Dear Sang Hyun Ahn: I do not know your problem but I remember the weighing of La2O3 and the absorption of several species during it. This means an easy absorption. On the other hand, we know that the rare earth elements have mainly the valence three, a situation very different to that of the 3d elements which exhibit various possibilities. To understand this difference, we have to discuss the origin of the three valence of the rare earths. The two first valence states of the lanthanum have the same origin than the barium, element just before lanthanum. They are the result of the two 6s electrons appearing after the xenon. On the other hand the filling of the 4f shell starts after those of the 5s, 5p, 4d and 6s shells that is an amount of twenty electrons. Then it seems difficult to involve a 4f electron which is protected by all these electrons. It is for this reason that in the old text books, the additional electron appearing with the lanthanum is supposed to be a 5d electron and also for some other elements of the rare earths [1]. This hypothesis is now more or less forgotten but not fully. Considering the corpuscular model “The quantum state and periodicity” [2] an alternative approach is to suppose that it is the xenon shell, with its electrons gravitating in different directions of possible bonds, which leads to the third valence state of the Ln.

We know since about forty years than the xenon as some other gas call “inert” have valence properties [3-5]. As a result when with the lanthanum the atomic volume becomes of the order to that of the xenon, the lanthanum can exhibit at least one valence state of the xenon. Indeed its valence states are modified with the presence of the two 6s electrons, but one state can take place for example with one of the two 5s. This approach is corroborates with the high Tc superconductors as La2-xBaxCuO4 where the bivalent barium replace the trivalent lanthanum [6].

I hope that these short discussion will shed light on your work.

Kind Regards Xavier

[1]       Flahaut J., Les éléments des terres rares, Masson, (1959).

[2]       Oudet X., Ann. Fondation Louis de Brolgie, 36, 135-157, (2011). 

[3]       Barlett N., Proc. Chem. Soc., 218 (1962).

[4]       Classen H.H., Selig H. and Malm J.G., J. Amer. Chem Soc., 84, 3593, (1962).

[5]       Chernick C.L., Rec. Chem. Prog., 24, 139-155, (1962).

[6]       Mishra N.C. and Oudet X., Physica C, 465-469, (1993).

What is your lanthanum starting material?  My guess is that it is the chloride.  If you google hydrothermal synthesis ammonia, you will see quite few references of ammonia used, such as with TiCl4 to make anatase.   Clearly you will be liberating HCl so you should be able to conclude what role NH3 plays.

Add CTAB to lacl3 to add ammonia during the distillation of la2o3.