Critical behavior of the fluctuation heat capacity near the glass transition of metallic glasses

• Published in: Journal of non-crystalline solids Vol. 619; p. 122555
• Main Authors: Konchakov, R.A., Makarov, A.S., Afonin, G.V., Qiao, J.C., Vasin, M.G., Kobelev, N.P., Khonik, V.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2023
• Subjects: Critical indexes; Critical phenomena; Fluctuations; Glass transition; Heat capacity; Metallic glasses; Shear modulus; Glass transition; Metallic glasses; Fluctuations; Shear modulus; Heat capacity; Critical phenomena; Critical indexes
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2023.122555

The high-frequency shear modulus of five Zr-, Pd-, Cu-based conventional and two high-entropy bulk metallic glasses was measured in a wide temperature range up to the beginning of crystallization. Using these data and general thermodynamic relations, the “fluctuation” heat capacity ΔCf determined by local structural fluctuations in the defect regions is introduced and calculated. It is found that ΔCf temperature dependence for all metallic glasses has a large peak located slightly below or above the glass transition temperature but clearly lower than the crystallization onset temperature. The form of this peak resembles the characteristic λ-peak typical for order–disorder phase transitions. It is suggested that this ΔCf-peak reflects certain underlying critical phenomenon. The critical temperature T0 (peak temperature) and corresponding critical index α are determined. Averaged over all seven metallic glasses under investigation in the initial and relaxed states, the critical index <α>=0.26. The results obtained indicate that the fluctuations of thermal energy near the glass transition bear the marks of a continuous phase transition. However, the derived critical index is between those corresponding to a second-order phase transition (α≈0.1) and a critical transition characterized by a tricritical point (α≈0.5). •High-frequency shear modulus measurements of 7 metallic glasses are performed.•On this basis, defect-induced heat capacity jump near Tg is determined.•Fluctuation heat capacity is introduced and calculated.•Fluctuation heat capacity has a large peak near Tg.•This peak resembles characteristic peaks for order–disorder transitions.