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Jun 23, 2021 10 tweets 3 min read Read on X
After our initial work on Li2MnO3, we discovered that there was a debate in the literature for a related compound. The more promising Li1.2Mn0.54Ni0.13Co0.13O2. It is the Li and Mn rich analogue to the Li[NiMnCo]O2 oxides used in commercial batteries.
What was this debate? It was whether the material existed as a solid solution or if it was an intergrowth or mix of Li2MnO3 and Li[NiMnCo]O2. Ie, if the composition crystallised as one or two phases. Here is an excerpt highlighting the debate pubs.acs.org/doi/10.1021/cm…
And here is what the two proposed models are. In the multi-phase model the hexagonal ordering occurs exclusively for Li and Mn whereas in the single phase Li in the transition metal layer can also have Ni and Co as nearest neighbours.
Why does this matter? It has been argued that the additional capacity, specifically the anionic redox capacity, originated from the Li2MnO3 phase. Thus, its presence is necessary for that additional capacity.
So why is this so difficult? Surely a diffraction experiment can tell you whether multiple phases are present. Lets play a game of spot the difference🙂. Below are diffraction patterns (X-rays and neutrons) from a confirmed "single" and "multi" phase samples
Aside from intensity differences in the neutron diffraction pattern, they look pretty similar. Figuring out this puzzle is further complicated since the compound has disorder over several length scales. Short to long: Atomic site mixing, stacking faults and phase segregation
Disorder over multiple length scales means to answer this question multiple characterisation tools are needed. This is what we did, looking at both local and long range information. The methods were diffraction, raman spectroscopy, magnetic susceptibility, and STEM measurements
What did we learn? Is the material one or two phases?? The answer is: both and it depends on how you synthesise the material. Similar to the first paper, solid state gives an inhomogeneous distribution of elements whereas the sol gel method is more homogeneous
It is not too surprising that this has led to conflicting results over the years. It does raise some interesting ideas about tailoring phase intergrowth via different synthetic pathways however.
The full story can be found here: pubs.acs.org/doi/10.1021/ac…

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More from @RealSci_Nano

Aug 15, 2023
Today we’ll refresh our knowledge of some of the battery terms. Let’s start from the beginning: we call a battery a device that converts chemical into electric energy using redox reactions. To narrow it down, let’s focus on batteries which use Li (Li-ion batteries).
image:iStock Image
It is a secondary (rechargeable) battery which uses reversible reactions with Li-ion to store energy.
fig: https://t.co/P4WUqJLAp4ul.org
Image
Redox (oxidation-reduction) reactions involve transfer of electrons between two substances. As a result of gaining or losing electron, oxidation state of the substances changes.
Read 13 tweets
Nov 6, 2022
I still don't know what kind of job I want to do after I finish my PhD.

But at least I found the answer to what kind of job I do not want:

I don't want a bullshit job!

(and they are way more common than we want to admit, even among "blue-collar" jobs.

en.wikipedia.org/wiki/Bullshit_…
BS job="a form of paid employment that is so completely pointless, unnecessary, or pernicious that even the employee cannot justify its existence even though, as part of the conditions of employment, the employee feels obliged to pretend that this is not the case."
I promised that I would talk about career opportunities after the PhD and other @AltAcChats using a university-organized event that I attended this week.

Well, I was recommended not to, sorry!

However, this book (50% read atm) is helping me clarify that.
Read 5 tweets
Nov 6, 2022
Imagine that you design the perfect cake. Due to the combination of different layers of ingredients, it will have awesome unrealistic properties. A #meta cake!

But: will the structure withstand the temperatures needed during baking?

Thread on my paper 👇
onlinelibrary.wiley.com/doi/10.1002/ad… https://www.epicurious.com/expert-advice/how-to-fix-a-broken
Instead of a cake, we designed a near-perfect absorber.

Less than 0.1% of the light hitting it can escape it!

How is that possible? By disorder!

Turns out that having the layers of ingredients intermix a bit makes an even better cake!

1st lesson: it's not always worth it to find a fabrication technique that avoids intermixing.

Those techniques are way slower and don't necessarily improve their properties.

A step towards scalable, large-area #metamaterials.

Read 14 tweets
Nov 6, 2022
If you have been folowing the account his week, you might have guessed that I have a thing for definitions and debates over definitions.

What is a metal?



What is a metamaterial?



And now: what is a cake?

That is the discussion that delayed our lab's (@LNM_eth) baking competitions.

Do cakes need to be sweet?

Are all cakes flour based?

Are all cakes layered?

Are all cakes round?

(and much more)
Maybe the reason for this discussion is that we discussed it in Switzerland, a country known for its polyglotism:

Turns out that @Wikipedia defines it differently in different languages!

In French, for example, salty cakes pass the filter:

fr.wikipedia.org/wiki/G%C3%A2te…
Read 6 tweets
Nov 4, 2022
On Wednesday I tried to define a #metamaterial.

Now it's time to define #metals, which should be way easier, right?

Spoiler: even in a #metallurgy group @LNM_eth, not everyone agrees!

First a list of "high-school science" definitions that don't really help us. The

"Metals are reflective": Yes but not all reflective things are metals. Not definition friendly. Image
"Metals are ductile and malleable, easy to work with": Not necessarily. Good luck working with Tungsten, which is definitely metal.

This article tells a bit about how hard making the Tungsten filaments that we used on lights was!

americanscientist.org/article/tungst…
Read 16 tweets
Oct 6, 2022
Finally, the thread (you didn't know) you have been waiting for 🥳 "How can we use X-ray scattering to learn about the way the atoms sit in a #small #nanoparticle?" - lets use the Pair Distribution Function #PDF ! It's all about the neighbors 1/6 /@RPittkowski
To get information from small #nanoparticles, where periodic lattice planes are rare, we measure the X-ray scattering to very large scattering angles. This is called #Xray #totalscattering. So we need to come veeeery close with the detector to our sample.😱😬 2/6
Again, we integrate our scattering image (check up older tweets), but we are not done yet. More data treatment is necessary. We use a #Fouriertransform and transform from reciprocal (Q) space to #real #space - and there we have it, our PDF 😍3/6
Read 6 tweets

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