  The effects of atomic short-range order on the properties of
Pb(Zr_{1-x}Ti_x)O_3 alloy in its morphotropic phase boundary (MPB) are
predicted by combining first-principles-based methods and annealing techniques.
Clustering is found to lead to a compositional expansion of this boundary,
while the association of unlike atoms yields a contraction of this region.
Atomic short-range order can thus drastically affect properties of perovskite
alloys in their MPB, by inducing phase transitions. Microscopic mechanisms
responsible for these effects are revealed and discussed.
