Correlating the State and Properties of Grain Boundaries

Project Information

GB-CORRELATE

Grant agreement ID: 787446

DOI

10.3030/787446

Project closed

EC signature date 24 April 2018

Start date 1 August 2018

End date 31 July 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 500 000,00

EU contribution

€ 2 500 000,00

Coordinated by

MAX-PLANCK-INSTITUT FUR NACHHALTIGE MATERIALIEN GMBH
Germany

Periodic Reporting for period 4 - GB-CORRELATE (Correlating the State and Properties of Grain Boundaries)

Reporting period: 2023-02-01 to 2024-07-31

Summary of the context and overall objectives of the project

The project GB-CORRELATE dealt with one class of imperfections in materials - grain boundaries - which are of outmost importance for many applications, such as in high temperature materials, thermoelectric materials, conductors, catalysts or nanocrystalline materials. Crystalline materials are composed of a multitude of grains (each grain is a single crystal) separated by grain boundaries (GB). If grain size gets smaller and smaller - like in nanocrystalline materials - the GB volume can exceed several 10% of the total material volume and become most important for the resulting properties. The atomic coordination and chemistry of such grain boundaries may undergo phase transitions (also called “complexion” transitions), abrupt changes in structure and chemistry, which again will impact the material behavior - like strength, thermal stability, electrical resistance – even for conventional materials. However, this interplay between GB phases and material properties was at the start of GB-CORRELATE in its infancy and became world-wide an intense research area in the last years. Experimentally, GB are difficult to study - it needs atomic resolution and sensitivity with respect to chemistry. In addition, it was unknown under which temperature, stress (strain) or composition conditions phase transformations of GB occur. A fundamental understanding requires atomistic modelling connected with smart experiments.
The aim of the project was to develop a new understanding of GB in metals. Due to our systematic experimental studies down to the atomic scale interlinked with atomistic simulations, and property measurements we were able to make a big leap forward in understanding the origin and impact of GB phases and put the concepts to a new level. The breakthroughs we achieved relied on our well thought out thin film and bicrystal synthesis routes 1; they delivered a multitude of GB accessible to experimental studies by atomic resolved scanning transmission electron microscopy (S/TEM) techniques, which guided the search from an experimental perspective 2-6.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We found experimentally that GB in an elemental metal like Cu can undergo phase transitions as a consequence of strain (stress) 4, and temperature 2. These transitions reveal different atomic GB structures, GB excess volumes, etc., impacting properties. They are surprisingly frequent! Our atomistic simulations and experimental comparison between Cu and Al 6 revealed that fcc metals possess similar <111> tilt GB structures, which are a consequence of closest packing and bonding up to the second nearest neighbors 7. GB phase junctions are a new class of 1D defect separating two GB phases. In GB-CORRELATE we learned that GB phase junctions can have a limited mobility and they interact with their strain field to GB disconnections 2. We discovered that the atomic structure of “complexions” select the active disconnection mode. This can be important for shear-coupled GB motion 8 and grain growth.
We developed a new methodology to measure the electrical resistivity of single grain boundaries in thin films 9,10. A in-situ 4 point probe shuttle within the scanning electron microscope (SEM) was used and the voltage drop measured stepwise across the GB 9,10. We discovered that the excess volume is the main contributor to differences in resistivity of individual GB 10. Any trace impurity, will however, increase the electrical resistivity more strongly than changes in GB orientation parameters and atomic structure motifs 11. The developed workflow is useful for nanoelectronic devices with only few GB in metallizations. For thermoelectric materials a better knowledge of GB may help to improve the figure of merit –we made a step forward in this direction 12!
Our micro-mechanical experiments revealed that GB inclination 13,14 and chemistry 15 matter for dislocation-GB interactions and thus strength.
Our basic research results were communicated so far by more than 40 peer reviewed publications and led to 4 PhD thesis. The GB-CORRELATE team members have been actively presenting their research at workshops & conferences

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have found that GB phase transitions are a common phenomena 4,16-21. The packing density of GB atoms and the bonding interactions up to the second nearest neighbors determine the GB phase 21. Upon segregation, differences in structural units can occur: for Zr the structure motifs of a Cu GB get more distorted22, with decoration starting first at disconnections. In contrast, Ag modifies the Cu GB structure units and fills certain places first 23,24. Electrical resistivity of grain boundaries depends strongly on the excess volume as found for Cu tilt grain boundaries. Interestingly, dilute segregation (<0.4 at%) leads to a measurable change of GB resistivity as for the case of Cu containing trace levels of Fe, where an increase in GB resistivity by 1000% was found 25.
For the formation of disconnections, the structural units play an important role as they can exclude some Burgers vectors and step heights in case they don’t match with the repeat units of the structural GB motifs as found by atomistic simulations 19. The gained fundamental knowledge on GB atomistics is not only of academic interest, but has important consequences for grain growth, shear coupled GB motion and applications of metallization and conduction lines in semiconductor devices.


1. Malyar, N. V., et al., Materials Testing (2019) 61 (1), 5
2. Langenohl, L., et al., Nature Communications (2022) 13 (1), 3331
3. Meiners, T., et al., Acta Materialia (2020) 190, 93
4. Meiners, T., et al., Nature (2020) 579 (7799), 375
5. Peter, N. J., et al., Acta Materialia (2021) 214, 116960
6. Ahmad, S., et al., Acta Materialia (2024) 268, 119732
7. Brink, T., et al., Physical Review B (2023) 107 (5), 054103
8. Pemma, S., et al., Physical Review Materials (2024) 8 (6), 063602
9. Bishara, H., et al., ACS Applied Electronic Materials (2020) 2 (7), 2049
10. Bishara, H., et al., ACS nano (2021) 15 (10), 16607
11. Bishara, H., et al., Scripta Materialia (2023) 230, 115393
12. Luo, T., et al., Acta Materialia (2021) 217, 117147
13. Hosseinabadi, R., et al., Acta Materialia (2022) 230, 117841
14. Hosseinabadi, R., et al., Materials & Design (2023) 232, 112164
15. Bhat, M. K., et al., Acta Materialia (2023) 255, 119081
16. Langenohl, L., et al., Nat. Commun. (2022) 13, 3331
17. Ahmad, S., et al., Acta Mater. (2024) 268, 119732
18. Brink, T., et al., Phys. Rev. Mater. (2024) 8 (6), 063606
19. Pemma, S., et al., Phys. Rev. Mater. (2024) 8 (6), 063602
20. Ahmad, S., et al., Acta Mater. (2023) 243, 118499
21. Brink, T., et al., Phys. Rev. B (2023) 107, 054103
22. Meiners, T., et al., Acta Mater. (2020) 190, 93
23. Langenohl, L., et al., Phys. Rev. B (2023) 107 (13), 134112
24. Peter, N. J., et al., Acta Mater. (2021) 214, 116960
25. Bishara, H., et al., Scr. Mater. (2023) 230, 115393

Example of two different GB phases in a Cu <111> tilt GB