Influence of cation size on the low-temperature heat capacity of alkaline earth metasilicate glasses

Boson Peak, Elastic Properties, and Rigidification Induced by the Substitution of Nitrogen for Oxygen in Oxynitride Glasses

“…In binary alkali silicates, low‐frequency localized modes involving network‐modifying cations also contribute to the boson peak, the importance of this contribution increasing with the ionic radius and mass of the cation 13 . A similar trend is observed in C p measurements for alkaline‐earth silicate glasses where Mg 2+ and Ca 2+ depress the boson peak, whereas Ba 2+ and Sr 2+ enhance it 31 . Although calorimetric data are lacking for Y 2 O 3 –SiO 2 glasses, the somewhat smaller size (0.98 vs 1.08 Å) 32 but much higher mass (88.9 vs 40.0 g/mol) of Y 3+ compared with those of Ca 2+ suggests that the former network‐modifying cation should not have stronger depressing effects on the boson peak than the latter.…”

“…24 Nitrogen does not bond to Al in oxynitride glasses. 27,28 In both Y and Ca28 series, the Al content is low enough for Al 31 to be a network former charge compensated by either Y 31 or Ca 21 . In the Y series, De´riano 18 found that about 20% and 6% of Al are in five-and sixfold coordination, respectively.…”

“…13 A similar trend is observed in C p measurements for alkaline-earth silicate glasses where Mg 21 and Ca 21 depress the boson peak, whereas Ba 21 and Sr 21 enhance it. 31 Although calorimetric data are lacking for Y 2 O 3 -SiO 2 glasses, the somewhat smaller size (0.98 vs 1.08 Å ) 32 but much higher mass (88.9 vs 40.0 g/mol) of Y 31 compared with those of Ca 21 suggests that the former network-modifying cation should not have stronger depressing effects on the boson peak than the latter. A second cause explaining the 50% smaller boson peak of the N-free Ca28-O and Y1 in comparison with a-SiO 2 could also be their much larger atomic packing density due to the presence of modifying and compensating cations, which should restrict librational motion.…”

Boson peak of alkali and alkaline earth silicate glasses: Influence of the nature and size of the network-modifying cation

“…19,20 The other glasses, namely, Sr and Ba whose preparation is made difficult either by high liquidus temperature or by poor glass forming ability, were prepared as 30-mg levitating, laserheated droplets that vitrified upon laser power cut-off. 21 In these cases, the calorimetric measurements were made by heat-pulse relaxation calorimetry 25 on a single glass droplet. In spite of such experimental differences, the coherence of the results obtained with both kinds of procedures has been noted in a comprehensive study of calcium aluminosilicate glasses.…”

“…Although homogeneous glass formation is generally difficult to achieve for binary alkaline earth silicates, a series of calorimetric measurements is available for the metasilicate stoichiometry, MSiO 3 , with M = Mg, 19 Ca, 20 Sr, and Ba. 21 Thanks to the recent availability of these data for heavy alkaline earths, our main goal will be to determine the influence of the size of the alkaline earth modifying cation on the boson peak and to compare it with that of the alkalis. Besides, the relationship between the temperatures of the boson peak and transverse sound velocities will be reviewed and the strongly anomalous case of SiO 2 and SiO 2 -rich glasses be pointed out.…”