Ferroelectric and dielectric properties of Ca0.28Ba0.72Nb2O6 single crystals of tungsten bronzes structure

Abstract

Large Ca0.28Ba0.72Nb2O6 (CBN-28) single crystals exhibit saturated ferroelectric hysteresis loops under an electric field of 115kV∕cm along the [001] direction. Their spontaneous polarization, remanent polarization and coercive field are 35.3μC∕cm2, 32.2μC∕cm2, and 38.1kV∕cm, respectively. The dielectric constant and dielectric loss tanδ 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 °C at low frequencies, while the CBN-28 crystals experienced a first-order normal-relaxor ferroelectric phase transition around 252 °C on heating. A broad dielectric loss peak appears around 120 °C 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 °C).