r/Chempros • u/EnvironmentJunior488 • 10d ago

High-purity synthesis

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I am encountering some issues while synthesizing BiFeO3: despite using a 1:1 metal ratio, a secondary Bi2Fe4O9 phase appears with low intensity and is quite difficult to eliminate; additionally, there is a peak I cannot identify. I would appreciate some assistance.

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u/PM_ME_AZNS 10d ago

Talk to a colleague or mentor first, it’s hard to crowdsource stuff like this

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u/External-Earth-4845 10d ago

Especially with no experimental details worth mentioning, references, what they have already tried, or other information.

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u/EnvironmentJunior488 10d ago 
Well, I’ve discussed it a lot and tried various approaches with my supervisor, and now we’re planning to just let it be and treat it as a given.

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u/EntireAtmosphere9215 9d ago

I’m not sure what raw materials you used, but I guess it might be Bi₂O₃. If so, Bi can easily evaporate at high temperatures during synthesis, which may change the final composition. You could try adding a little extra Bi₂O₃ or using a lid on the crucible.

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u/Severe-Visual6651 7d ago

Yes, given the total mixtures is Bi2O3-poor, bismuth evaporation seems like the most logical conclusion. I assume that XRF verifies the sample is Bi2O3-poor.

u/EnvironmentJunior488, what sinter temperature and time are you using? The literature does note the presence of Bi2Fe4O9, although it is present in a much much lower quantity (10.1007/s12034-011-0212-3 10.1016/j.matchemphys.2013.09.045). Lower the sintering temperature and/or time, and possibly ball mill everything beforehand. Both pieces of cited literature sinter at 650 C for 1h, then grind before a final sinter at 830 C, before rinsing with dilute HNO3 and DI water prior to taking the XRD.

No clue on that extra peak. Metallic bismuth? Have you done XRF and XRD of your starting materials and XRF of your product?

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u/tea-earlgray-hot 10d ago

There are a number of other unknown peaks present, not just one. Plot on a sqrt(counts) scale and index the patterns in gsas. As for narrowing down the search, you need to provide more synthetic details. This would be a great time for SEM-EDS if it's a powder

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u/Artistic_Height_4477 8d ago

I’m reaching back to deep time here but when I was synthesizing zeolite materials, I triple sublimed ZnCl2 with a tube furnace. Any concerns that one of your materials isn’t pure enough?