Internal Solid State Research Articles

Studies of Indium Tin Oxide-Based Sensing Electrodes in Potentiometric Zirconia Solid Electrolyte Gas Sensors

A zirconia-based potentiometric solid electrolyte gas sensor with internal solid state reference was used to study the response behavior of platinum cermet and indium tin oxide sensing electrodes. Target gases included both oxygen and carbon monoxide in nitrogen-based sample gas mixtures. It was found that with the indium tin oxide sensing electrode, the low-temperature behavior is mainly a result of incomplete equilibration due to contaminations of the electrode surface. On the other hand, some of these contaminant species have been identified as being pivotal for the higher carbon monoxide sensitivity of the indium tin oxide sensing electrode as compared to platinum cermet electrodes.

Crystallization and solid solution attainment of samarium doped ZnO nanorods via a combined ultrasonic-microwave irradiation approach

An advanced sol-gel method is developed via combined ultrasound-microwave irradiation and utilized for the crystallization of pristine and samarium doped zinc oxide nanorods. Organic structure directing agents directed one dimensional growth and air-annealing was applied as post-thermal treatment. Microstructural, optical, and solid state survey was pursued by PXRD, FESEM, TEM, EDS, FTIR, DRS, PL, micro-Raman, H2-TPR, and ESR techniques. Phase analysis by diffraction patterns confirmed the efficacy of irradiation strategy as it improves the crystallinity degree, expedites the hexagonal close pack morphology, and conducts lattice imperfection. Accordingly, aspect ratio and electronic evolution parallel to dopant content is favored. Electron microscopy demonstrated the flake-like rearrangement of nanorods as well as a structure-related growth where a direct proportion exists between atomic packing factor in lattice and aspect ratio. Textural investigation by EDS and FTIR rejected the presence of any impurity verifying an integrated composition. Reflectance and luminescence spectra exhibited characteristic optical behavior with shifts corresponding to dopant concentration. Also, band gap energies increased with samarium addition depicting an opposite trend with respect to unit cell variation. Finally, Raman, TPR, and ESR spectra provided detailed dopant-dependent trends on the internal solid state and defect chemistry of the nanorods. In this regard, maximum shifts in E2high and E1LO phonon modes duly correlated with the vibrations of zinc and oxygen atoms, surface oxygen and bulk ZnO reduction bands, emergence and alteration of samarium centers, along with the dominance of zinc and oxygen vacancies were all resulted due to the utmost lattice imperfection in SZO1.

Amorphous and highly nonstoichiometric titania (TiOx) thin films close to metal-like conductivity

Oxygen-deficient titanium oxide films (TiOx) have been prepared by pulsed laser deposition at room temperature. Samples in their as-deposited state have an average composition of TiO1.6, are optically absorbing and show electronic conductivities in the range of 10 S cm−1. The films are metastable and consist of grains of cubic titanium monoxide (γ-TiO) embedded in an amorphous TiO1.77 matrix. Upon annealing in an argon atmosphere the electrical conductivity of the films increases and comes close to metal-like conductivity (1000 S cm−1) at about 450 °C whereas the local structure is changed: nanocrystalline grains of metallic Ti are formed in the amorphous matrix due to an internal solid state disproportionation. The highly conductive state can be frozen by quenching. During heat treatment in an argon atmosphere a stoichiometric rutile TiO2 surface layer forms due to oxidation by residual oxygen. The combination of a highly conductive TiOx film with such an approximately 20 nm thick rutile cover layer leads to a surprisingly high efficiency for the water-splitting reaction without the application of an external potential.

Internal Solid State Reaction: Formation of Perovskite in NiO‐Matrix

AbstractIsothermal internal reactions of the type A + B = AB taking place in a crystal matrix C are studied experimentally. The matrix crystal C is NiO, A = CaO, B = TiO2 (NiTiO3) and the reaction product AB is the perovskite CaTiO3. Both the morphology of the reaction product and the kinetics of its formation have been investigated and are discussed in the light of a previous theoretical study. In addition, chemical diffusivities of Ca‐ and Ti‐ions in the NiO‐matrix are determined.

Driven internal solid state reactions. A decoration technique

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Internal solid state reactions

Internal solid state reactions in nonmetallic systems (in particular in oxide systems) are reviewed. Firstly, internal oxidations are discussed, both in respect of theory and experiment. Secondly, internal reductions are treated. Thirdly, reactions of type A + B = AB which occur in a solid matrix (γ) are introduced and some pertinent examples are given. Finally, electrochemical internal reactions are analyzed, the characteristics of which are junctions of the type electronic-ionic.

Internal Solid State Reactions

AbstractInternal solid state reactions have first been studied as internal alloy oxidation reactions. The concept of this type of solid state is reactions is generalized and applied to nonmetallic systems. Firstly, interal oxidation reactions with (A,B)O solid solutions are discussed. Then it is shown how one can induce internal reduction reactions with systems such as (A,B)O or (A,B)3O4. A third type of internal solid state reactions is met if A and B diffuse in the solvent crystal C from opposite sides and form a stabel compound AB internally. Finally we discuss AO–BO interdiffusion in in extended solid solutions. It is shown that diffusion potentials can build up which change the local oxygen potential to such an extent that new phases form internally.

Internal Solid State Reactions of the Type A + B = AB: Diffusion‐Controlled Formation of AB from A and B Dissolved in a Crystalline Host Matrix

AbstractA and B diffuse from opposite sides into a finite slice of solid C. After a certain diffusion time the solubility product of a product phase, AB, may be reached and AB precipitates. The location of the first nuclei formation is calculated as a function of the solubilities and the diffusion coefficients of A and B in the matrix C, and of the solubility product. Chemical diffusion coefficients of A and B, which are either constant or proportional to their own concentration, or proportional to the concentration of the other diffusing species are considered. For some sets of typical system parameters the diffusion profiles are calculated and the time and coordinate for first precipitation are shown.—Further growth of small nuclei is given by further diffusion of A and B into the matrix C and to the precipitate, which constitutes a sink for A and B. The precipitate grows in the diffusion field with a preference for certain directions. These directions and the initial growth rate of the precipitate depend on the transport properties of both the matrix and the precipitate, as well as on the thermodynamic conditions of phase coexistence of precipitate and matrix. Limiting cases of an infinitely fast or negligible material transport inside the precipitated phase are considered and the initial growth of a single precipitate in the diffusion field and its shape evolution during growth are calculated.—The global morphology of the assembly of AB precipitates for long diffusion times is discussed by considering the morphological evolution of an intermediate AB layer.

A Novel Kind of Internal Solid State Reactions

A Novel Kind of Internal Solid State Reactions

The origin and diagenesis of cherts from Cyprus

ABSTRACTThe Troodos Massif of Cyprus is overlain by a variety of cherts in pelagic chalks, volcanogenic sediments, radiolarites and radiolarian mudstones, all of Campanian to Upper Eocene age.There are two chert types, granular chert and vitreous chert. X‐ray diffraction (XRD) reveals the silica polymorphs, disordered cristobalite and quartz.Silicification of the chalks varies from incipient, to bedded, granular cherts, all with disordered cristobalite as the main silica phase. Quartzitic cherts are restricted to the base of Upper Palaeocene and Lower Eocene calciturbidite beds. Disordered cristobalite predominates in the radiolarian mudstones at the foot of the sequence.The form of disordered cristobalite in cavities ranges from microspherules of radiating bladed crystals, the ‘lepispheres’ of the Deep Sea Drilling Project (DSDP) to bladed overgrowths, and fibrous silica. In contrast, within the fine grained matrix, the disordered cristobalite takes the form of partly coalescent crude microgranules and microspherules.Most of the chalcedonic quartz in Cyprus is derived by recrystallization of previously inorganically precipitated disordered cristobalite rather than by direct precipitation.According to the concept of impurity‐controlled maturation the composition of host sediment controls the incorporation of exchangeable cations and other impurities into inorganically precipitated disordered cristobalite. With time (up to 100 million years) internal solid state reorganization of the disordered cristobalite is accompanied by gradual expulsion of impurities, until the cristobalite dissolves followed by quartz precipitation. Complete conversion to quartz takes place first in porous calcareous sediments free of impurities, as in the Cyprus calciturbidites; in fine grained clay‐rich sediments, like Cyprus radiolarian mudstones, disordered cristobalite persists much longer. Impurity‐controlled maturation also helps explain the diagenesis of Cyprus chert nodules.