Slow Atomic Motion in Zr-Ti-Cu-Ni-Be Metallic Glasses Studied by NMR

Abstract

Nuclear magnetic resonance is used for the first time to detect slow atomic motion in metallic glasses, specifically, Be motion in Zr-Ti-Cu-Ni-Be bulk metallic glasses. The observations are not consistent with the vacancy-assisted and interstitial diffusion mechanisms and favor the spread-out free volume fluctuation mechanism for Be diffusion. Comparison with the results of Be diffusion measured by elastic backscattering the NMR results also indicates that the energy barriers for short-and long-range Be motion are the same. [S0031-9007 (98) The nature of atomic transport in metallic glasses has been the subject of numerous studies over the past decade and still remains a controversial and highly debated issue. Traditional techniques employed for diffusion study in metallic glasses include radioactive tracer [1,2], secondary ion mass spectrometry [3][4][5][6], and elastic backscattering (EBS) [7]. These techniques are based on the analysis of long-range diffusion and do not probe directly the characteristics of short-range atomic motions. For instance, possible spatial inhomogeneity of atomic motions cannot be probed directly by these techniques [1]. In contrast, nuclear magnetic resonance (NMR) is a direct probe of local atomic motions and has made significant contributions to the understanding of motions in polymeric and oxide glassy systems [8][9][10][11][12] and in crystalline metals and alloys [13][14][15][16]. So far, the potential of NMR has not been realized in studying atomic motions in metallic glasses [12].Recently, bulk metallic glasses Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 -Be 22.5 (vit1) and Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 (vit4) with extraordinarily high glass forming ability and thermal stability were discovered [17,18]. The Be diffusivity in both glasses was found by EBS to follow Arrhenius behavior below T g ͑ഠ625 K͒ with activation enthalpy of 1

Structural influence on atomic hopping and electronic states of Pd-based bulk metallic glasses

“…7,12 40 Ni 40 P 20 ͑S1͒ is larger than that in the Cucontaining samples by a factor of 1.31. Since the entire spectrum of S1 overlaps with that of S3 after frequency scaling, the line broadening is most likely due to the Knight shift distribution, predominantly anisotropic Knight shift distribution.…”

“…5 10 Be 27.5 ͑Vit4͒ BMGs was investigated and two beryllium diffusion mechanisms were identified: one involves single-atom hopping and the other involves the collective motion of groups of atoms. 6,7 It revealed that beryllium hopping is present in both the glassy and supercooled liquid states and the Arrhenius plot of the hopping rate follows a straight line across the glass transition temperature T g with no change of the activation energy. This demonstrates that the observed increase in the apparent activation energy of beryllium diffusion near T g arises simply from the stronger temperature dependence of the collective motion contribution as compared to that of single-atom hopping.…”

Li jump process inh−Li0.7TiS2studied by two-timeWilkening1, Heitjans2 2008Phys. Rev. B9881581View full textAdd to dashboardCite

“…[24][25][26] Quite recently, static SAE NMR spectroscopy was also applied to quadrupole nuclei with a spin-quantum number I of 3 / 2. First, Tang et al 20,56,57 recorded 9 Be NMR spin-alignment echoes to study ultraslow ionic motions in a metallic beryllium containing glass in order to reveal the prevailing diffusion mechanism in this material. The method was then used by Böhmer and co-workers 58,59 to investigate ultraslow Li motions in crystalline Li 3 68 It is worth mentioning in this context that 109 Ag stimulated echo NMR two-and four-time correlation functions were recorded recently to investigate silver dynamics in glasses of the compositions ͑AgI͒ x -͑AgPO 3 ͒ ͑1−x͒ , [69][70][71][72] 73 as well as in several other Ag compounds.…”

New prospects in studying Li diffusion—two-time stimulated echo NMR of spin-3/2 nuclei

“…The method has been applied before to detect ultraslow Be jumps in glasses [17][18][19] and also used to investigate Li diffusion in various crystalline ionic conductors [20][21][22][23][24][25]. However, a comprehensive comparison of 7 Li SAE-NMR results with data from 2D exchange NMR experiments and/or conventional relaxation NMR measurements, as presented here, is still missing.…”

“…In this way, for fixed evolution time t p and variable mixing time t m (10 µs t m 100 s), an ensemble averaged two-time single-particle correlation function S 2 (t m ) of the ion hopping process can be recorded [27], giving (in the ideal case) direct access to the jump rate τ −1 . In order to suppress the creation of dipolar contributions simultaneously with the generation of quadrupolar order, in the case of 7 Li SAE-NMR sufficiently short evolution times t p < 20 µs have to be used to record two-time correlation functions [21,22,19]. This is in contrast to stimulated echo NMR of 9 Be being subject to relatively weak dipolar interactions.…”