Low-temperature anomalies

At temperatures say, below 70 K further relaxation processes occur. There, the frequency dependence of "(v) changes from a negative slope to a positive one. In this temperature range, thermally activated dynamics in asymmetric double-well potentials (ADWP) and, below 10 K, tunneling phenomena were discussed relating to the so-called low-temperature anomalies of glasses.27,30,31... 

Although the origin of low temperature anomaly is unclear, the low pressure anomaly has been attributed to the presence of two different populations of Si-O-Si bond angles. The Si-O-Si bond angle distribution is... 

Although Si02 is a typical inorganic glass, it is also atypical in many ways. Several properties of vitreous silica are known to vary anomalously at low temperatures. Anomaly in the low temperature specific heat is the most notable and well investigated. This is reflected in serious disagreement between Debye temperatures calculated from thermal and acoustic measurements. (thermal) and(elastic) are respectively given by (Anderson and Dienes, 1960),... 

The known low-temperature anomaly of water is interesting by itself and is connected with the, so-called, reentrant spinodal form of liquid branch P p(T) in the range [T, Tt. This behavior has been investigated by Speedy in... 

The peculiarity of glasses (not only metallic ones), is the presence of a wide spectrum of low-energy excitations (with energies from 10 5 to 1 eV) exhibiting themselves in low-temperature anomalies of specific heat and thermoconductance, in the temperature dependence of the velocity and absorption coefficient of sound, in internal friction, and in a number of other relaxation phenomena. In describing the phenomena listed, various phenomenological models are in-... 

Early investigations of the effect of water on the low-temperature relaxations of several aromatic polymers including polycarbonate, polyamides, and a polyurethane have shown several low-temperature anomalies (A .5). the case of a water-saturated... 

A transition near 28 K at submonolayer coverages was discovered in a heat capacity study [73] (see the small low-temperature anomaly in Fig. 10) and interpreted in terms of a libration-hindered orientational transition of the molecular axes which occurs in bulk N2 around 36 K between the fee a solid and the hep 13 phase (see Table I). It was speculated that the monolayer... 

As clear from discussions given above and also in early chapters of the book, the area of low-temperature anomalies of water has drawn tremendous attention fijom scientists of all spheres, particularly fijom theoreticians and simulation experts. Despite all these efforts, this is one area which has remained controversial and a consensus about the origin of the anomalies remains elusive. One of the reasons perhaps is the presence of a no-man s-land , which is meant to mean the temperature zone between 155 K and 232 K. When cooled below 232 K, water always... 

We have also described several advanced topics devoted to neat bulk water, such as the freezing of water and also supercritical water. Both have attracted considerable attention in recent times. The low-temperature anomalies of water are slowly being understood, although the field remains the subject of lively debate. 

Fig. 35. Elastic constants of (a) CcAl, (Luthi and Yoshizawa 1987) and (b) CeB (Niksdi et al. 1980) showing pronounced low-temperature anomalies. The softening observed is explained via the action of the Kondo effect on the lattice.

Fig. 36. Elastic constants of UPtj show similar low-temperature anomalies to those of Ce compounds, cf. fig. 35 (Yoshizawa et al. 1985).

Mier-y-Teran, L., D. Boda, D. Henderson, and S. E. Quinones-Cisneros. 2001. On the low temperature anomalies in the properties of the electrochemical interface. A nonlocal free-energy density functional approach. Molecular Physics An International Journal at the Interface between Chemistry and Physics 99, no. 15 1323. doi 10.1080/00268970110048383. 

In the region where magnetic effects must be considered, a resistivity study on CeHj+ c (0 < X < 0.01) by Vajda et al. (1990) shows that the appearance of low-temperature anomalies related to magnetic transitions depends on whether the system is cooled slowly enough for ordering to occur. Both heavy-fermion and Kondo-lattice behaviors are inferred from the low-temperature results (T<20K) and a close competition between magnetic order and the Kondo effect is revealed by data from quenched versus slow-cooled samples. 

Thus one expects a low temperature anomaly in the thermopower due to the crystal-field splitting. Such an anomaly has indeed been observed by Umlauf et al. (1973) on Lai-xTb Al2. Their experimental findings are shown in fig. 17.11. The ground state of Tb is a nonmagnetic doublet Fi with a first excited state (F4) at 5 K. This requires a generalization of eq. (17.60). Under the assumption that the elastic Coulomb scattering is the same for each level one finds for a multi-level system... 

To get an idea about the scale of similar low-temperature anomalies in more realistic systems in which the not-nearest-neighbor-interactions n >i are also present, we used COE to calculate the concentration and temperature dependences [Pg.414]

All the TLS existing in a polymer with impurity centres can be divided into two groups extrinsic TLS and intrinsic TLS. The intrinsic TLS are spread throughout the whole bulk of a solvent. The distance between intrinsic TLS and an impurity chromophore, a rule, is large. Chromophores do not affect these TLS and they determine bulk properties of a polymer at low temperature. These very TLS are responsible for the low temperature anomalies in heat capacity. 

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