scholarly journals T-induced displacive phase transition of end-member Pb-lawsonite

2016 ◽  
Vol 80 (2) ◽  
pp. 249-267 ◽  
Author(s):  
Martin Ende ◽  
Bernd Wunder ◽  
Monika Koch-Müller ◽  
Thoma. Pippinger ◽  
Gernot Buth ◽  
...  
Keyword(s):  
Phase Transition ◽  
Principal Component ◽  
Hierarchical Cluster ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
Raman Spectroscopic ◽  
Piston Cylinder ◽  
Displacive Phase Transition ◽  
Structural Environment ◽  
Xrd Patterns

AbstractPb-lawsonite, PbAl2[(OH)2|Si2O7]·H2O, space group Pbnm, was synthesized as crystals up to 15 μm × 5 μm × 5 μm in size by a piston cylinder technique at a pressure of ∼4 GPa and a temperature of 873 ± 10 K. Temperature-dependent powder and single-crystal X-ray diffraction (XRD) analyses partly using synchrotron radiation as well as Raman spectroscopic investigations reveal a phase transition around 445 K resulting in the Cmcm high-temperature structure. The transformation temperature is considerably higher than that of lawsonite around 273 K, which is characterized predominantly by proton order/disorder. The transition is confirmed using principal component analysis and subsequent hierarchical cluster analysis on both the powder XRD patterns and the Raman spectra. Furthermore, a non-uniform change is observed around 355 K, which is not as pronounced as the 445 K transition and apparently comes from enhanced hydrogen bonding, which stops the atom shifts in Pb-lawsonite. These are the same bonds that mainly characterize the phase transition in lawsonite around 273 K. In contrast, the structural transition of Pblawsonite at 445 K seems to originate from the interaction of the SiO4tetrahedra and AlO6octahedra framework with the Pb2+cation. The structural environment of Pb2+can be described by a 12-fold coordination above 445 K, which changes towards irregular ten-fold coordination below this temperature. An assignment of the O–H stretching Raman bands confirms moderately strong H bonds in Pb-lawsonite, whereas both strong and weak H bonds exist in lawsonite. Therefore, a further phase transition of Pblawsonite, similar to that of lawsonite around 273 K, is not expected.

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites

2001 ◽  
Vol 57 (3) ◽  
pp. 221-230 ◽  
Author(s):  
A. Guelylah ◽  
G. Madariaga ◽  
V. Petricek ◽  
T. Breczewski ◽  
M. I. Aroyo ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Mode Analysis ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
New Type ◽  
Low Temperature Phase

The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100–300 K. Using DSC measurements, a phase transition has been detected at 213 K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690 (8), b = 20.136 (2), c = 10.0329 (4) Å, γ = 90.01 (1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds.

X-ray diffraction study revealing phase coexistence in barium titanate stannate

2004 ◽  
Vol 19 (10) ◽  
pp. 2834-2840 ◽  
Author(s):  
Volkmar Mueller ◽  
Horst Beige ◽  
Hans-Peter Abicht ◽  
Christian Eisenschmidt
Keyword(s):  
Phase Transition ◽  
Ferroelectric Phase ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray ◽  
Temperature Range ◽  
Xrd Study ◽  
Xrd Patterns ◽  
Tetragonal Phase Transition

In this paper, the results of a temperature dependent x-ray diffraction (XRD) study on BaTi0.95Sn0.05O3 (BTS-5) ceramics are compared with dielectric measurements. The orthorhombic-tetragonal phase transition at T2 = 306 K is found to proceed in a considerably wider temperature range than expected from the dielectric anomaly. Although the macroscopic properties of BTS-5 indicate a rather sharp ferroelectric phase transition at Tc = 358K, we observe anomalous XRD-patterns in a 25 K wide temperature range. This is interpreted in terms of mechanically clamped tetragonal and cubic phase, coexisting in the vicinity of Tc in grains with inhomogeneous Sn-distribution.

Phase Transition and Thermochromism of the Hybrid (C12H25NH3)2FeCl4

2006 ◽  
Vol 111 ◽  
pp. 55-58
Author(s):  
L.L. Guo ◽  
Y.D. Dai ◽  
H.X. Liu ◽  
Shi Xi Ouyang
Keyword(s):  
Phase Transition ◽  
Structural Changes ◽  
Energy Transition ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Thermal Gravimetry ◽  
Reversible Phase Transition ◽  
Rotational Motions ◽  
Xrd Patterns ◽  
Reversible Phase

This paper focuses on the structural change and the thermochromism of the phase transition of the hybrid (C12H25NH3)2FeCl4. The temperature and the structures of the phase transition is investigated by a thermal gravimetry (TG) and differential scanning calorimetry (DSC), an infrared spectra (IR) and X-ray diffraction (XRD) patterns. The UV adsorption spectra account for the thermochromism. The results suggest that the reversible phase transition arises from the structural changes of the organic chains. The thermochromism is presumably due to the electrons redistribution on the levels and to the energy transition to translational and rotational motions of the organic chains.

scholarly journals Temperature variable high-pressure volumetric studies of diethylene glycol

2014 ◽  
Vol 70 (a1) ◽  
pp. C268-C268 ◽  
Author(s):  
Kamil Dziubek ◽  
Mohamed Mahgoub ◽  
Hesham Alsoghier ◽  
Andrzej Katrusiak
Keyword(s):  
Phase Transition ◽  
Diethylene Glycol ◽  
Volume Data ◽  
X Ray Diffraction ◽  
X Ray ◽  
Piston Cylinder ◽  
Hot Air ◽  
Phase Transition Pressure ◽  
Thermodynamic Conditions ◽  
Temperature Variable

It was demonstrated that direct compression experiments in a piston-cylinder press provide precise information on volume data and phase transition pressure complementary to X-ray diffraction. The experimental setup, described in detail previously [1], is capable of compressing liquid and solid samples up to ca. 2 GPa. We have continued these studies adding temperature control of the sample. Piston and cylinder chamber was placed in an thermally isolated mantle. The constant temperature was maintained by circulating hot air. As demonstrated by the experiments on diethylene glycol, it is a relatively quick and simple, yet efficient method for exploring phase diagrams and recording volume reduction at phase transition in different thermodynamic conditions.

X-Ray Diffraction Study of the Phase Transition of the ${\rm Si}(111)(\sqrt{3} \times \sqrt{3})\mbox{-Ag}$ Surface

2003 ◽  
Vol 10 (02n03) ◽  
pp. 519-524 ◽  
Author(s):  
Toshio Takahashi ◽  
Hiroo Tajiri ◽  
Kazushi Sumitani ◽  
Koichi Akimoto ◽  
Hiroshi Sugiyama ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Low Temperatures ◽  
Diffuse Scattering ◽  
Room Temperature ◽  
Bragg Reflection ◽  
Grazing Incidence ◽  
X Ray Diffraction ◽  
X Ray ◽  
Displacive Phase Transition

The structure of the [Formula: see text] surface was studied at both room temperature and a low temperature of 50 K using grazing incidence X-ray diffraction. At low temperatures diffuse scattering was observed in addition to Bragg reflection. Least squares analyses for Bragg reflections using anisotropic Debye–Waller factors show that the structure at 50 K is consistent with an inequivalent triangle (IET) model, while the structure at room temperature is explained by a honeycomb-chained triangle (HCT) model with strong anisotropic Debye–Waller factors. From the temperature dependence of diffuse scattering, the phase transition temperature Tc and critical exponent β were determined to be about 150 K and 0.27. Some Bragg intensities showed discontinuous changes in their first derivatives at Tc. The results favor a displacive phase transition rather than an order–disorder one.

Structural and Raman spectroscopic studies of the two M0.50SbFe(PO4)3 (M = Mg, Ni) NASICON phases

2017 ◽  
Vol 32 (S1) ◽  
pp. S40-S51
Author(s):  
Abderrahim Aatiq ◽  
Asmaa Marchoud ◽  
Hajar Bellefqih ◽  
My Rachid Tigha
Keyword(s):  
Room Temperature ◽  
Structural Information ◽  
Rietveld Analysis ◽  
Spectroscopic Studies ◽  
X Ray Diffraction ◽  
X Ray ◽  
Raman Spectroscopic ◽  
Raman Spectroscopic Study ◽  
Unit Cells ◽  
Xrd Patterns

Structures of the two M0.50SbFe(PO4)3 (M = Mg, Ni) phases, abbreviated as [Mg0.50] and [Ni0.50], were determined at room temperature from X-ray diffraction (XRD) powder data using the Rietveld analysis. Both compounds belong to the NASICON structural family. XRD patterns of [Mg0.50] and [Ni0.50] phases were easily indexed with a primitive hexagonal unit cell [P$\overline 3 $ space group, Z = 6] similar to that already obtained for La0.33Zr2(PO4)3. Obtained unit cells parameters are [a = 8.3443(1) Å, c = 22.3629(1) Å], and [a = 8.3384(1), c = 22.3456(1) Å], respectively, for [Mg0.50] and [Ni0.50] phosphates. In both samples, the [Sb(Fe)(PO4)3]− NASICON framework is preserved and a partially-ordered distribution of Sb5+ and Fe3+ ions is observed. Raman spectroscopic study was used to obtain further structural information about the nature of bonding in [Mg0.50] and [Ni0.50] phases.

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