Dear Sidarth, many thanks for asking this very interesting technical question on RG. Crystallization of yttrium nitrate hexahydrate is quite simple and straightforward. First of all make sure that you have a clear solution in water. If some turbidity persists, you can add a small amount of nitric acid to redissolve any insoluble material. It is no problem if the solution is slightly acidic. Then place the solution in a beaker (in the fume hood) and heat it to boiling on a hot plate while you stir it with a magnetic stirring bar to evaporate the water. As soon as the first solid material appears on the surface, stop heating, remove the stirring bar and let the solution cool to room temperature over night. This will lead to copious formation of crystals. You can isolate them by decanting the supernatant and dry them on filter paper. Further cooling of the supernatant solution to 0 °C can lead to an additional amount of crystals.

Good luck with your work and best wishes, Frank Edelmann

'Scratching' the side of the beaker with a glass rod is sometimes needed to initiate crystallisation

It should be straight forward by using a water bath and a magnetic stirrer. Make certain the solution is clear and it may help to add a couple drops of diluted nitric acid to prevent hydrolysis. Crystallization may lag behind sometimes, rub the inside wall of the beaker with a glass rod to initiate crystallization.

I am surprised you go ammonia emission!