Neutron scattering studies of static and dynamic correlation lengths in alkali metal borate glasses

Abstract This paper reports the variation in the first sharp diffraction peak (FSDP) and the boson peak (BP) of lithium and cesium borate glasses xM2O-(1-x)B2O3 (M = Li and Cs, x = 0.08. 0.14, and 0,22) investigated by elastic and inelastic neutron scattering. The different content dependences between lithium and cesium borate glasses are discussed on the basis of the different modifications of the boron-oxide network structure by the small Li and large Cs ions. The static characteristic correlation lengths Rfsdp were determined from the width of the FSDP of the static structure factor S(Q). The dynamic characteristic correlation lengths Rbp were determined from the BP energy of the dynamic structure factor S(E). They are close in absolute value (about 2 nm). With the increase in the alkali metal contents, Rfsdp increases, while Rbp gradually decreases with the different rate in the lithium and cesium glasses. However, their ratio, Rfsdp/Rbp increases with the content of the metal in both the lithium and cesium glasses at the same rate. The decrease in the amplitude of elastic fluctuations with the increasing x due to the increase in fragility with the increasing x might restore the correlation between Rfsdp and Rbp in the lithium borate glasses, and this tendency may be the same for the cesium borate glasses.