ion dynamics
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Author(s):  
Han Mingyue ◽  
Yang Luo ◽  
Liuhe Li ◽  
Hua Li ◽  
Ye Xu ◽  
...  

Abstract Investigating the ion dynamics in the emerging bipolar pulse high power impulse magnetron sputtering (BP-HiPIMS) discharge is necessary and important for broadening its industrial applications. Recently, an optimized plasma source operating the BP-HiPIMS with an auxiliary anode and a solenoidal coil is proposed to enhance the plasma flux and energy, named as ACBP-HiPIMS (‘A’-anode, ‘C’-coil). In the present work, the temporal evolutions of the ion velocity distribution functions (IVDF) in BP-HiPIMS and ACBP-HiPIMS discharges are measured using a retarding field energy analyser (RFEA). For the BP-HiPIMS discharge, operated at various positive pulse voltages U+, the temporal evolutions of IVDFs illustrate that there are two high-energy peaks, E1 and E2, which are both lower than the applied U+. The ratio of the mean ion energy Ei,mean to the applied U+ is around 0.55-0.6 at various U+. In ACBP-HiPIMS discharge, the IVDF evolution shows three distinguishable stages which has the similar evolution trend with the floating potential Vf on the RFEA frontplate: (i) the stable stage with two high-energy peaks (E2 and E3 with energy respectively lower and higher than the applied U+ amplitude) when the floating potential Vf is close to the applied positive pulse voltage; (ii) the transition stage with low-energy populations when the Vf drops by ~20 V within ~10 μs; and (iii) the oscillation stage with alternating E2 and E3 populations and ever-present E1 population when the Vf slighly descreases unitl to the end of positive pulse. The comparison of IVDFs in BP-HiPIMS and ACBP-HiPIMS suggests that both the mean ion energy and high-energy ion flux have been effectively improved in ACBP-HiPIMS discharge. The formation of floating potential drop is explored using the Langmuir probe which may be attributed to the establishment of anode double layer structure.


Author(s):  
S. Fatemi ◽  
A. R. Poppe ◽  
A. Vorburger ◽  
J. Lindkvist ◽  
M. Hamrin
Keyword(s):  

2021 ◽  
Author(s):  
Katharina Hogrefe ◽  
Lukas Schweiger ◽  
Bernhard Gadermaier ◽  
Jennifer L. M. Rupp ◽  
H. Martin R. Wilkening

Solid electrolytes with extraordinarily high Li-ionic conductivities are key for high performance all-solid-state batteries. So far, the thiophosphate Li10GeP2S12 (LGPS) belongs to the best Li ion conductors with an ionic conductivity exceeding 10 mS cm–1 at ambient. Recent molecular dynamics simulations performed by Dawson and Islam predict that the ionic conductivity of LGPS can be further enhanced by a factor of three if the crystallite size is reduced to the nanometer regime. A change in local ion coordination, hence local disorder, has been assumed to facilitate Li diffusion in the ab-plane of LGPS. As yet, no experimental evidence exists supporting this fascinating prediction. Here, we synthesized nanocrystalline LGPS by high-energy ball milling, characterized the material structurally and probed the Li+ ion transport parameters. Whereas X-ray powder diffraction and high-resolution 31P and 6Li magic angle spinning nuclear magnetic resonance (NMR) spectroscopy helped us to determine morphological changes and local structures upon milling, broadband conductivity spectroscopy in combination with electric modulus measurements allowed us to precisely follow the changes in Li+ ion dynamics. Surprisingly and against the behavior of other electrolytes, ionic conductivity turned out to decrease with increasing milling time, finally leading to a reduction of σ20°C by almost a factor of 10. This decrease affects both, bulk ion dynamics and total conductivity, which also comprises Li+ transport across grain boundary regions in LGPS. As could be shown by NMR, ball-milling leads to a structurally heterogeneous sample with the nm-sized LGPS crystallites being embedded in an amorphous matrix. This amorphous phase is responsible for the reduced performance of the milled electrolyte. Importantly, careful separation of the amorphous and (nano)crystalline contributions to the overall ionic conductivity revealed that even in the nanocrystalline regions Li+ ion dynamics is slowed down compared to untreated, coarse-grained LGPS. We conclude that defects introduced into the LGPS bulk structure via ball milling have a negative impact on ionic transport. We postulate that such kind of structural disorder is detrimental to fast ion transport in materials whose transport properties rely on crystallographically well-defined diffusion pathways.


Author(s):  
Vadim Khudiakov ◽  
Konstantin V Lotov ◽  
Mike Downer

Abstract In plasma wakefield accelerators, the wave excited in the plasma eventually breaks and leaves behind slowly changing fields and currents that perturb the ion density background. We study this process numerically using the example of a FACET experiment where the wave is excited by an electron bunch in the bubble regime in a radially bounded plasma. Four physical effects underlie the dynamics of ions: (1) attraction of ions toward the axis by the fields of the driver and the wave, resulting in formation of a density peak, (2) generation of ion-acoustic solitons following the decay of the density peak, (3) positive plasma charging after wave breaking, leading to acceleration of some ions in the radial direction, and (4) plasma pinching by the current generated during the wavebreaking. Interplay of these effects result in formation of various radial density profiles, which are difficult to produce in any other way.


Author(s):  
Andrey Zhuravlev ◽  
Karine Abgaryan ◽  
Dmitry Bazhanov ◽  
Dmitry Reviznikov

The work is devoted to Monte Carlo modeling of the formation / destruction of oxygen vacancies and the migration of oxygen ions in oxide layers of memristive elements.


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