I wouldn't have thought that expansion joints would be necessary with a tiled floor; a wooden floor, yes, as the wood will expand/contract with heat, but surely tiles don't.
I'd be interested in any view to the contrary, together with the rationale behind it.
I'm about to have tiles laid on top of underfloor heating in my house and I was told that we have to use flexible adhesive and we have bought BAL Admix which is flexible additive for the grout so the tiles can move with the heat.