Ferroelectric and dielectric properties of Ca_(0.28)Ba_(0.72)Nb_2O_6 single crystals of tungsten bronzes structure

摘要

Large Ca_(0.28)Ba_(0.72)Nb_2O_6 (CBN-28) single crystals exhibit saturated ferroelectric hysteresis loops under an electric field of 115 kV/cm along the [001] direction. Their spontaneous polarization, remanent polarization and coercive field are 35.3 μC/cm~2, 32.2 μC/cm~2, and 38.1 kV/cm, respectively. The dielectric constant and dielectric loss tan δ of the crystals are 195 and 0.32 at 10 kHz, respectively. A diffused dielectric anomaly with relaxor characteristic was observed in the range of 325-500℃ at low frequencies, while the CBN-28 crystals experienced a first-order normal-relaxor ferroelectric phase transition around 252℃ on heating. A broad dielectric loss peak appears around 120℃ and it is interpreted in terms of the migration of oxygen vacancies. The conductance activation energy was determined to be 1.33 eV in the high temperature regime (500-560℃).