film growth. One area where ALD has not yet excelled is film deposition at low temperatures. Also deposition of metals, besides the noble metals, has proven to be quite challenging. To alleviate these limitations, more aggressive reactants are required. One such group of reactants are radicals, which may be formed by dissociating gases. Dissociation is most conveniently done with a plasma source. For example, dissociating molecular oxygen or hydrogen, oxygen or hydrogen radicals are generated. The use of radicals in ALD may surmount some of the above limitations: oxide film deposition at low temperatures may become feasible if oxygen radicals are used as they are highly reactive. Also, as hydrogen radicals are very effective reducing agents, they may be used to deposit metals. In this work, a plasma source was incorporated in an existing ALD reactor for radical generation, and the reactor was used to study five different Radical Enhanced ALD processes. The modifications to the existing reactor and the different possibilities during the modification process are discussed. The studied materials include two metals, copper and silver, and three oxides, aluminium oxide, titanium dioxide and tantalum oxide. The materials were characterized and their properties were compared to other variations of the same process, utilizing the same metal precursor, to understand what kind of effect the non-metal precursor has on the film properties and growth characteristics. Both metals were deposited successfully, and silver for the first time by ALD. The films had low resistivity and grew conformally in the ALD mode, demonstrating that the REALD of metals is true ALD. The oxide films had exceptionally high growth rates, and aluminium oxide grew at room temperature with low cycle times and resulted in good quality films. Both aluminium oxide and titanium dioxide were deposited on natural fibres without damaging the fibre. Tantalum oxide was also deposited successfully, with good electrical properties, but at slightly higher temperature than the other two oxides, due to the evaporation temperature required by the metal precursor. Overall, the ability of REALD to deposit metallic and oxide films with high quality at low temperatures was demonstrated.

Metal-insulator-semiconductor capacitors with bismuth oxide as insulator

Metal-insulator-semiconductor capacitors using aluminum Bi2O3 and silicon have been studied for varactor applications. Reactively sputtered Bi2O3 films which under suitable proportions of oxygen and argon and had high resistivity suitable for device applications showed a dielectric constant of 25. Journal of Applied Physics is copyrighted by The American Institute of Physics.

A Convenient Route for the Synthesis of Complex Metal Oxides Employing Solid-Solution Precursors

Synthesis of complex metal oxides by the thermal decomposition of solid-solution precursors (formed by isomorphous compounds of component metals) has been investigated since the method enables mixing of cations on an atomic scale and drastically reduces diffusion distances to a few angstroms. Several interesting oxides such as Ca2Fe03,5C, aCoz04,C a2C0205a, nd Ca,FeCo05 have been prepared by this technique starting from carbonate solid solutions of the type Ca,-,Fe,C03, Cal-,Co,C03, and Ca,-,,M,M'yC03 (M, M' = Mn, Fe, Co). The method has been extended to oxalate solid-solution precursors, and the possibility of making use of other kinds of precursor solid solutions is indicated.

Reaction of sulphuryl chlorofluoride with a few metals and metal oxides

Sulphuryl chlorofluoride has no observable reaction with metals and metal oxides at room temperature. Metals like copper, silver, iron, and zinc react with the chlorofluoride in the temperature range 200–400°C. Metal chlorides, metal fluorides and sulphur dioxide are the main products of these reactions. With the corresponding metal oxides, on the other hand, the respective metal sulphates are formed in addition to the metal chlorides and fluorides. In the case of lead and lead oxide, lead chlorofluoride is formed instead of lead chloride and lead fluoride. Sulphuryl fluoride is formed in small quantities in all these reactions by the decomposition of the chlorofluoride. Glass is not attacked by sulphuryl chlorofluoride below 500°C.

Ternary bismuth oxides Bi26â-xMxO40ay (M = Mg, Al, Co and Ni) related to α - Bi2O3

Reaction of Bi2O3 with MgO, NiO, Co3O4 and Al2O3 gives rise to the corresponding ternary bismuth oxides, Bi18Mg8O36, Bi18Ni8O36, Bi20Co6O39 and Bi24Al2O39. These oxides have the general formula Bi26�xMxO40�y and exhibit BCC structures related to α - Bi2O3. In the first three solids, the metal ions, M, replace bismuth randomly at the octahedral 24r sites (space group 123); in the last case, aluminium ions occupy the tetrahedral 2a sites, the phase being isostructural with Bi24Ge2O40. Starting from Bi2O3 and NiO, orthorhombic Bi2Ni2O5 has also been obtained.

Molecular orbital studies on some 4-substituted pyridine N-oxides and 4-nitroquinoline N-oxide

The electronic structures of a series of 4-substituted pyridine N-oxides and 4-nitroquinoline N-oxide are investigated using the simple Pariser-Parr-Pople (PPP), a modified PPP, IEH and MINDO/2 methods. The electronic absorption band maxima and dipole moments are calculated and compared with experimental values. The photoelectron spectra of these compounds are assigned. The nature of the N-oxide group is characterized using the orbital population distributions. The antifungal activity exhibited by some of these compounds is discussed in terms of the nucleophilic frontier electron densities, superdelocalizabilities and electron acceptor properties. The effect of the electron releasing as well as the electron withdrawing substituents on the physico-chemical properties is explained.

Crystal structure and semiconductor-metal transition of the quasi-two-dimensional transition metal oxide, La2NiO4

Abstract is not available.

Microwave modulation by amorphous-semiconductor switches

Microwave modulation has been achieved by using thin-film amorphous-semiconductor switches made of ternary chalcogenides. X-band microwaves were modulated by a threshold switch at frequencies varying from 100 Hz to 1 MHz, with modulation efficiencies comparable to siliconp¿i¿n diodes. The insertion loss was 0.5 to 0.6 dB and the isolation was 18 dB at 100 mA operating current. Possible applications this method are discussed.

Reaction of thiophosphoryl fluoride with metals and metal oxides

Abstract is not available.

Long-range Coulomb interactions and nanoscale electronic inhomogeneities in correlated oxides

Electronic, magnetic, or structural inhomogeneities ranging in size from nanoscopic to mesoscopic scales seem endemic and are possibly generic to colossal magnetoresistance manganites and other transition metal oxides. They are hence of great current interest and understanding them is of fundamental importance. We show here that an extension, to include long-range Coulomb interactions, of a quantum two-fluid l-b model proposed recently for manganites [Phys. Rev. Lett. 92, 157203 (2004)] leads to an excellent description of such inhomogeneities. In the l-b model two very different kinds of electronic states, one localized and polaronic (l) and the other extended or broad band (b) coexist. For model parameters appropriate to manganites and even within a simple dynamical mean-field theory (DMFT) framework, it describes many of the unusual phenomena seen in manganites, including colossal magnetoresistance (CMR), qualitatively and quantitatively. However, in the absence of long-ranged Coulomb interaction, a system described by such a model would actually phase separate, into macroscopic regions of l and b electrons, respectively. As we show in this paper, in the presence of Coulomb interactions, the macroscopic phase separation gets suppressed and instead nanometer scale regions of polarons interspersed with band electron puddles appear, constituting a kind of quantum Coulomb glass. We characterize the size scales and distribution of the inhomogeneity using computer simulations. For realistic values of the long-range Coulomb interaction parameter V-0, our results for the thresholds for occupancy of the b states are in agreement with, and hence support, the earlier approach mentioned above based on a configuration averaged DMFT treatment which neglects V-0; but the present work has features that cannot be addressed in the DMFT framework. Our work points to an interplay of strong correlations, long-range Coulomb interaction, and dopant ion disorder, all inevitably present in transition metal oxides as the origin of nanoscale inhomogeneities rather than disorder frustrated phase competition as is generally believed. As regards manganites, it argues against explanations for CMR based on disorder frustrated phase separation and for an intrinsic origin of CMR. Based on this, we argue that the observed micrometer (meso) scale inhomogeneities owe their existence to extrinsic causes, e.g., strain due to cracks and defects. We suggest possible experiments to validate our speculation.