A. Yu. Zavrazhnov

T - x Phase Diagram of the In-S System

The T-x phase diagram of the In-S system has been studied by differential thermal analysis and x-ray diffraction between 300 and 1150°C. The compounds identified in this temperature range are InS, In6S7, In3S4, and In2S3. We have determined the temperatures of the monotectic equilibrium L1(In) + InS = L2; peritectic equilibria involving InS, In6S7, and In3S4; and polymorphic transformations of InS and In2S3. Our results demonstrate that raising the cooling rate to a certain level leads to a sharp transition from near-equilibrium to metastable phase relations in the In-S system.

Chemical transport reactions as a new variant of the phase composition control

It is shown that the composition of low-volatility two-component compounds in the Ga-Se system can be controlled using chemical transport reactions (CTR). For long-term heat treatment of a low-volatility phase in the presence of a transport agent, the annealed phase composition was found to be determined only by the temperature conditions and the chemical nature of the sample. In the case of a two-temperature anneal of gallium selenides with added iodine, the sample stability domains are presented as a function of the cold and hot zones temperatures. The role of the transport agent is discussed. The possibility of applying this technique to other binary systems with low-volatility phases is also considered.

Metastable states in inorganic systems

Changes in inorganic systems associated with the formation of metastable states and their relaxation are considered using supramolecular theory of eutectics. After analysis of the existing theories and concepts describing possible transition mechanisms of nonequilibrium amorphous structures to a crystalline state, the conclusion that there is poor correspondence of experimental data to those theories is made. Owing to the complexity of relaxation processes, it was proposed to divide the objects of investigation into groups considering the different interaction potentials and size parameters of substructures. Inorganic binary eutectic systems were classified as a special group. The peculiarities of the relaxation processes in quenched non-autonomous phases are shown in a few examples with consideration of characteristic temperatures and time.

Refinement of the In-S phase diagram using spectrophotometric characterization of equilibria between hydrogen and indium sulfides

A spectrophotometric procedure for hydrogen sulfide determination has been developed and utilized to study the phase diagram of the In-S system using hydrogen as an auxiliary component. Elemental analysis of the hydrogen-containing vapor phase allows the principal thermodynamic properties of the indium sulfides in equilibrium with the vapor phase to be assessed in wide temperature and composition ranges. Our results confirm the existence of a narrow two-phase field between In3−xS4 and In2S′3 (low-temperature phase), which is bounded from above by the peritectic decomposition temperature of (about 415°C). We have determined the temperature-dependent sulfur (S2) vapor pressure over condensed indium sulfides. For the equilibria studied in greatest detail, the present results correlate well with mass spectrometry data for indium sulfides.

Solid-State Reactions in CdS–Bi2S3 Thin Films

Structural, electrical, and optical data are used to elucidate the mechanisms of solid-state reactions in thin CdS–Bi2S3 films prepared by spray pyrolysis. The results indicate the formation of substitutional solid solutions and a chemical compound and intercalation of Cd between layers of Bi2S3 .

Nonadditivity of Properties and the Possibility of Formation of Ensembles of Incommensurate Structures in the GaSe–Ga2Se3 System

The GaSe–Ga2Se3 system is studied by x-ray diffraction, electron microscopy, and differential scanning calorimetry. The results demonstrate that the nonadditivity of heat capacity observed near the eutectic composition after quenching is similar to the nonadditivity of properties in misfit layer compounds, which contain incommensurate structural components. The origin of this similarity is discussed in terms of the self-organization of interacting incommensurate elements in the melt and the formation of unstable suprastructural ensembles.

Phase transformations of indium mono- and sesquisulfides studied by a novel static thermal analysis technique

This paper analyzes some features of the indium-sulfur system studied by differential thermal analysis and a novel, specially developed, static technique: chromatothermography. The technique builds on imaging of the surface of the substance of interest, whose temperature is varied stepwise, with isothermal holds. We describe algorithms for processing such images with the aim of gaining information about phase transition temperatures of the substance. The present results demonstrate that the high-temperature phase of indium monosulfide (InS) exists in a narrow temperature range (≃30 K). The phases In3 − xS4 (spinel) and In2S3 (low-temperature, tetragonal phase), very similar in stoichiometry, are indeed separated by a narrow heterogeneous region. In2S3 peritectically decomposes at a temperature near 410°C to form In3 − xS4 and a sulfur-based melt.

Selective chemical vapor transport as a means of varying the composition of nonstoichiometric indium sulfides

Investigation of halide vapor transport with the participation of indium and indium sulfides in a closed system indicates that applying a temperature gradient is insufficient for quantitative spontaneous indium transfer from the lower indium sulfides or for the transport of elemental indium. A major reason for this is that the vapor phase over indium and its lower sulfides is dominated by monohalides. Impossible under conventional experimental conditions, chemical vapor transport can be achieved by diluting indium with an inert substance, e.g., gold. Our results indicate that the vapor transport of indium is possible in systems of the form indium sulfide-indium chloride vapor-charge (Au-In) and that chloride vapor transport can be used to nondestructively control the composition of indium sulfides. The transport process is shown to be selective and reversible. Conditions are determined for nondestructive chemical transport control over the composition of indium sulfides.

Chemical Vapor Transport: A Viable Approach to Controlling the Composition of Intermetallic Phases Promising for Catalyst Engineering

A “dry” process is described for preparing activated metals via removal of the active component from an intermetallic phase using selective chemical vapor transport. In closed vapor transport systems containing the intermetallic phases NixGa1 − x and CuxGa1 − x, gallium transport leads to the development of steady states, and the composition of the intermetallic phase is determined by the sample and charge temperatures. To produce catalytically active materials, the active component should be removed under more nonequilibrium conditions, e.g., in flowing transport agent vapor. For nickel-based structures, the catalytic activity of substances prepared by a conventional process has been compared to that of substances synthesized using selective chemical vapor transport.

Oxidizing Intercalation of Layered Structures

5. I. Hasegawa, T.Na kamura, S. Motojirna, and M. Kajiwara, J. Mater. Chern. 5, 193 (1995). 6. I. Hasegawa, T.Nakamura, S. Motojima, and M. Kajiwara, J. Sol-Ge l Sci. Techno!. 8, 577 (1997). 7. I. Hasegawa, T. Nakamura, and M. Kajiwara, Mater. Res. Bul!. 3 1, 869 (1996). 8. I. Hasegawa, Y. Fukud a, and M. Kajiwara, J. Eur, Ce ram. Soc. 17 , 1467 (1997) . 9. I. Hasegawa, Y. Fukuda , and M. Kajiwara, Ceram. Int er. 25,523 (1999). 10. A. Hendry and K.H. Jack in Special Ceramics 6, edi ted by P. Popper, (British Cera mics Research Association , Stoke-on-trent, 1975), p. 199.