Boson peak and structural heterogeneity in ternary SiO 2 ‐Al 2 O 3 ‐B 2 O 3 glasses

We use low‐temperature heat capacity, low‐frequency Raman scattering, and THz time domain spectroscopy in order to scale the vibrational density of states and the Boson peak in SiO 2 ‐Al 2 O 3 ‐B 2 O 3 Yb‐laser host glasses. When substituting B 2 O 3 for SiO 2 at constant Al 2 O 3 dopant level, we find an optimal value for the ratio of B/Al in terms of mixture stability, at which the excess in the electron donor capability of Al 2 O 3 (relative to the SiO 2 backbone) is compensated by the more acidic B 2 O 3 . At this composition, Al 2 O 3 plays a mediating role in the structure of aluminoborosilicate glasses, facilitating dissolution of Yb 2 O 3 and admixture of B 2 O 3 into the SiO 2 network.