High-temperature X-ray Powder Research Articles

Synthesis, thermal analysis, IR spectrum and crystal structure of K2Th2(NO3)10·15H2O. Structural evolution of thorium nitrate complexes

The compound K2Th2(NO3)10·15H2O was synthesized, and its crystal structure was determined by X-ray diffraction analysis: space group P1¯; a=10.3068(9), b=13.1642(11), c=13.9605(12)Å, α=95.276(2)°, β=90.425(2), γ=92.749(2)°, Z=2; R=0.0379. Thermal conditions of decomposition of the compound are studied by differential scanning calorimetry and high-temperature X-ray powder. The compound was studied by IR spectroscopy and was assigned bands.

In situ high-temperature X-ray diffraction and spectroscopic study of fibroferrite, FeOH(SO4)·5H2O

The thermal dehydration process of fibroferrite, FeOH(SO4)·5H2O, a secondary iron-bearing hydrous sulfate, was investigated by in situ high-temperature synchrotron X-ray powder diffraction (HT-XRPD), in situ high-temperature Fourier transform infrared spectroscopy (HT-FTIR) and thermal analysis (TGA-DTA) combined with evolved gas mass spectrometry. The data analysis allowed the determination of the stability fields and the reaction paths for this mineral as well as characterization of its high-temperature products. Five main endothermic peaks are observed in the DTA curve collected from room T up to 800 °C. Mass spectrometry of gases evolved during thermogravimetric analysis confirms that the first four mass loss steps are due to water emission, while the fifth is due to a dehydroxylation process; the final step is due to the decomposition of the remaining sulfate ion. The temperature behavior of the different phases occurring during the heating process was analyzed, and the induced structural changes are discussed. In particular, the crystal structure of a new phase, FeOH(SO4)·4H2O, appearing at about 80 °C due to release of one interstitial H2O molecule, was solved by ab initio real-space and reciprocal-space methods. This study contributes to further understanding of the dehydration mechanism and thermal stability of secondary sulfate minerals.

Order–disorder phase transition in the antiperovskite-type structure of synthetic kogarkoite, Na3SO4F

High-temperature phase transition of synthetic kogarkoite, Na3SO4F, has been studied by high-temperature X-ray powder and single-crystal diffraction. The temperature of the phase transition can be estimated as 112.5±12.5°C. The low-temperature phase, α-Na3SO4F, at 293K, is monoclinic, P21/m, a=18.065(3), b=6.958(1), c=11.446(1)Å, β=107.711(1)°, Z=12. The structure contains thirteen symmetrically independent Na sites with coordination numbers varying from 6 to 8, and six independent S sites. The high-temperature β-phase at 423K is rhombohedral, R-3m, a=6.94(1), c=24.58(4)Å, Z=9. The crystal structure of both polymorphs of Na3SO4F can be described as a 9R antiperovskite polytype based upon triplets of face-sharing [FNa6] octahedra linked into a three-dimensional framework by sharing corners. In the α-modification, the SO4 tetrahedra are completely ordered and located in the framework cavities. In the β-modification, there are only two symmetrically independent Na atoms in the structure. The main difference between the structures of the α- and β-phases is the degree of ordering of the SO4 tetrahedra: in the α-modification, they are completely ordered, whereas, in the β-modification, the complete disorder is observed, which is manifested in a number of low-occupied O sites around fully occupied S sites. The phase transition is therefore has an order–disorder character and is associated with the decrease of structural complexity measured as an information content per unit cell [577.528 bits for the low- (α) and 154.830 bits for the high- (β) temperature modifications].

Regeneration of high-silica zeolites after sulfamethoxazole antibiotic adsorption: a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study

AbstractThe thermal regeneration of sulfamethoxazole (SMX)-loaded Y and ZSM-5 zeolites was studied using a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study. The evolution of the structural features was monitored in real time in the 30–575°C temperature range by full-profile Rietveld analysis. SMX thermal degradation pathways into high-silica zeolite antibiotic adducts, as well as the release of evolved species are similar to those for pure SMX. The adsorption/desorption process occurs without any significant loss of zeolite crystallinity, though slight deformations to the channel apertures are observed. Regenerated zeolites regain almost perfectly ‘bare’ (i.e. unloaded) material unit-cell parameters and only a slight memory effect, in terms of structural deformations induced by the process, is registered in the channel geometry. Interestingly, these changes do not affect the adsorption properties of the regenerated samples, which are able to re-adsorb comparable amounts of antibiotic molecules as in the first adsorption cycle.

Application of High Temperature Quantitative X-Ray Powder Diffraction on Determination of Ternary System

This paper has put forward a high-temperature quantitative X-ray powder diffraction analysis method for the determination of an isothermal section of a ternary system in comparison with a conventional method. In a three-phase region of the isothermal section at 1150 °C of Cu2O(CuO)-Al2O3-SiO2 pseudo-ternary system, the compositions of the solid phase points of three system points are determined according to the quantitative analysis of the crystalline phases in the samples carried out by Rietveld method. Then the liquid phase point of the three-phase region is determined according to the crosspoints of the tie lines of every pair of system point and solid phase point. The precisions of the analytical results have reached to be 0.1 ~ 5.0 %. By comparison, a good result is obtained for the determination of the liquid phase point of the three-phase region in the isothermal section at 1150 °C when the analytical results of high-temperature RQA analysis are used in determination of the isothermal section of the pseudo-ternary system.

Volume collapse inLaMnO3at the Jahn-Teller transition temperature

We have studied the volume collapse of ${\mathrm{LaMnO}}_{3}$ at the Jahn-Teller (JT) transition temperature ${T}_{\mathrm{JT}}=750\mathrm{K}$ which has recently been found in high-temperature powder x-ray and neutron diffraction experiments. We construct a model Hamiltonian involving the pseudospin of ${\mathrm{Mn}}^{3+}$ ${e}_{g}$ states, the staggered JT distortion and the volume strain coordinate. We show that the anharmonic coupling between these primary and secondary order parameters leads to the first-order JT phase transition associated with a comparatively large reduction of the unit cell volume of $\ensuremath{\Delta}V/V\ensuremath{\simeq}{10}^{\ensuremath{-}2}.$ We explain the temperature dependence of JT distortions and volume strain and discuss the volume change as function of the anharmonic coupling constant. A continuous change to a second-order transition as function of model parameters is obtained. This behavior is also observed under Ba doping.

High Temperature X-Ray and Neutron Powder Diffraction Study of a Phase Transition in Copper Hydroxide Nitrate

High Temperature X-Ray and Neutron Powder Diffraction Study of a Phase Transition in Copper Hydroxide Nitrate