Phase Transition of KNO3 Monitored by Synchrotron X-ray Powder Diffraction

1996 ◽  
Vol 29 (3) ◽  
pp. 265-269 ◽  
Author(s):  
A. Christensen ◽  
P. Norby ◽  
J. C. Hanson ◽  
S. Shimada
Keyword(s):  
Phase Transition ◽  
Cooling Rate ◽  
Powder Diffraction ◽  
Imaging Plate ◽  
Slow Cooling ◽  
X Ray ◽  
Cell Parameters ◽  
Temperature Range ◽  
Temperature Ranges ◽  
Two Phases

The solid-state phase transitions of KNO3 were studied at atmospheric pressure in the temperature range 303 to 533 K by synchrotron X-ray powder diffraction. The detectors used were (i) a curved position-sensitive detector and (ii) a moving imaging-plate system built for time-, temperature- and wavelength-dependent powder diffraction. On heating, the transition from α-KNO3 to β-KNO3 occurs at 401 K. On cooling with a cooling rate of 7 K min−1, the transition from β-KNO3 to γ-KNO3 was observed at 388 K. The phase transition from γ-KNO3 to α-KNO3 occurred at temperatures that strongly depended upon the cooling rate. With a high cooling rate of 15 K min−1 from 403 to 303 K, the γ-KNO3 phase was obtained as a pure phase at 303 K, but it was eventually transformed to α-KNO3 at this temperature, and the phase transition at 303 K was complete within 15 min. With a slow cooling rate of 0.5 K min−1 from 403 to 303 K, the γ-KNO3 phase was formed at 391 K and transformed at 370 K to α-KNO3. With a cooling rate of 7 K min−1 from 403 to 303 K, the γ-KNO3 phase transformed to α-KNO3 in a temperature range between 377 and 353 K. The two phases could exist simultaneously in temperature ranges that were apparently dependent upon the thermal history of the sample. The unit-cell parameters of γ-KNO3 from 383 K to room temperature are reported.

A conformational polymorphic transition in the high-temperature ∊-form of chlorpropamide on cooling: a new ∊′-form

2009 ◽  
Vol 65 (6) ◽  
pp. 770-781 ◽  
Author(s):  
Tatiana N. Drebushchak ◽  
Yury A. Chesalov ◽  
Elena V. Boldyreva
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Structural Changes ◽  
Molecular Conformation ◽  
Polymorphic Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Temperature Range ◽  
Two Phases

Structural changes in the high-temperature ∊-polymorph of chlorpropamide, 4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S, on cooling down to 100 K and on reverse heating were followed by single-crystal X-ray diffraction. At temperatures below 200 K the phase transition into a new polymorph (termed the ∊′-form) has been observed for the first time. The polymorphic transition preserves the space group Pna21, is reversible and is accompanied by discontinuous changes in the cell volume and parameters, resulting from changes in molecular conformation. As shown by IR spectroscopy and X-ray powder diffraction, the phase transition in a powder sample is inhomogeneous throughout the bulk, and the two phases co-exist in a wide temperature range. The cell parameters and the molecular conformation in the new polymorph are close to those in the previously known α-polymorph, but the packing of the z-shaped molecular ribbons linked by hydrogen bonds inherits that of the ∊-form and is different from the packing in the α-polymorph. A structural study of the α-polymorph in the same temperature range has revealed no phase transitions.

Barium hollandite-type compounds BaxFe2xTi8−2xO16 with x=1.143 and 1.333

1999 ◽  
Vol 14 (1) ◽  
pp. 31-35 ◽  
Author(s):  
J. M. Loezos ◽  
T. A. Vanderah ◽  
A. R. Drews
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Framework Structure ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Acta Crystallogr

Experimental X-ray powder diffraction patterns and refined unit cell parameters for two barium hollandite-type compounds, BaxFe2xTi8−2xO16, with x=1.143 and 1.333, are reported here. Compared to the tetragonal parent structure, both compounds exhibit monoclinic distortions that increase with Ba content [Ba1.333Fe2.666Ti5.334O16: a=10.2328(8), b=2.9777(4), c=9.899(1) Å, β=91.04(1)°, V=301.58(5) Å3, Z=1, ρcalc=4.64 g/cc; Ba1.143Fe2.286Ti5.714O16: a=10.1066(6), b=2.9690(3), c=10.064(2) Å, β=90.077(6)°, V=301.98(4) Å3, Z=1, ρcalc=4.48 g/cc]. The X-ray powder patterns for both phases contain a number of broad, weak superlattice peaks attributed to ordering of the Ba2+ ions within the tunnels of the hollandite framework structure. According to the criteria developed by Cheary and Squadrito [Acta Crystallogr. B 45, 205 (1989)], the observed positions of the (0k1)/(1k0) superlattice peaks are consistent with the nominal x-values of both compounds, and the k values calculated from the corresponding d-spacings suggest that the Ba ordering within the tunnels is commensurate for x=1.333 and incommensurate for x=1.143. High-temperature X-ray diffraction data indicate that the x=1.333 compound undergoes a monoclinic→tetragonal phase transition between 310 and 360 °C.

scholarly journals Single-crystal X-ray and neutron powder diffraction investigation of the phase transition in tetrachlorobenzene

2006 ◽  
Vol 62 (2) ◽  
pp. 287-295 ◽  
Author(s):  
Sarah A. Barnett ◽  
Charlotte K. Broder ◽  
Kenneth Shankland ◽  
William I. F. David ◽  
Richard M. Ibberson ◽  
...  
Keyword(s):  
Phase Transition ◽  
Single Crystal ◽  
Powder Diffraction ◽  
Structural Changes ◽  
Neutron Powder Diffraction ◽  
X Ray Diffraction ◽  
Polymorphic Phase Transition ◽  
X Ray ◽  
Apparent Loss ◽  
Two Phases

The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. The diffraction experiments show a reversible phase change that occurs as a function of temperature with no apparent loss of sample quality on transition between the two phases. Neutron powder diffraction gives detailed information on the molecular structural changes and lattice parameters from 2 K to room temperature. The structure of the low-temperature form has been elucidated for the first time using single-crystal X-ray diffraction. Comparison of the α and β structures show that they are both based on the same sheet motif, with the differences between the two being very subtle, except in terms of crystal symmetry. Detailed analysis of the structures revealed the changes required for inter-conversion. A computational polymorph search showed that these two sheet structures are more thermodynamically stable than alternative herringbone-type structures.

Neutron and X-Ray Diffraction Studies of Piezoelectric Materials under Non-Ambient Conditions

2004 ◽  
Vol 443-444 ◽  
pp. 277-282
Author(s):  
J. Haines ◽  
O. Cambon ◽  
J. Rouquette ◽  
V. Bornand ◽  
Ph. Papet ◽  
...  
Keyword(s):  
Phase Transition ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Piezoelectric Materials ◽  
Germanium Dioxide ◽  
Raman Signal ◽  
Imaging Plate ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase

In depth study of the crystal structures of piezoelectric materials as a function of temperature, pressure and composition allows for the design and optimization of such materials and defines the conditions of their use in technological applications. Results from studies on two classes of piezoelectric materials are described, the α-quartz group and the ferroelectric perovskite group. The structures of α-quartz-type germanium dioxide and iron phosphate were refined at high temperatures by the Rietveld method using time-of-flight neutron powder diffraction data. The α-β phase transition occurs at 980 K in FePO4, whereas for GeO2, no β phase is observed. The intertetrahedral bridging angle θ and the tilt angle δ in GeO2exhibit thermal stabilities that are significantly greater than α-quartz. The temperature dependence of these angles is found to be a function of the initial structural distortion in α-quartz homeotypes with the notable exception of α-quartz-type FePO4, which appears to be dynamically unstable. The stability of α-quartz and α-quartz-type germanium dioxide was investigated at high pressure by x-ray powder diffraction. New six-fold coordinated forms were found in both materials. The important, perovskite-type, piezoelectric material PbZr0.52Ti0.48O3was studied up to 18 GPa by angle-dispersive, x-ray diffraction using an imaging plate and by Raman spectroscopy. A novel phase transition was found in this system at close to 5 GPa. Whereas the x-ray diffraction data indicated no deviation from cubic symmetry above this pressure, a strong Raman signal was present in this phase, which is similar to those observed for ferroelectric relaxors.

X-Ray Diffraction Investigation of BeO Calcination Processes

1960 ◽  
Vol 4 ◽  
pp. 19-39 ◽  
Author(s):  
R.C. Rau
Keyword(s):  
Direct Conversion ◽  
Theoretical Density ◽  
X Ray Diffraction ◽  
Slow Cooling ◽  
Transformation Temperatures ◽  
X Ray ◽  
Structure Information ◽  
Temperature Range ◽  
Intermediate Phases ◽  
Temperature Ranges

AbstractTo aid in the study of the preparation and properties at BeO, X-ray diffraction investigations were performed to determine the various phases and transformation temperatures occurring in the different BeO calcination processes and to determine the theoretical density of the final BeO product.The hydroxide, sulfate, and oxalate of beryllium were the starting materials in the three calcination series. The samples studied were prepared by heating small portions of the starting materials for 1 hr at various temperatures and slow cooling. Analysis of the hydroxide series showed a direct conversion from Be(OH)a to BeO by simple loss of water. However, both the sulfate series and the oxalate series go through a series of intermediate phases in transforming to BeO. X-ray data and structure information have been obtained for most of these phases, and temperature ranges of their occurrence have been established.Wherever possible, the X-ray results have been compared with results of stereoscopic and polarizing microscope examinations, and temperature range of occurrence have been compared with thermal balance curves.

Concomitant cocrystal and salt: no interconversion in the solid state

2019 ◽  
Vol 75 (3) ◽  
pp. 313-319
Author(s):  
Evgeniy A. Losev ◽  
Elena Boldyreva
Keyword(s):  
Phase Transition ◽  
Chemical Composition ◽  
Solid State ◽  
X Ray Diffraction ◽  
Melting Points ◽  
Polymorphic Transitions ◽  
X Ray ◽  
Temperature Range ◽  
Two Phases ◽  
Molecular Salt

A cocrystal and a molecular salt of β-alanine and DL-tartaric acid, C3H8NO2 +·C4H4O6 −, of the same chemical composition, were studied over a wide temperature range by single-crystal and powder X-ray diffraction. Neither the interconversion between the two phases nor any polymorphic transitions were observed in the temperature range from 100 K to the melting points. This contrasts with the solvent-mediated phase transition from the salt to the cocrystal in a slurry that has been documented earlier.

Distinguishing among schoepite, [(UO2)8O2(OH)12](H2O)12, and related minerals by X-ray powder diffraction

1997 ◽  
Vol 12 (4) ◽  
pp. 230-238 ◽  
Author(s):  
Robert J. Finch ◽  
Frank C. Hawthorne ◽  
Mark L. Miller ◽  
Rodney C. Ewing
Keyword(s):  
Powder Diffraction ◽  
Unit Cell ◽  
Powder Diffraction File ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Fine Grained ◽  
Fine Grained Material ◽  
Two Phases ◽  
Atomic Parameters

We have calculated X-ray powder-diffraction data for schoepite, [(UO2)8O2(OH)12](H2O)12, using unit-cell and atomic parameters from the crystal structure (a14.337,b16.813,c14.781,Z=4,Dx=4.87gcm−3). Schoepite crystallizes in space groupP21cabut is strongly pseudo- centrosymmetric, and observed reflections (Irel>0.1%) conform to space groupPbca. The six strongest reflections for schoepite are [d(Å),hkl(relative intensity)] 7.365,002(100), 3.253,242(55), 3.626,240(36), 3.223,402(25), 3.683,004(20), 2.584,244(18). The calculated intensities of reflections that distinguish space groupPbcafrom space groupPbna(the space group of metaschoepite), i.e.,h0lwithhodd andleven, are weak, and may not be evident in experimental powder patterns. Theaaxis of schoepite (14.34 Å) is significantly longer than that of synthetic metaschoepite (13.98 Å), and the two phases can best be distinguished by their unit-cell parameters. However, potential overlap of the strongest reflections can make identification and unit-cell determination difficult, especially for fine-grained material. Natural samples commonly contain intergrowths of schoepite, metaschoepite, and dehydrated schoepite. The calculated powder pattern for schoepite agrees well with data reported for natural schoepite (PDF 13-241) but shows discrepancies with the data from synthesis products. Data for “synthetic schoepite” indicate that this product was a mixture. Powder data labeled “paraschoepite” in the Powder Diffraction File do not correspond to the mineral of that name.

scholarly journals Monitoring protein precipitates by in-house X-ray powder diffraction

2013 ◽  
Vol 28 (S2) ◽  
pp. S458-S469 ◽  
Author(s):  
Kenny Ståhl ◽  
Christian G. Frankær ◽  
Jakob Petersen ◽  
Pernille Harris
Keyword(s):  
Powder Diffraction ◽  
Protein Crystal ◽  
Data Sets ◽  
Crystal Forms ◽  
X Ray ◽  
Cell Parameters ◽  
X Ray Scattering ◽  
Source Organism ◽  
Peak Asymmetry ◽  
Overlapping Peaks

Powder diffraction from protein powders using in-house diffractometers is an effective tool for identification and monitoring of protein crystal forms and artifacts. As an alternative to conventional powder diffractometers a single crystal diffractometer equipped with an X-ray micro-source can be used to collect powder patterns from 1 µl samples. Using a small-angle X-ray scattering (SAXS) camera it is possible to collect data within minutes. A streamlined program has been developed for the calculation of powder patterns from pdb-coordinates, and includes correction for bulk-solvent. A number of such calculated powder patterns from insulin and lysozyme have been included in the powder diffraction database and successfully used for search-match identification. However, the fit could be much improved if peak asymmetry and multiple bulk-solvent corrections were included. When including a large number of protein data sets in the database some problems can be foreseen due to the large number of overlapping peaks in the low-angle region, and small differences in unit cell parameters between pdb-data and powder data. It is suggested that protein entries are supplied with more searchable keywords as protein name, protein type, molecular weight, source organism etc. in order to limit possible hits.

Heklaite, KNaSiF6, a new fumarolic mineral from Hekla volcano, Iceland

2010 ◽  
Vol 74 (1) ◽  
pp. 147-157 ◽  
Author(s):  
A. Garavelli ◽  
T. Balić-Žunić ◽  
D. Mitolo ◽  
P. Acquafredda ◽  
E. Leonardsen ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Quantitative Chemical Analysis ◽  
Unit Cell Parameters ◽  
Orthorhombic Space Group ◽  
Synthetic Compound ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
Fine Grained ◽  
The Ideal

AbstractHeklaite, with the ideal formula KNaSiF6, was found among fumarolic encrustations collected in 1992 on the Hekla volcano, Iceland. Heklaite forms a fine-grained mass of micron- to sub-micron-sized crystals intimately associated with malladrite, hieratite and ralstonite. The mineral is colourless, transparent, non-fluorescent, has a vitreous lustre and a white streak. The calculated density is 2.69 g cm–3. An SEM-EDS quantitative chemical analysis shows the following range of concentrations (wt.%): Na 11.61–12.74 (average 11.98), K 17.02–18.97 (average 18.29), Si 13.48 –14.17 (average 13.91), F 54.88–56.19 (average 55.66). The empirical chemical formula, calculated on the basis of 9 a.p.f.u., is Na1.07K0.96Si1.01F5.97. X-ray powder diffraction indicates that heklaite is orthorhombic, space group Pnma, with the following unit-cell parameters: a = 9.3387(7) Å, b = 5.5032(4) Å, c = 9.7957(8) Å , V = 503.43(7) Å3, Z = 4. The eight strongest reflections in the powder diffraction pattern [d in Å (I/I0) (hkl)] are: 4.33 (53) (102); 4.26 (56) (111); 3.40 (49) (112); 3.37 (47) (202); 3.34 (100) (211); 2.251 (27) (303); 2.050 (52) (123); 2.016 (29) (321). On the basis of chemical analyses and X-ray data, heklaite corresponds to the synthetic compound KNaSiF6. The name is for the type locality, the Hekla volcano, Iceland.

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