Different orders for a phase transition (variable depending)

1. Apr 6, 2015

lfqm

Hi guys!
I've got this system in which Eherenfest classification of "order" is assumed to be ok.
So I took my free energy function $$G(T,P)$$ and start differentiating.
I found just one phase transition between two phases, the problem is the phase transition is of different order depending on the variable, i.e. the lowest derivative respect to T to be discontinuous is the first, but the lowest derivative respect to P to be discontinuous is the second...

So... Is this normal?, I though it didn't matter how I cross the boundary between the phases, but apparently it does.
What is the order if the transition?, first (it is the lowest)?

Thanks

2. Apr 11, 2015