Nanometric Fluctuations of Sound Velocity in Alkali Borate Glasses and Fragility of Respective Melts

Abstract

The network structure of borate glass is remarkably modified by the addition of alkali metals. The alkali metal dependences of the first sharp diffraction peak (FSDP) and the boson peak (BP) are investigated in alkali borate glasses by elastic and inelastic neutron scattering experiments. With an increase in ionic radius of alkali ions, both the width ΔQ of FSDP and the BP energy decrease. The comparison of the characteristic length of medium‐range order (MRO) predicted by the FSDP and the position of the BP allows us to find the mean‐square fluctuations of the transverse sound velocity within series of alkali borate glasses. It is shown that the fragility of the respective alkali borate melts inversely correlates with the mean‐square fluctuations of the transverse sound velocity in glassy state.

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

“…The peak value Q fsdp corresponds to the real-space ordering with a periodicity of 2π/Q fsdp [5]. Figure 1a shows the static structure factor S(Q) of the single-alkali borate glasses, 0.22M 2 O-0.78B 2 O 3 (M = Li, Na, K, Rb, and Cs) measured by neutron scattering [6]. The FSDP and the second peak are denoted by Q 1 and Q 2 , respectively, in Figure 1a.…”