Pressure-induced transformations in crystalline and vitreous (original) (raw)
Related papers
Structural refinements of high-pressure phases in germanium dioxide
Acta Crystallographica Section B Structural Science, 2003
Recently, there has been substantial interest in the new high-pressure polymorphs of GeO2 synthesized in the laboratory. Previous investigators reported the synthesis of 'CaCl2-type', 'alpha-PbO2-type' and 'pyrite-type (modified-fluorite-type)' GeO2 at pressures of 30-130 GPa in laser-heated diamond anvil cells. In order to provide definitive information about the new high-pressure polymorphs, we performed Rietveld refinements of the structures. The structure refinements confirm that two of these high-pressure phases do have the alpha-PbO2-type and pyrite-type (modified-fluorite-type) structures.
Effect of uniaxial pressure on the ferroelectric phase transition in Pb 5 Ge 3 ) 11
Journal of Physics: Condensed Matter, 1999
The effect of uniaxial pressure up to 1 kbar applied perpendicular and parallel to c-axis, on the Curie temperature and electric permittivity εc of Ba-doped Pb 5 Ge 3 O 11 single crystals was investigated. The Curie temperature decreases with uniaxial pressure and the coefficient γi (γi ≡ δT c/δXi) is determined as -7 and -11 K kbar −1 for the b-and c-axes, respectively. It was found that uniaxial pressure increases the phase transition diffuseness and the tricritical point cannot be achieved for this pyroelectric and ferroelectric single crystal.
Isothermal and non-isothermal kinetic study of the PbGeO 3 solid–solid phase transition
Thermochimica Acta, 2005
A kinetics study on PbGeO 3 solid-solid phase transition was realised by means of differential scanning calorimetry and time-resolved X-ray powder diffraction. Isothermal and non-isothermal Johnson-Mehl-Avrami equations were applied to obtain both the activation energy E a and the Avrami coefficient n. The latter parameter has been related to morphological evidences collected by scanning electron microscopy. The limits of the applied theory, i.e., the Arrhenian behaviour of the growth rate and a steady-state nucleation rate, are finally discussed in terms of recent theoretical developments.
Pressure-induced amorphization of germanium diselenide
Journal of Non-Crystalline Solids, 1998
We have measured the Raman scattering spectra of b-GeSe single crystal high-temperature modification with layered 2 . crystal structure under hydrostatic pressures to 12.5 GPa at room temperature. According to the Raman spectra, the pressure Ž . increase produces transformation of the layered crystal structure into a fully disordered structure at 6.2 GPa . A further increase of the pressure to 7 GPa yields indications of a phase transition from the disordered phase to the a-GeSe 2 Ž . low-temperature modification of GeSe with three dimensional crystal structure . At 8 GPa, this modification transforms 2 back to the disordered phase. Reversibility of the phase changes, upon releasing the pressure, depends on the maximum pressure. q 1998 Elsevier Science B.V. All rights reserved.
Universal amorphous-amorphous transition in GexSe100−x glasses under pressure
Scientific Reports, 2016
Pressure induced structural modifications in vitreous GexSe100−x (where 10 ≤ x ≤ 25) are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15–20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distri...
High-pressure and high-temperature study of phase transitions in solid germanium
physica status solidi (b), 2003
A detailed investigation of the pressure and temperature dependence of the structure of stable and metastable solid Ge phases in the 0-15 GPa and 295-500 K ranges is presented. Structural results including the equation of state, characteristic of coexistence regions of diamond and b-tin structures, and appearance of metastable phases are discussed and compared with the results presently available in the literature. The isothermal bulk modulus and its derivative are evaluated using temperature-dependent equations of state for Ge I (cubic) and Ge II (b-Sn), and for the Ge III (ST12) metastable polymorph at 400 K.
THE STRUCTURE OF RAREFIED AND DENSIFIED PbGeO3 AND PbGeO2 GLASSES: A MOLECULAR DYNAMICS STUDY
Computational Methods in Science and Technology, 2001
The paper is dedicated to a molecular dynamics (MD) study of the structure of rarefied and densified lead-germanate glasses, of compositions PbGeO 3 and PbGeO 2. The simulations have been performed at constant volume for systems with densities of 3000, 4000, 5000, 6285 (normal density), 7000, and 8000 kg/m 3 , using a two-body potential (Born-Mayer repulsive forces, and Coulomb forces due to full ionic charges). All the systems were initially prepared as well equilibrated hot melts, and then slowly cooled down to 300 K. The information on short-range correlations was obtained in a conventional way (from radial and angular distribution functions), while the middle-range order was studied via cation-anion ring analysis. In the paper, the short-and medium-range order in the rarefied and densified glasses is discussed and compared with the structure of the PbGeO 3 and PbGeO 2 glasses at normal conditions.
Journal of Physics-condensed Matter, 2009
Structural transformations at high pressure in amorphous and quartz-like crystalline GeO 2 have been investigated by using a Paris-Edinburgh press coupled to EXAFS spectroscopy. From both the germanium absorption edge position and the Ge-O distance evolution, new detailed information has been obtained about the pressure behavior of the short range order. Crystalline GeO 2 undergoes a transformation from four-to six-fold coordination at about 8.5 GPa, but at least the whole 6-12 GPa pressure range should be considered as the transition region. On the other hand, amorphous GeO 2 is characterized by a much more gradual structural change and the full octahedral state is not reached at 13 GPa as commonly believed. Furthermore, no support to the recently claimed fully pentahedral intermediate state can be given. EXAFS signals of glassy GeO 2 beyond the first Ge-O shell qualitatively confirm the continuous breakdown of the intermediate range order up to 10 GPa.
Earth and Planetary Science Letters, 2010
a b s t r a c t Editor: L. Stixrude Keywords: high pressure generation sintered diamond Kawai-cell the postperovskite transformation MgGeO 3 the D″ layer High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes and the synchrotron radiation at SPring-8. The maximum attainable pressure reached 90.4 GPa at 300 K based on the Anderson et al. (1989) Au scale. Simultaneously, we investigated the perovskite (Pv)-postperovskite (PPv) transformation in MgGeO 3 up to ca. 74 GPa and 2200 K by means of in situ X-ray diffraction method.
Inorganic chemistry, 2017
We demonstrate that pressure-induced amorphization in Ge-Sb-Te alloys across the ferroelectric-paraelectric transition can be represented as a mixture of coherently distorted rhombohedral Ge8Sb2Te11 and randomly distorted cubic Ge4Sb2Te7 and high-temperature Ge8Sb2Te11 phases. While coherent distortion in Ge8Sb2Te11 does not prevent the crystalline state from collapsing into its amorphous counterpart in a similar manner to pure GeTe, the pressure-amorphized Ge8Sb2Te11 phase begins to revert to the crystalline cubic phase at ∼9 GPa in contrast to Ge4Sb2Te7, which remains amorphous under ambient conditions when gradually decompressed from 40 GPa. Moreover, experimentally, it was observed that pressure-induced amorphization in Ge8Sb2Te11 is a temperature-dependent process. Ge8Sb2Te11 transforms into the amorphous phase at ∼27.5 and 25.2 GPa at room temperature and 408 K, respectively, and completely amorphizes at 32 GPa at 408 K, while some crystalline texture could be seen until 38 GP...