On the existence of Einstein oscillators and thermal conductivity in bulk metallic glass

Abstract

Low-temperature specific heat and thermal conductivity of bulk metallic glasses are measured to identify the primary vibrational modes associated with their unique structures. An Einstein-type localized vibrational mode with an Einstein temperature of 112 K is found in bulk metallic glass Ni 59.5 Nb 33.6 Sn 6.9 . This localized vibrational mode causes resonant scattering of phonons and results in the localization of phonons which leaves the phonon hopping conduction the limiting mechanism of thermal transport in bulk metallic glass Ni 59.5 Nb 33.6 Sn 6.9 at high temperature. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2234281͔The low-temperature specific heat and thermal conductivity of rapidly quenched metallic glasses had been the subjects of experimental investigations.1-3 Recently, bulk metallic glasses ͑BMGs͒ with a thickness of 1 mm or larger have been found in a number of alloy systems which usually contains three or more elements with large atomic size difference.4,5 BMGs differ from the rapidly quenched metallic glasses in the fact that a significantly slower cooling rate is required to get bulk glassy alloys. This is usually due to their strong viscosity-temperature dependence and the formation of polytetrahedral short range ordering ͑SRO͒ in undercooled alloy melts during cooling. 6 As a result, the phonon specific heat C phonon of metallic glass may not be described by the Debye model only and additional vibrational modes which are related with their unique SRO structures can exist. It is important to clarify the nature of these additional vibration modes since they not only modify the overall vibrational mode distribution but also influence the phonon thermal conductivity L of BMG. L is determined by the vibrational excitations and their mutual interactions. In this letter, we report on the existence of Einstein-type oscillators in a typical BMG and their influence on the phonon thermal conductivity.The metallic glass samples used in this study have the composition Ni 59.5 Nb 33.6 Sn 6.9 . Their synthesis and structural characterization were similar to those reported by Choi-Yim et al. 7 The specific heat measurements were carried out between 1.8 and 154 K with the heat capacity option of the physical property measurement system ͑PPMS͒ from Quantum Design. The relative error is estimated to be within 2% based on the instrument specifications. The electrical resistivity ͑͒ and thermal conductivity ͑͒ were measured from 5 to 300 K in a cryostat equipped with a copper radiation shield. We employed a longitudinal steady-state method and used Au-0.07 at. % Fe-Chromel thermocouples. The absolute accuracy of the measurement is limited to about ±5% by the uncertainty in the thermocouple junction separation.Magnetization measurements show that BMG Ni 59.5 Nb 33.6 Sn 6.9 is paramagnetic from 300 to 1.8 K with the susceptibility of 1.28ϫ 10 −6 emu/ ͑g Oe͒. There is no magnetic contribution to C P at zero magnetic field. Therefore, C P is the sum of two terms: electronic specific heat C electron and p...

Dilute magnetism and vibrational entropy inFe2Al5

“…Low-energy Einstein oscillator-type vibrational modes have been observed previously in metallic systems, 39,40 however the low-temperature specific heat observed here is not consistent with a single oscillator with a welldefined frequency. On the other hand the alternative explanation of a narrow electronic pseudogap, which could produce the low-temperature reduction in specific heat as observed here, seems unlikely since an extremely narrow gap would be required.…”

Boson Heat Capacity Peak in Metallic Glasses: Evidence of the Same Defect‐Induced Heat Absorption Mechanism in Structurally Relaxed and Partially Crystallized States

“…Granato suggested that interstitial defects behave as Einstein oscillators (the presence of such oscillators in MGs was repeatedly mentioned in the literature, e.g., Ref. ) and their low‐frequency vibration modes contribute to the heat capacity. The BP height is then expected to be linear in the defect concentration .…”

Thermal and Electrical Transport Properties of Zr-Based Bulk Metallic Glassy Alloys with High Glass-Forming Ability

“…1) Inoue et al have found that bulk metallic glassy (BMG) alloys can be obtained even by conventional casting techniques at relatively slow cooling rates, and have also reported that a number of metallic glasses can be formed by quenching in ZrCu, NiZr, PdCu alloy systems. 24) As summarized by Inoue, BMG alloys exhibit three common features as follows: (1) They mostly belong to multicomponent systems, (2) they have significant atomic size ratios of above 12%, and (3) they exhibit negative heats of mixing among the constituent elements. The satisfaction of these principles leads to a high glass transition temperature, T g and a low liquidus temperature.…”