${}^{87}\mathrm{Sr}$ quadrupole perturbed NMR data of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ show that local symmetry breaking takes place also at the A site of the $\mathrm{AB}{\mathrm{O}}_3$ perovskite lattice in the cubic phase and not only at the B site as observed before. This is true for $\mathrm{Sr}{\mathrm{Ti}}^{16}{\mathrm{O}}_3$ (STO-16) and $\mathrm{Sr}{\mathrm{Ti}}^{18}{\mathrm{O}}_3$ (STO-18). The onset of the antiferrodistortive transition around $T_a=105\mathrm{K}$ is accompanied by a huge splitting of the ${}^{87}\mathrm{Sr}$ NMR line due to formation of macroscopic 90° domains and an anomalous shortening of the spin-spin relaxation time $T_2$ of the quadrupole satellite transitions which persist in the tetragonal phase down to $30\mathrm{K}$. This shows the presence of very low frequency fluctuations of the phase transition order parameter. Rhombohedral polar clusters appear in the tetragonal matrix both in STO-16 and STO-18 below $70\mathrm{K}$ and percolate in STO-18 below $T\approx 24\mathrm{K}$ leading to an inhomogeneous ferroelectric state. This is also supported by measurements of the field cooled ${}^{87}\mathrm{Sr}$ NMR spectra.

• Received 29 August 2005

DOI:https://doi.org/10.1103/PhysRevB.72.214117