Monte Carlo simulations based on a first-principles-derived Hamiltonian are conducted to study the properties of $\mathrm{P}\mathrm{b}({\mathrm{Z}\mathrm{r}}_{1-x}{\mathrm{T}\mathrm{i}}_x){\mathrm{O}}_3$ alloys compositionally modulated along the [100] pseudocubic direction near the morphotropic phase boundary. It is shown that compositional modulation causes the polarization to continuously rotate away from the modulation direction, resulting in the unexpected triclinic and $C$-type monoclinic ground states and huge enhancement of electromechanical responses (the peak of piezoelectric coefficient is as high as $30000\mathrm{p}\mathrm{C}/\mathrm{N}$). The orientation dependence of dipole-dipole interaction in modulated structure is revealed as the microscopic mechanism to be responsible for these anomalies.

• Received 21 February 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.067602