Vibrational properties of amorphous germanium under pressure and its thermal expansion and Grüneisen parameters

Durandurdu, Murat

doi:10.1016/j.jnoncrysol.2010.01.028

Cited by 5 publications

(7 citation statements)

References 51 publications

(63 reference statements)

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“…This HDA–LDA transformation is fully characterized for the first time using Raman spectroscopy, thanks to the low-frequency access allowed by our Raman spectrometer. The Raman signal is in agreement with the numerical simulations available in the literature. , The PIA followed by a polymorphic transformation upon decompression is similar to the observations in Ge nanoparticles. In the following, we discuss first the pressure-induced phase transformations using a classical thermodynamics approach.…”

Section: Resultssupporting

confidence: 89%

“…This value is in very good agreement with the experimental data that gives γ ≈ −0.8. This measurement fills an experimental deficiency noted by theoreticians as “no information reported in the literature about the response of the low-frequency modes of a-Ge to pressure and Grüneisen parameters of a-Ge” …”

Section: Resultssupporting

confidence: 52%

“…On the other hand, in amorphous Ge, a general property of this low-frequency peak is an increase in its amplitude as the structural order of the samples decreases . In addition, standard and ab initio molecular dynamics simulations show that in the LDA state of Ge, the low-frequency band is as intense as the high-frequency one. , This indicates that the nanostructure is getting more and more disordered with increasing pressure. This effect starts right from the first pressure steps, as a mesoporous structure is very sensitive to stress application.…”

Section: Resultsmentioning

confidence: 98%

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Metastable States in Pressurized Bulk and Mesoporous Germanium

et al. 2018

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Combination of porosity and hydrostaticity during compression is used with a view to explore the energy landscape of germanium. In this work, pressure-induced phase transformations in mesoporous crystalline Ge has been investigated by in situ Raman spectroscopy. A pressure-induced amorphization to a low-density amorphous (LDA) state was observed prior to a reversible polyamorphic transformation between LDA and high-density amorphous states. These pressure-induced transformations show some similarities with the behavior previously reported in nanoparticles. Thermodynamics models developed in the case of nanoparticles are successfully used indicating that, in both cases, the large surface-to-volume ratio leads to an increase of the system energy and that mesoporous materials may be considered as the negative image of a collection of nanoparticles. However, an inhomogeneous stress distribution is expected in porous materials because of it being a network with hyperbolic geometry. A control experiment is presented using a reference bulk germanium sample. The diamond-to-β-tin transformation is observed starting at around 8.0 GPa. On decompression, the metastable ST12 (Ge-III) phase is observed. Ab initio simulations are used to assign and interpret Raman spectra of this phase.

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Section: Resultssupporting

confidence: 89%

Section: Resultssupporting

confidence: 52%

Section: Resultsmentioning

confidence: 98%

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Metastable States in Pressurized Bulk and Mesoporous Germanium

et al. 2018

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“…The average CTE of Cs (1− x ) Na x GP ceramics continued to rise as the sodium content increases. Compared with pollucite (~4.80×10 −6 K −1 ), amorphous glass‐phase‐contained sodium always had a higher CTE than that of pollucite (9~10×10 −6 K −1 ) . In contrast, the effect on CTE caused by the presence of the amorphous glass phase was much stronger than the impact caused by the substitution of Na + for Cs + in lattice level.…”

Section: Resultsmentioning

confidence: 91%

Effects of Na⁺ substitution Cs⁺ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer

Yuan

Jia

et al. 2017

J Am Ceram Soc

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As part of a series of studies, effects of Na + substitution on the thermal evolution of cesium-based geopolymers on heating were studied. A series of sodiumsubstituted cesium-based geopolymers, Cs (1Àx) Na x GPs (where x=0, 0.1, 0.2, 0.3, and 0.4), were prepared and treated at 1300°C for 2 hours to obtain the corresponding ceramic products. The thermal evolution process was disclosed by virtue of a variety of technical, including TG-DTA, thermal shrinkage, XRD analysis, SEM, and TEM investigation. The results indicated that unheated Cs (1Àx) Na x GPs was not completely amorphous after the substitution of Na + and the crystallinity of Cs (1Àx) Na x GPs gradually increased with the rise of sodium content. Meanwhile, the average particle sizes of Cs (1Àx) Na x GPs also increased evidently with increases in sodium substitution. The final product after heat treatment mainly consisted of pollucite (CsAlSi 2 O 6 ) and amorphous glass phase. The particle size of pollucite grain gradually decreased as more Cs + were replaced maybe owing to the role of Na + in the nucleation process of pollucite. Two forms of Na + present in the final products: A small portion was present in the pollucite grains due to Na + partial occupied the crystallographic sites of Cs + ; and the rest were present in the amorphous glass phase among the pollucite grains. The average coefficient of thermal expansion (CTE) of resulting Cs (1Àx) Na x GPs ceramics increased from 4.80910 -6 K À1 (x=0) to 7.26910 À6 K À1 (x=0.4) with increases in sodium substitution, which could be due to the amorphous glass phase had a relatively higher CTE than that of pollucite. K E Y W O R D Sgeopolymer, high-temperature treatment, microstructure, pollucite, thermal expansion 1 | INTRODUCTION Radioisotopes of cesium ( 137 Cs and 134 Cs) were very soluble in water and the resulting radiation would spread to a wide area and continue to radiate to the surrounding for a long time, even for centuries, which had become the largest problems after nuclear accidents in Chernobyl and Fukushima. 1-3 Pollucite, with stoichiometric formula of CsAlSi 2 O 6 , had a cubic Ia-3d symmetry with a zeolite-like structure. The structural channels in pollucite were constructed by six-oxygen rings and had a diameter of only 2.8 A, which was smaller than the diameter of the Cs + of 3.34 A. 4-7 Radioactive Cs + will be encapsulated after the formation of pollucite and the trapped Cs + would not be

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“…The average CTE of Cs (1-x) Na x GP ceramics continued to rise with the increase in content of Na + ion introduction. It is well known that amorphous glass phase containing Na + ion always had a higher CTE (9~10 × 10 −6 K −1 ) than that of pollucite (~4.80 × 10 −6 K −1 ) [53][54][55][56]. By contrast, the effect on CTE caused by the presence of the amorphous glass phase was much stronger than the impact caused by the substitution of Na + for Cs + in lattice level.…”

Section: Thermal Expansion Behaviormentioning

confidence: 99%

Thermal Evolution of Geopolymer in the Process of High-Temperature Treatment

Yuan¹,

He²,

Jia³

2020

Geopolymers and Other Geosynthetics

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More and more attention had been given to geopolymers (GPs) over the last decades because of an increasing urgency to search for high-performance and/or environment-friendly alternatives to traditional Portland cement. In addition, geopolymer technology could also provide an innovative approach to prepare advanced ceramic products by overcoming problems faced in the conventional preparation technology. With only the need to go through appropriate thermal treatment procedure, geopolymers could be directly in situ transformed into advanced ceramics such as leucite or pollucite with adjustable microstructures, mechanical properties, coefficient of thermal expansion, and melting points. In the process of high-temperature treatment, multiple parameters, such as the composition of geopolymer, treatment temperature, thermal insulation, etc., would affect the phase composition and microstructure of the resulting products. In the present chapter, two kinds of mixed-alkali metal ion-activated geopolymer systems, Cs (1-x) Li x GP (where x = 0, 0.1, 0.2, and 0.3) and Cs (1-x) Na x GP (where x = 0, 0.1, 0.2, 0.3, and 0.4), respectively, were designed and prepared. Phase composition, microstructure evolution, and thermal expansion behaviors of the ceramics derived from the geopolymers were characterized and the effects of ion substitution on the thermal evolution of geopolymer were evaluated.

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Vibrational properties of amorphous germanium under pressure and its thermal expansion and Grüneisen parameters

Cited by 5 publications

References 51 publications

Metastable States in Pressurized Bulk and Mesoporous Germanium

Metastable States in Pressurized Bulk and Mesoporous Germanium

Effects of Na⁺ substitution Cs⁺ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer

Thermal Evolution of Geopolymer in the Process of High-Temperature Treatment

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Vibrational properties of amorphous germanium under pressure and its thermal expansion and Grüneisen parameters

Cited by 5 publications

References 51 publications

Metastable States in Pressurized Bulk and Mesoporous Germanium

Metastable States in Pressurized Bulk and Mesoporous Germanium

Effects of Na+ substitution Cs+ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer

Thermal Evolution of Geopolymer in the Process of High-Temperature Treatment

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Effects of Na⁺ substitution Cs⁺ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer