Low-temperature specific heat of compacted vitreous silica

Liu, X.; Löhneysen, H. v.; Weiß, G.; Arndt, Jörg

doi:10.1007/s002570050009

Cited by 22 publications

(26 citation statements)

References 37 publications

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“…When plotted as C(T)/T 3 vs T (Figure 2), the specific heat for all the studied samples evidences the characteristic shape for a glass determined by an upturn below 2 K and a broad peak above 2 K. Growing densification depresses C(T) over the whole temperature interval explored giving rise to a significant decrease of the hump and to an increase of the peak temperature T peak , which shifts from about 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 that all the vibrational modes, extended and quasi-localized, contributing to the hump form a distribution which is independent of density. Both the observations discussed above are in agreement with the results of studies concerning the low temperature specific heat in compacted SiO 2 [11] and in situ high pressure inelastic neutron scattering measurements on poly-isobutylene (PIB) [21,22]. Even if, as pointed out in SiO 2 [23], measurements with in situ applied pressure cannot be simply compared to the observations in permanently densified samples retrieved from the same interval of pressure, these results concerning the low energy vibrational dynamics appear to be quite general and independent of the specific experimental conditions.…”

Section: Resultssupporting

confidence: 81%

“…, in densified glasses shows that growing densification appears to be more efficient in depressing the LEE contributing to the hump than TLS responsible for nearly linear specific heat below 1 K. In fact, [11], where C is reduced by about the same factor over the whole temperature range explored (0.1 K<T<35 K), and suggests a possible different microscopic origin for the low energy excitations giving rise to TLS and to the hump (or the BP) in GeO 2 glass. Previous neutron and x-ray diffraction studies [18,28] of densified GeO 2 glasses gave strong evidence for a reduction in the length scale of the intermediate-range order induced by cold densification up to 10 GPa, excluding a transition from a GeO 4 tetrahedral to a GeO 6 octahedral structure.…”

Section: Resultsmentioning

confidence: 99%

“…With the aim of investigating the relation between quantum tunnelling and additional vibrations governing the THz region, we present here a study concerning the low temperature specific heat in GeO 2 glasses, permanently densified by increasing pressures. Differently from the observations in compacted v-SiO 2 where coherent changes of the specific heat were revealed over the whole temperature interval explored [11], the present results show that, above 1 K, the specific heat C is significantly reduced with increasing density exhibiting variations stronger than those observed below 1 K. As explained in the following, these differences are believed to be a consequence of a wider range of investigated densifications (more than 20 %) which cause more substantial modifications of the intermediate range order.…”

Section: Introductionmentioning

confidence: 93%

“…Permanent densification makes it possible to study indirectly the effects of pressure on physical properties, such as the thermodynamic measurements, for which it is usually difficult to carry out in situ high pressure experiments. Remarkable changes are in fact observed in the linear specific heat [11], the hump in C/T 3 and the frequency of the Boson Peak [12][13][14][15], and also in the internal friction [16] and the sound velocity [17]. Measurements on permanently densified samples can provide information on the microscopic mechanisms governing the LEE, mainly when the observations are compared with the microscopic structural changes.…”

Section: Introductionmentioning

confidence: 99%

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Low temperature specific heats of permanently densified glassy GeO₂

Carini¹,

Carini²,

D’Angelo³

et al. 2011

Philosophical Magazine

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Section: Resultssupporting

confidence: 81%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Low temperature specific heats of permanently densified glassy GeO₂

Carini¹,

Carini²,

D’Angelo³

et al. 2011

Philosophical Magazine

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“…The observed strong dependence of the density of states on the inter-tetrahedral structure [30] fits in this picture, since the relevant Si-O-Si angle is the most important parameter for the inter-tetrahedral structure.…”

mentioning

confidence: 53%

What Is Moving in Silica at 1 K? A Computer Study of the Low-Temperature Anomalies

Reinisch

Heuer

2005

Phys. Rev. Lett.

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Though the existence of two-level systems (TLS) is widely accepted to explain low temperature anomalies in many physical observables, knowledge about their properties is very rare. For silica which is one of the prototype glass-forming systems we elucidate the properties of the TLS via computer simulations by applying a systematic search algorithm. We get specific information in the configuration space, i.e. about relevant energy scales, the absolute number of TLS and electric dipole moments. Furthermore important insight about the real-space realization of the TLS can be obtained. Comparison with experimental observations is included.PACS numbers: 61.43.Fs, 63.50.+x, Most kinds of disordered solids show anomalous behavior at very low temperatures (Kelvin regime and below) as compared to their crystalline counterparts. Many of the observed features can be explained by the Standard Tunneling Model (STM) [1,2] and its generalization, which is the Soft-Potential Model [3,4]. The basic idea of the STM is to postulate the possibility of localized transitions between different configurations, i.e. adjacent minima of the potential energy landscape. Such a transition can be described by a double-well potential (DWP), characterized by an asymmetry ∆, potential height V and distance d between both configurations. From a quantum-mechanically perspective at low temperatures the system is tunneling between both configurations and the DWP is characterized by the lowest two eigenstates. If their energy difference E is in the Kelvin regime, these DWP may contribute to the low-temperature anomalies. Then one may speak of Two Level Systems (TLS). The TLS can couple to strain and electric fields and therefore show up in observables like thermal conductivity, sound absorption and dielectric response [5]. Recently, even observations about the interaction of different TLS have been reported [6,7,8].So far it has not been possible to derive a theory of the low-temperature anomalies of real glass-forming systems from first principles, except for mean-field models [9] and random first order transition theory [10]. Thus for a prototype system like SiO 2 the STM has to be basically considered as phenomenological. Important questions emerge. Computer simulations may help to shed some light on the nature of the low-temperature anomalies. In previous work on SiO 2 the trajectories, generated either by molecular dynamics [11,12] or by the activationrelaxation technique [13], have been analyzed with respect to transition events between different structures. Both approaches yield some interesting insight into the nature of relaxation processes in SiO 2 . (Q1), however, requires a systematic search procedure, and (Q2) and (Q3) a sufficiently large number of characteristic DWP and thus an efficient search method. This has not been the scope of previous simulations on SiO 2 .In recent years we have developed a set of simulation techniques which allow us to approach these questions [14,15]. (Q1) Starting from representative low-energy structures we...

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