I would try ethylene glycol or glycerol. Because of the high viscosity (especially for glycerol), I would try them hot and then hope that the solute doesn't reprecipitate on cooling. If there is reprecipitation I would allow plenty of time for equilibration at the target temperature (presumably room temperature) before attempting separation by filtration or centrifugation.

Try N,N-Dimethylformamide (DMF).

Yurii V Geletii Thank you very much for the answer. Unfortunately, it did not resolve. Ethylene glycol or glycerol dissolves lithium tetraborate as the temperature increases.

I aim to coat any metal oxide surface with lithium tetraborate using the wet method. I will dissolve the lithium tetraborate in ethylene glycol and add the metal oxide. The ethylene glycol will evaporate as heated, and lithium tetraborate will crystallize onto the metal oxide surface. The coating process will then be performed with heat treatment at high temperature. Do you think this procedure is suitable for you?

Ali Yalçın If what you want is a uniform coating I think you'll have some difficulty with this method. (I don't have a better suggestion unfortunately.)

Most likely the glycol will evaporate quite slowly, allowing time for the tetraborate to form rather large, separate crystals rather than a coating. However, if the subsequent heating melts the tetraborate then you may achieve a uniform coating after all. Much depends on the interaction of the tetraborate with the metal oxide film, which may be in your favor.

Emanuel Cooper Thank you also for your feedback.

Kind regards

Emanuel Cooper I agree with you that "Most likely the glycol will evaporate quite slowly" The boiling point of ethylene glycol is about 200C.

I suggest to use a vacuum oven to evaporate the solvent.

Yurii V Geletii Thank you also for your feedback.

Kind regards