Search Results

You are looking at 11 - 20 of 273 items for :

  • "solid solution" x
  • All content x
Clear All

Abstract  

DTA and XRD methods used to examine the Cr2O3–α-Sb2O4–MoO3 system have shown that a substitution solid solution of MoO3 in CrSbO4 is formed. A study of all the theoretically possible solid solution models has pointed to the fact that Mo6+ ions are incorporated into the CrSbO4 crystal lattice, in the place of Sb5+ ions and the compensation of redundant charges takes place through cation vacancies arising in an Sb5+ sub-lattice. The solubility limit for MoO3 in CrSbO4 does not exceed 25.00 mol%. CrSbO4(s.s.) is stable to ~1320C.

Restricted access

Abstract  

The retention and yields after neutron irradiation under standard conditions by ionizing radiation have been studied as a function of the mole fraction of nitrate in NaIO3–NaNO3 mixed-crystals. The effect of nitrate ion on the retention in solid-solution after irradiation was observed. A probable mechanism is suggested.

Restricted access

Abstract  

Solid solution phases of a formula Fe8V10W16–xMoxO85 where 0≤x≤4, have been obtained, possessing a structure of the compound Fe8V10W16O85. It was found on the base of XRD and DTA investigations that these solution phases melted incongruently, with increasing the value of x, in the temperature range from 1108 (x=0) to 1083 K (x=4) depositing Fe2WO6 and WO3. The increase of the Mo6+ ions content in the crystal lattice of Fe8V10W16O85 causes the lattice parameters a=b contraction with cbeing almost constant. IR spectra of the Fe8V10W16–xMoxO85 solid solution phases have been recorded.

Restricted access

Solid solutions in the MgO-Al2O3-Cr2O3 system

Effects of polymorphism, temperature and pressure

Journal of Thermal Analysis and Calorimetry
Authors: A. Turkin and V. Drebushchak

Abstract  

Coexisting solid solutions with spinel and corundum structure were synthesized at 1773 K and two pressures, 1 bar and 25 kbar. Samples were analyzed by electron microprobe analysis and X-ray powder diffraction. Pressure and temperature were shown to affect the properties of the solid solutions in different ways. Pressure governs the composition of the defect spinel Mg1−xAl2O4, and temperature changes the cation distribution between coexisting phases. This allows one to separate the effects of cation exchange and magnetic contribution to the heat capacity in thermodynamic modeling. The defect spinel itself can form only because γ-Al2O3 exists, polymorph with spinel structure. Thermodynamic considerations argue in favor of eskolaite-spinel assemblages prevailing over corundum-picrochromite ones at very high temperatures deep in the Earth.

Restricted access

Abstract  

Emission Mössbauer (nuclear gamma-resonance) spectra of237Np resulting from the alpha-decay of241Am in solid solutions AmO2–ThO2 and AmO2–UO2 prepared by precipitation from LiF–NaF eutectic melts under fluorine-oxygen exchange were first investigated in the temperature range from 77 to 296 K. The resonant absorbers are NpO2 and NpAl2. The possibility is stated of managing the form of the emission Mössbauer spectra of237Np in dioxides by the directed change of the matrix stoichiometry or by its irradiation by visible light. At temperatures from 77 to 230 K the authors measured for the first time the NGR absorption spectra of237Np in solid solution NpO2–ThO2 with various concentrations of neptunium dioxide. An increase of the absorption line width (approximately by a factor of 4) with a decrease in the NpO2 contents (to 10 mol.%) was explained by the influence of fast electron exchange between Np4+ and Np5+ states observed in the NpO2–ThO2 solid solution at low concentrations of neptunium dioxide.

Restricted access

Abstract  

Two mixtures of pentlandite and the monosulfide solid solution (mss) have been synthesized. The bulk compositions of the samples are Fe6Ni3S8 and Fe3Ni6S8. Differential scanning calorimetry detected exothermic process in the samples under heating. The process takes place in temperature range between phase transition in the mss (near 400 K) and 690 K and is governed by diffusion. X-ray powder diffraction has showed that equilibrium Fe-Ni distribution between pentlandite and the mss is achieved after short-time heating up to 670 K.

Restricted access

band gap of 3.5 eV of ZnS restricts its light absorption to the UV region only. The solid solutions formed between CdS and ZnS have been widely studied and it was found that their band gap energy is tunable by the composition of the solid solution [ 16

Restricted access

Abstract  

Heat capacity of unstable quenched solid solutions (Fe1−xNix)0.96S was measured by DSC (enthalpy method and scanning heating). According to optic microscopy and X-ray powder diffraction, the samples are homogeneous phase of NiAs type with unit cell parameters changing regularly with composition. Heat capacity changes with composition irregularly due to the difference in magnetic properties of the end members: C p/1.96R=4.1 for Fe-rich samples and 3.3 for Ni-rich ones. There is no exact limit between two types of magnetic ordering. Instead, samples with intermediate composition (0.7<x<0.8) show large fluctuations in C p due to the inconsistency of alternative (FeS and NiS) types of magnetic ordering.

Restricted access

Abstract  

It has been shown by the methods of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and infrared spectroscopy (IR) that solid solutions of a formula Cr1−xAlxVMoO7, where x& (0−0.65), are formed in the system CrVMoO7-AlVMoO7. The obtained research results have proven that the ions Al3+ are incorporated into the crystal lattice of CrVMoO7 instead of Cr3+, which causes a contraction of the lattice and a shift of IR absorption bands towards higher values of wavenumbers. The phases Cr1−xAlxVMoO7 melt incongruently in the temperature range from 710C (for x=0.65) to ∼820C in the case of x close to zero

Restricted access

Abstract  

The total conductivity (σT) in bcc γ-Bi2O3 doped with V2O5 system has been measured in the composition range between 1 and 7 mol% V2O5 at different temperatures. Phase transitions for different addition amounts depending on the temperature were investigated by quenching the samples. According to the XRD and DTA/TG results, this bcc type solid solution was stable up to about 720C and the solubility limit was found at ε7 mol% V2O5 in γ-phase. This system showed predominantly an oxide ionic conduction. As the V2O5 addition increased, the ionic conduction increased up to 5 mol% V2O5 at which the highest conductivity was found to be 8.31810-2 Ω-1 cm-1 at 700C and then decreased. It has been proposed that γ-Bi2O3 phase contains a large number of oxide anion vacancies and incorporated vanadium cations at tetrahedral sites which affect the oxygen sublattice of the crystal structure.

Restricted access