Dielectric and piezoelectric anomalies around ferroelectric transition in Sr2Ta2O7

The dielectric constant and the piezoelectric resonance of Sr2Ta2O7 have been measured from 10 K to 300 K. The ferroelectric transition temperature Tc depends on samples. Piezoelectric resonance appears even in the paraelectric phase up to Tc + 30 K. The result means that there are polar regions above Tc. A mode associated with the ferroelectric phase transition softens toward Tc. The relation between ferroelectric properties and defects originated from twin and antiphase boundaries is discussed.