Solid state phase equilibria in the PtGaAs system

The PtGaAs solid state equilibrium phase diagram was determined at 600 °C with the use of X-ray powder diffraction, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). No ternary PtGaAs phases were found and limited solid solubility was measured in the constituent binary PtGa and PtAs compounds. GaAs, PtGa and PtAs₂ form a region of three-phase equilibrium which dominates the GaAs side of the phase diagram. The phase diagram is in agreement with previous observations that PtGa and PtAs₂ are the stable phases when platinum thin films are reacted to completion on GaAs.     

New oxyborates in the MgMnBO system

Two new oxyborate compounds were synthesized during a study of the phase relationships between the pinakiolite-ludwigite series of compounds. The structural topologies of these previously unreported materials have been determined experimentally by comparing calculated with observed electron microscope images. Both of these structures are very similar to each other, and also closely related to pinakiolite which consists of flat walls of edge-sharing octahedra connected to zigzag chains of octahedra by triangular BO₃ groups. The two new structures contain similar infinite walls which are separated by slabs of octahedra that are wider than the zigzag chains found in pinakiolite. A new series of structurally related oxyborate compounds can be envisaged and are described.     

First principles search of hard materials within the SiCN ternary system

Starting from C₃N₄ and Si₃N₄ stoichiometries and from the pseudocubic model structure of the former, intermediate phases SiC₂N₄ and Si₂CN₄ are proposed and geometry optimised within density functional built pseudopotential method using both local density (LDA) and generalised gradient approximations (GGA). The ternary compounds are found to be less stable than the two binary systems but the trends in the calculated magnitudes of the bulk moduli B₀ from the fit of the E(V) curves with Birch equation of state: B₀ (SiC₂N₄)=334.5 GPa and B₀ (Si₂CN₄)=270.3 GPa can be interpolated from those of the two extreme compounds: B₀ (C₃N₄)=424.1 GPa and B₀ (Si₃N₄)=219.8 GPa. This translates the chemical role of the substituting element on one hand and allows validating Cohen's semiempirical law relating B₀ to the inverse powers of the average interatomic distances on the other hand. From a mismatch of the chemical bonding in Si(C)NC(Si) chain observed by the electron localisation function (ELF) plot we propose an interpretation for the instability of the intermediate ternary phases. The electronic structure (density of states and band structures) obtained from augmented spherical wave (ASW) calculations of the relaxed structures point to semiconducting behaviour with smaller band gaps for the intermediate phases (∼2 eV, compared with the ∼4 eV gap of binaries).     

Subsolidus phase relationships in the system BaOCaOFe2 O3

The phase relationships at 1100°C among the reaction products of BaO, CaO and Fe₂O₃ were determined by the air quenching technique. Two binary solid solutions are formed, one between barium hexaferrite and a hypothetical calcium tetraferrite and another pseudobinary one adjacent to 2BaO·Fe₂O₃. Based on experimental results obtained by x-ray diffraction, optical microscopy and titrimetric determination of Fe⁺⁴, the 1100°C isothermal section for the system BaOCaOFe₂O₃ was derived.     

Phase diagram for the system Bi2O3CaOSrOCuO in the SrO-rich region

It has been found experimentally that phase diagram for the system Bi₂O₃CaOSrOCuO in SrO-rich region at 850°C in the open air includes three elementary tetrahedra: CaOSrOSr₆Bi₂O₁₁Sr₂CuO₃, CaOSr₂CuO₃Sr₆Bi₂O₁₁Sr_3,5Ca_0,5Bi₂O₇ and Sr₃Bi₂O₆Sr₆Bi₂O₁₁Sr_3,5Ca_0,5Bi₂O₇ Sr₂CuO₃. In the considered interval of corresponding oxide concentrations quaternary oxides are not formed under the above conditions.     

Bubble-point pressures of the H2COCO2 system

Bubble-point pressures of the H₂COCO₂ system were measured at temperatures from 253.15 to 303.15 K and pressures up to 9 MPa. Multiple bubble-points were observed within certain limits of hydrogen compositions. The data have been compared with the calculated results by the Redlich-Kwong and the Peng-Robinson equations of state.     

Reinvestigation of phase relations in the CaOUO2 system

Phase relationships in the binary CaOUO₂ system were reinvestigated. In a carefully controlled reducing atmosphere the formation of binary compounds was not detected and only extensive solid solubility of CaO in UO₂ was observed. In controlled atmosphere in wet hydrogen, a perovskite, Ca₂ (Ca_0.67U⁴⁺_0.33)U⁵⁺O_5.83 is formed as the single binary Ca compound containing uranium in a 4+ valence state.     

Compound and solid-solution formation in the system Li2ONb2O5TiO2

A systematic study of compound and solid-solution formation in the system Li₂ONb₂O₅TiO₂ has been made. Several solid-solution series, based on LiNbO₃, LiNb₃O₈, Li₂Nb₂₈O₇₁, Li₂TiO₃, phase M, Li₂Ti₃O₇, and TiO₂, have been characterized. In all cases, the principal solid-solution mechanism appears to involve stoichiometric formulae with constant overall cation content. One new phase, of approximate formula Li₁₃TiNb₅O₂₁, has been prepared. A subsolidus phase diagram for the ternary system is presented.     

The devitrification of glasses in the binary system SiO2TiO2

The solid solutions series in the system SiO₂TiOP₂ in the vitreous as well as in the devitrified state were investigated by various methods up to 10% by weight TiO₂. The relative intensities of the characteristics infrared absorption bands and of the respective Raman scattering bands about 950 cm⁻¹ reach their maximum at about 4% TiO₂ (by weight).These and other effects observed at this concentration of TiO₂ are discussed in connection with the linking of [SiO₄] and [TiO₄] tetrahedra and with the observed separation of rutile and anatase in small quantities in the devitrification process. A possible sequence of events during the devitrification process in this system is suggested.     

Evidence for the formation of an antase-type VTi oxide solid-state solution

Samples of VTi oxides with V/Ti atomic ratios ranging from 0 to 0.01875 have been prepared by coprecipitation of VOCl₃ and TiCl₄, followed by calcination in air up to 700°C. The samples have been characterized by X-ray diffraction, UV-visible diffuse reflectance, FT-IR and ESR spectroscopy, scanning electron microscopy, and surface area measurements. The results provide evidence for the formation of a well crystallized anatase-type VTi oxide solid-state solution characterized by a small but significant unit cell expansion and by the incorporation of V as a tetravalent species.     

Thermodynamic and sintering studies in the CoWC system

Sintering studies of WC-11%Co samples have been performed in a dilatometer. The temperature dependence of the shrinkage and the shrinkage rate during heating and isothermal treatment has been determined using computer evaluation. The relative magnitude of the densification in the solid and liquid states, respectively, has been determined and correlated to the CoWC phase diagram. Furthermore, some structural changes occurring under decarburizing conditions have been explained. Mechanisms for solid and liquid state sintering are presented.     

Phase equilibria in the ternary system: MgONa2OP2O5: Partial system: Mg3(PO4)2Mg4Na(PO4)3Na4P2O7Mg2P2O7

The partial system Mg₃(PO₄)₂Mg₄Na(PO₄)₃Na₄P₂O₇Mg₂P₂O₇ in the ternary system MgONa₂OP₂O₅ was investigated using thermal and X-ray diffraction analyses and microscopy, and its phase diagram has been determined. In this range of composition, two binary phosphates occur: Mg₄Na(PO₄)₃ and Mg₆Na₈(P₂O₇)₅. The former melts incongruently (at 1155°C) and the latter does congruently (at 808°C). In the partial system of interest, the two sections Mg₄Na(PO₄)₃Mg₂P₂O₇ and Mg₄Na(PO₄)₃Mg₆Na₈(P₂O₇)₅ are studied, and their phase diagrams are established. The partial system is divided into three partial ternary systems in which two ternary eutectics and one ternary peritectic occur.     

Investigation of nonstoichiometry and ferroelectric properties in the ternary system Li2OTa2O5(WO3)2 at 1250°C under atmospheric pressure

X-ray crystallographic studies conducted at atmospheric pressure have allowed determination of the limits of solid solutions with LiTaO₃ structure in the ternary system Li₂OTa₂O₅(WO₃)₂. Stoichiometry analysis has shown that the prevailing type of nonstoichiometry of these phases is simultaneous cationic and anionic deficits. Dielectric measurements carried out on the ceramic samples showed a decrease in the ferroelectric Curie temperature as the composition deviates from that of pure LiTaO₃.     

Phase equilibria of the Ag2OTeO2V2O5 system

The phase diagram Ag₂OV₂O₅TeO₃ is studied in the region rich in TeO₂ with the aid of DTA and X-ray analysis. It is found that the sections TeO₂Ag₂O.V₂O₅.2TeO₂ and Ag₂O.TeO₂Ag₂O.V₂O₅.2TeO₂ are simple ones. A new compound with a composition of Ag₂O.3V₂O₅.6TeO₂ has been found in the section 2TeO₂.V₂O₅Ag₂O.V₂O₅.2TeO₂ which melts incongruently. A part of the liquidus diagram of the system in which the two ternary compounds participate is plotted.