Heat capacity, Raman, and Brillouin scattering studies of M2O–MgO–WO3–P2O5 glasses (M=K,Rb)

Abstract

The authors report the results of temperature-dependent Brillouin scattering from both transverse and longitudinal acoustic waves, heat capacity studies as well as room temperature Raman scattering studies on M 2 O-MgO-WO 3 -P 2 O 5 glasses ͑M=K,Rb͒. These results were used to obtain information about structure and various properties of the studied glasses such as fragility, elastic moduli, ratio of photoelastic constants, and elastic anharmonicity. They have found that both glasses have similar properties but replacement of K + ions by Rb + ions in the glass network leads to decrease of elastic parameters and P 44 photoelastic constant due to increase of fragility. Based on Brillouin spectroscopy they show that a linear correlation between longitudinal and shear elastic moduli holds over a large temperature range. This result supports the literature data that the Cauchy-type relation represents a general rule for amorphous solids. An analysis of the Boson peak revealed that the form of the frequency distribution of the excess density of states is in agreement with the Euclidean random matrix theory. The reason of the observed shift of the maximum frequency of the Boson peak when K + ions are substituted for Rb + ions is also briefly discussed.

Ultraviolet and visible Brillouin scattering study of viscous relaxation in 3-methylpentane down to the glass transition

“…30,31 In Figure 10 we show that a 5/3 slope describes adequately the data below 140 K yielding A 2.4 GPa or A/ρ 3 × 10 6 m 2 /s 2 similar to what found in glycerol 32 and in a variety of glass formers 30 but definitely larger than the value found in some phosphate glasses. 31 Finally, as far as the zero frequency bulk modulus is concerned, we wish to point out that although we have assumed K ∞ − K 0 to be constant and equal to its low temperature limit of ∼0.55 GPa, we can reasonably assume this quantity de-creases smoothly with increasing temperature so that K ∞ (T ) K 0 (T ) + 0.55 GPa (19) and consequently M ∞ (T ) K 0 (T ) + 4 3 G ∞ (T ) + 0.55 GPa. (20) The validity of this upper limit can in principle be checked performing higher frequency scattering experiments such as inelastic x-ray or neutron scattering from which M ∞ (T) is directly measured.…”

Mixed-Alkali Effect in Borate Glasses: Thermal, Elastic, and Vibrational Properties

“…Poisson's ratio, σ, is defined as the ratio between the transverse contraction strain and longitudinal extension strain in a stretched bar. Previous studies of the relation of the Poisson's ratio with the glass structure showed that it was greater than 0.25 when the ions themselves are deformed under stress in addition to the network distortion [28,29]. The alkali content dependences of Poisson's ratio, σ, of the single-alkali borate glasses are shown in Figure 6b.…”

“…However, most glasses are far from the central potential and the Cauchy relation, L = 3µ. The Cauchy-type relation, L = A + Bµ with B~3, was reported to hold for the high frequency limit values of the L and the µ for some types of glasses, where A is the material dependent constant [29,33].…”

Pressure dependence of Poisson’s ratio of glassy Baltic amber studied by Brillouin scattering spectroscopy

“…The number of independent elastic constants is only two, namely, the longitudinal (L or c 11 ) and the shear (G or c 44 ) modulus, where c 11 and c 44 are the elastic stiffness constants in isotropic systems. Additional local symmetry conditions 32) The studied oxide glasses were characterized by relatively weak elastic anharmonicity in comparison with polymer glasse, that have higher fragility. Such difference obeys the correlation between the fragility and the Grüneisen parameters, since the anharmonisity increases as the fragility increases.…”