Logarithmic Kinetics of the Amorphous-Amorphous Transformations in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>SiO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>GeO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>Glasses under High Pressure

Tsiok, O. B.; Бражкин, В. В.; Lyapin, A. G.; Khvostantsev, L. G.

doi:10.1103/physrevlett.80.999

Cited by 235 publications

(143 citation statements)

References 35 publications

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“…These sample volume measurement results indicate its average values, which are contributed from the time-dependent volume fraction of a-Se, m-Se, and t-Se in sample. At fixed high-pressure conditions, the compaction (densification) over time has been reported in the disordered systems due to relaxation; for example, the molar volume of GeO 2 glass at 7 GPa continually decreases about 1.2% over Ϸ100 min (37). The direct measurement of the pressure-induced volume expansion phenomenon documented here appears not to have been previously reported.…”

Section: Resultsmentioning

confidence: 43%

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Liu

Wang

Xiao

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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The high-pressure behavior of amorphous selenium has been investigated with time-resolved diamond anvil cell synchrotron x-ray diffraction and computed microtomography techniques. A two-step dynamic crystallization process is observed in which the monoclinic phase crystallized from the amorphous selenium and gradually converted to the trigonal phase, thereby explaining previously observed anomalous changes in electrical conductivity of the material under pressure. The crystallization of this elemental system involves local topological fluctuations and results in an unusual pressure-induced volume expansion. The metastability of the phases involved in the transition accounts for this phenomenon. The results demonstrate the use of pressure to control and directly monitor the relative densities and energetics of phases to create new phases from highly metastable states. The microtomographic technique developed here represents a method for determination of the equations of state of amorphous materials at extreme pressures and temperatures.crystallization ͉ volume expansion ͉ equation of state ͉ phase transition ͉ metastability T he behavior of amorphous materials under pressure is a problem of great current interest. Unusual behavior, such as pressure-induced amorphization of crystalline forms, pressureinduced polyamorphism low-to high-density forms of insulating and metallic glasses, and the dynamics of pressure-induced crystallization are reported but not fully understood (1-10). The nature of the behavior of amorphous solids under pressure is complicated by their metastability and the possibility of irreversible relaxation of their properties and structure (11). Amorphous selenium (a-Se) is a model system for examining pressure effects in amorphous materials because of the wide range of structure and bonding properties expected based on the behavior of the crystalline polymorphs of the element. In experiments designed to understand the high-pressure behavior of a-Se, we have discovered an unexpected pressure-induced dynamic crystallization process associated with a volume expansion in the material. The origin of this unusual phenomenon is examined by using a microtomography technique that allows direct measurement of the equation of state (EOS) of the amorphous phase.Recent efforts to characterize the structural evolution of group VI elements under pressure, such as novel dense chain structures in sulfur and selenium (12), and the alternating phase transition sequence in sulfur at high pressure and temperature (13), have led to a new level of understanding of the phase diagrams and structures of these materials. Under pressure, selenium exhibits a complex polymorphism, and the diversity of phases and transition sequences observed depend strongly on the starting material (12,(14)(15)(16)(17)(18)(19)(20)(21). First studied by x-ray diffraction (XRD) in 1972 (22), a-Se was found to crystallize in a trigonal structure (t-Se) at Ϸ10 GPa (23-27). However, its electrical resistance was clearly different from pure t-Se i...

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Section: Resultsmentioning

confidence: 43%

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Liu

Wang

Xiao

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…Although the samples are almost the same size at 0 GPa, the sample in methanol-ethanol is obviously smaller than that in helium at 9 GPa. 6 , respectively. The volume change in methanol-ethanol measured in this study is consistent with those in previous studies, indicating that the low compressibility in helium cannot be attributed to problems in the sample and/or method of measurements.…”

Section: Resultsmentioning

confidence: 97%

“…SiO 2 glass is compressible among silicates (or oxides) [4][5][6][7] because it has a structure with a significant amount of interstitial voids 8 . Elastic softening and permanent densification of SiO 2 glass under high pressure are interesting issues in physics and materials science [4][5][6][9][10][11][12] and closely related to deformation and compaction of these voids. Information on the pressure dependence of its structure and density is also important in geophysics, because glasses can be considered as the analogue material of melts 11,13 .…”

mentioning

confidence: 99%

Helium penetrates into silica glass and reduces its compressibility

2011

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SiO 2 glass has a network structure with a significant amount of interstitial voids. Gas solubilities in silicates are expected to become small under high pressure due to compaction of voids. Here we show anomalous behaviour of SiO 2 glass in helium. Volume measurements clarify that SiO 2 glass is much less compressible than normal when compressed in helium, and the volume in helium at 10 GPa is close to the normal volume at 2 GPa. X-ray diffraction and Raman scattering measurements suggest that voids are prevented from contracting when compressed in helium because helium penetrates into them. The estimated helium solubility is very high and is between 1.0 and 2.3 mol per mole of SiO 2 glass at 10 GPa, which shows marked contrast with previous models. These results may have implications for discussions of the Earth's evolution as well as interpretations of various high-pressure experiments, and also lead to the creation of new materials.

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“…Owing to the larger compressibility of the SiO 2 matrix (∼0.027 GPa −1 ) [30] relative to Si (∼0.01 GPa −1 in bulk samples) [24], the NCs may be subject to an effective pressure which is enhanced in relation to the applied (hydrostatic) pressure. Similar observations have been reported in Ge NCs embedded into SiO 2 [31] and also in thin layers grown on more compressible substrates (see for instance the recent high-pressure Raman scattering study on InGaN/Si(111) epilayers) [32].…”

Section: Resultsmentioning

confidence: 99%

Optical emission fromSiO2-embedded silicon nanocrystals: A high-pressure Raman and photoluminescence study

et al. 2015

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We investigate the optical properties of high-quality Si nanocrystals (NCs)/SiO 2 multilayers under high hydrostatic pressure with Raman scattering and photoluminescence (PL) measurements. The aim of our study is to shed light on the origin of the optical emission of the Si NCs/SiO 2 . The Si NCs were produced by chemical-vapor deposition of Si-rich oxynitride (SRON)/SiO 2 multilayers with 5-and 4-nm SRON layer thicknesses on fused silica substrates and subsequent annealing at 1150°C, which resulted in the precipitation of Si NCs with an average size of 4.1 and 3.3 nm, respectively. From the pressure dependence of the Raman spectra we extract a phonon pressure coefficient of 8.5 ± 0.3 cm −1 /GPa in both samples, notably higher than that of bulk Si (5.1 cm −1 /GPa). This result is ascribed to a strong pressure amplification effect due to the larger compressibility of the SiO 2 matrix. In turn, the PL spectra exhibit two markedly different contributions: a higher-energy band that redshifts with pressure, and a lower-energy band which barely depends on pressure and which can be attributed to defect-related emission. The pressure coefficients of the higher-energy contribution are (−27 ± 6) and (−35 ± 8) meV/GPa for the Si NCs with a size of 4.1 and 3.3 nm, respectively. These values are sizably higher than those of bulk Si (−14 meV/GPa). When the pressure amplification effect observed by Raman scattering is incorporated into the analysis of the PL spectra, it can be concluded that the pressure behavior of the high-energy PL band is consistent with that of the indirect transition of Si and, therefore, with the quantum-confined model for the emission of the Si NCs.

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Logarithmic Kinetics of the Amorphous-Amorphous Transformations inSiO2andGeO2Glasses under High Pressure

Cited by 235 publications

References 35 publications

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Helium penetrates into silica glass and reduces its compressibility

Optical emission fromSiO2-embedded silicon nanocrystals: A high-pressure Raman and photoluminescence study

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