I am not good at this but I remember a discussion with
a very good chemist (Dr. F. B. d'Yvoire at University
of Paris XI - Orsay), he used some kind of sodium phosphate
(very stable, good crystalinity, large cubic unit cell...).
N Dragoe
--Nita DRAGOEhttp://www.hongo.ecc.u-tokyo.ac.jp/~tdragoe/personal.htm