Dielectric and Ferroelectric Properties of Ho2O3 Doped Barium Strontium Titanate Ceramicsq

The crystalline structure, surface morphology, dielectric and ferroelectric properties of 0~10wt% Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics prepared by conventional solid state method were studied using X-ray diffractometer, scanning electron microscopy, LCR measuring system and ferroelectric property test systems aiming for ceramic capacitor applications. It is found that proper amount of Ho2O3 can refine grains of the system. With the increase of Ho2O3 doping content, the average grain size of (Ba0.75Sr0.25) TiO3 ceramics decreases. When Ho2O3>8 wt%, (Ba0.75Sr0.25) TiO3 based ceramic samples are multi-phase compounds with typical perovskite structure accompanied by the appearance of cylindrical grains. The Ho3+ ions substitute the host A sites and B sites of (Ba0.75Sr0.25) TiO3 perovskite lattice, resulting in the lattice distortion of the system and the change of the relative dielectric constant and dielectric loss at room temperature. With the increase of Ho2O2 doping content, the relative dielectric constant at room temperature of the system increases first and then decreases. The maximum of relative dielectric constant at room temperature can be found in the 1 wt% Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics. When Ho2O3＞1 wt%, the maximum of relative dielectric constant ermax decreases and the temperature corresponding to the maximum of relative dielectric constant Tm shifts toward lower temperature with the increase of Ho2O3 doping content. The (Ba0.75Sr0.25) TiO3 ceramics with high Ho2O3 content show relaxor-like behavior which is characterized by the typical diffuse phase transition and frequency dispersion of dielectric constant. However, the (Ba0.75Sr0.25) TiO3 ceramics with low Ho2O3 content do not exhibit permittivity frequency dispersion. According to the P-E hysteresis loops of Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics, the ferroelectricity was increased and then decreased with the increase of Ho2O3 doping content. With the increase of Ho2O3 doping content, the P-E relationships turn out to be straight lines, implying the paraelectric phase for (Ba0.75Sr0.25) TiO3 ceramics with high Ho2O3 content.