Search results for "FFR"
showing 10 items of 1798 documents
First-Order Isostructural Phase Transition Induced by High Pressure in Fe(IO3)3
2020
The high-pressure (HP) behavior of Fe(IO3)3 was studied up to 35 GPa using powder X-ray diffraction, infrared micro-spectroscopy, and ab initio density-functional theory calculations. Fe(IO3)3 show...
High-pressure structural transformations of PbCrO4 up to 51.2 GPa: An angle-dispersive synchrotron X-ray diffraction study
2014
Abstract We report on high-pressure X-ray diffraction measurements up to 51.2 GPa in PbCrO 4 at room temperature. Three high-pressure phases with structures different than the ambient-pressure monazite-type ( P 2 1 / n ) are reported. One phase transition was found at 3.8 GPa to an isomorphic structure to monazite. A second transition occurs at 11.1 GPa. After this transition, the coexistence of tetragonal ( I 4 1 / a ) and monoclinic ( P 2 1 ) structures is detected up to 21.1 GPa. Beyond this pressure and up to 51.2 GPa, only the high-pressure monoclinic phase is observed. Upon decompression all structural changes are reversible. Finally, the axial compressibilities for the different phas…
Heterovalent ion replacement in bi7Ti4NbO21: Some new compounds and phase transitions
1996
Abstract Simultaneous heterovalent substitutions at two cationic sites of the bismuth mixed-layered compound Bi7Ti4NbO21 have been made. Two new compounds: Bi2Pb⅓Ti(4/3)Mo⅓O7 and Bi(4/3)PbTiMo⅔O7, were obtained and identified by X-ray diffraction analysis. A model of possible mixed layer structure is discussed. Ferroelectric phase transitions at 510°C and 550°C have been studied by dielectric measurements.
Pressure-induced amorphization of YVO4:Eu3+ nanoboxes
2016
A structural transformation from the zircon-type structure to an amorphous phase has been found in YVO4:Eu3+ nanoboxes at high pressures above 12.7 GPa by means of x-ray diffraction measurements. However, the pair distribution function of the high-pressure phase shows that the local structure of the amorphous phase is similar to the scheelite-type YVO4. These results are confirmed both by Raman spectroscopy and Eu3+ photoluminescence which detect the phase transition to a scheelite-type structure at 10.1 and 9.1 GPa, respectively. The irreversibility of the phase transition is observed with the three techniques after a maximum pressure in the upstroke of around 20 GPa. The existence of two …
An electron diffraction study of deposited docosanoic acid monolayers
1991
Docosanoic acid monolayers deposited on thin polymer films under different water surface conditions have been investigated using transmission electron diffraction at normal and tilted incidence. Diffraction patterns obtained from the L2 and L2' phase are quite similar, but distinctly different to samples coated from the CS phase. The former were consistent with molecules perpendicular to the substrate, arranged in a texture of grains with unusual orthorhombic packing. There is evidence for a phase transition from a liquid crystalline phase on the water surface.
AB$$_{2}$$O$$_{4}$$ Compounds at High Pressures
2014
In this chapter, we present an overview of the effects of pressure on the crystalline structure and physical properties of oxygen-based spinels and other related oxides. Recent X-ray diffraction and Raman spectroscopy studies are summarized. A brief description of pressure-driven transitions and post-spinel structures is also provided. We also compare the response to high-pressure of several spinel oxides. We conclude with an examination of elastic and magnetic properties.
High-pressure transition to the post-barite phase in BaCrO4hashemite
2012
A recent high-pressure study on barium chromate BaCrO${}_{4}$ reported a phase transition but the structure of the high-pressure phase structure could not be identified. This high-pressure phase was suggested to have a monoclinic structure different from other high-pressure forms of $AB$O${}_{4}$-type compounds. In this work, we have carried out x-ray diffraction measurements up to 46 GPa using He as the quasihydrostatic pressure medium and density-functional theory calculations. Our studies allow us to identify the high-pressure phase as the $P$2${}_{1}$2${}_{1}$2${}_{1}$ post-barite-type phase, recently reported for BaSO${}_{4}$. The equations of state of both, the low- and the high-press…
Mechanisms at structural phase transitions
2007
Abstract Structural phase transitions in crystalline solids are accompanied with the change of symmetry. After EHRENFEST [Ehrenfest, P., Phasenumwandlungen im ublichen und erweiterten Sinn, klassifiziert nach den entsprechenden Singularitaten des thermodynamischen Potentials. Proc. Kon., Amsterdam Acad., 1933, 36(Suppl 75b), 153–157] they can be distinguished between first and second order transitions. Two examples for first and second order transitions will be discussed in order two elaborate the characteristic features. The statements are verified by diffraction experiments; the second order transitions will be discussed on the basis of the LANDAU [Landau, L. and Lifshitz, E.M., Lehrbuch …
High-pressure structural phase transition inMnWO4
2015
The pressure-induced phase transition of the multiferroic manganese tungstate MnWO4 is studied on single crystals using synchrotron x-ray diffraction and Raman spectroscopy. We observe the monoclinic P2/c to triclinic P (1) over bar phase transition at 20.1 GPa and get insight on the phase transition mechanism from the appearance of tilted triclinic domains. Selective Raman spectroscopy experiments with single crystals have shown that the onset of the phase transition occurs 5 GPa below the previously reported pressure obtained from experiments performed with powder samples.
X-ray Studies of Debye Temperature of Some ABO 3 Perovskites
2002
Debye temperatures T D of some perovskite compounds are determined by X-ray diffraction. Correlation between T D determined at T=180 °C, mean square displacements of atoms, quasi-elastic coupling, and melting temperature of the perovskite compounds is analysed.