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We performed parallel measurements of the high-frequency shear modulus $G$ and relative volume $\Delta V/V$ for high-entropy Ti$_{20}$Zr$_{20}$Hf$_{20}$Be$_{20}$Cu$_{20}$ and Ti$_{20}$Zr$_{20}$Hf$_{20}$Be$_{20}$Ni$_{20}$ glasses upon heating from room temperature up to the complete crystallization. The changes of these properties due to structural relaxation both below and above the glass transition temperature are singled out. It is shown that these changes for both initial and preannealed samples can be well described within the framework of the Interstitialcy theory. It is found that the whole relaxation process in the full temperature range of the experiments for both samples' states can be characterized by a single dimensionless temperature-independent parameter $K_i=dln\;G/dln\;V$, which equals to -44 and -53 for the above glasses, respectively, and strongly points at interstitial-type defects as a source of relaxation. We also show that the relaxation of the relative volume linearly depends on the defect concentration. This behavior can be described by another dimensionless temperature-independent parameter, which is related with the relaxation volume of defects. Possible contribution of vacancy-like defects into the relaxation is discussed., Comment: 15 pages, 5 figures

We performed high-frequency (0.4 to 1.7 MHz) measurements of the internal friction (IF) on 14 bulk metallic glasses (MGs). It is found that 12 of these MGs display relaxation IF peaks at temperatures T= 400-500 K, which are weakly affected by heat treatment within the amorphous state. The corresponding relaxation time is about 0.3 microseconds. This fast relaxation is reported for the first time in the literature. The apparent activation enthalpy for 4 MGs is determined., Comment: 15 pages, 4 figures

We performed calorimetric measurements on 30 bulk metallic glasses differing with their mixing entropies DSmix. On this basis, the excess entropies DS and excess enthalpies DH of glasses with respect to their maternal crystalline states are calculated. It is found that the excess entropy DS on the average decreases with increasing mixing entropy DSmix. This means that so-called "high-entropymetallic glasses" (i.e. the glasses having high DSmix) actually constitute glasses with low excess entropy DS. We predict that such glasses should have reduced relaxation ability. We also found that the excess enthalpy DH of glass linearly increases with its excess entropy DS, in line with a general thermodynamic estimate., Comment: 5 pages, 3 figures

We measured the shear viscosity of 14 metallic glasses differing with their mixing entropy $\Delta S_{mix}$. It is found that the viscosity at the glass transition temperature $T_g$ significantly increases with $\Delta S_{mix}$. Using calorimetric data, we calculated the excess entropy of all glasses $\Delta S$ with respect to their maternal crystalline states as a function of temperature. It is shown that the excess entropy $\Delta S$ both at room temperature and at $T_g$ \textit{decreases} with $\Delta S_{mix}$. It is concluded that glasses with "high mixing entropy" $\Delta S_{mix}$ correspond to MGs with \textit{low} excess entropy $\Delta S$. The origin of the increased shear viscosity at $T_g$ of glasses with high $\Delta S_{mix}$ is determined by their reduced excess entropy $\Delta S$., Comment: 12 pages, 4 Figures

Using a notion on the excess entropy of glass with respect to the counterpart crystal, we introduce a simple dimensionless order parameter $\xi$, which changes from $\xi \rightarrow 0$ to $\xi \rightarrow 1$. The former case corresponds to a strongly disordered liquid-like structure while the latter situation describes a highly ordered crystal-like glass. This approach is applied to 13 metallic and 2 tellurite glasses. We found that $\xi$ is strongly sensitive to structural state and/or chemical composition. It can be also used for a comparison of the order in glasses belonging to different classes and appear to represent a new way of structural analysis., Comment: 5 pages, 5 figures

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 $\Delta C_f$ determined by local structural fluctuations in the defect regions is introduced and calculated. It is found that $\Delta C_f$ 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 $\lambda$-peak typical for order-disorder phase transitions. It is suggested that this $\Delta C_f$-peak reflects certain underlying critical phenomenon. The critical temperature $T_0$ (peak temperature) and corresponding critical index $\alpha$ are determined. Averaged over all seven metallic glasses under investigation in the initial and relaxed states, the critical index $\alpha=0.26$. 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 ($\alpha\approx 0.1$) and a critical transition characterized by a tricritical point ($\alpha \approx 0.5$)., Comment: 18 pages, 4 figures

On the basis of shear modulus measurements on a Pt-based glass, we calculated temperature dependence of the defect concentration c using the Interstitialcy theory. This temperature dependence is compared with temperature dependence of the normalized full width at half maximum (FWHM) gamma of the first peak of the structure factor S(q) for the same glass available in the literature. It is found that above the glass transition temperature Tg linearly increases with c in the same way for both initial and relaxed (preannealed) samples providing the evidence of defect-induced disordering in the supercooled liquid region independent of glass thermal prehistory. For both states of the samples, the derivative d(gamma)/dc is close to unity. Below Tg, the interrelation between gamma and c is entirely different for initial and relaxed samples. In the former case, strong defect-induced ordering upon approaching Tg is observed while relaxed samples do not reveal any clear ordering/disordering. Possible reasons for these observations are discussed. To further investigate the relationship between the normalized FWHM and defect concentration, we performed molecular dynamic simulation of gamma(c)-dependence in a high-entropy FeNiCrCoCu model glass. It is found that gamma also linearly increases with c while the derivative d(gamma)/dc is again close to unity just as in the case of Pt-based glass., Comment: 15 pages, 6 postscript figures