[en] Polar tweed was discovered in mechanically stressed LaAlO3. Local patches of strained material (diameter ca. 5 mu m) form interwoven patterns seen in birefringence images, Piezo-Force Microscopy (PFM) and Resonant Piezoelectric Spectroscopy (RPS). PFM and RPS observations prove unequivocally that electrical polarity exists inside the tweed patterns of LaAlO3. The local piezoelectric effect varies greatly within the tweed patterns and reaches magnitudes similar to quartz. The patterns were mapped by the shift of the E-g soft-mode frequency by Raman spectroscopy.
