Cobalt ferrite sphere-coated buckhorn-like barium titanate: Fabrication, characterization, its dielectric resonance, and microwave attenuation properties

Barium titanate (BTO) with different morphology is prepared through hydrothermal method using titania spheres as precursor, then calcined at different temperatures and ultimately coated with cobalt ferrite (BTO/CFO). The dielectric dispersion of the composite containing BTO (75 wt.% ratio in paraffin wax) shows evidence of resonance behaviour in the microwave spectrum, rather than the usually observed relaxation mode. The imaginary part of permittivity (e '') displays a strong peak in the 10-13 GHz frequency region, especially for buckhorn-like BTO (hydrothermally synthesized at 110 degrees C and calcined at 1100 degrees C). The dielectric response anomaly of BTO in special morphology is due to the emission of plane acoustic waves caused by electrostrictive and converse piezoelectric effects. An accepted model is adopted to simulate the resonance frequency. The minimum reflection loss of cauliflower-like BTO (hydrothermally synthesized at 110 degrees C, then calcined at 600 degrees C for 2 h, 75 wt.% ratio) in paraffin wax reaches 30.831 dB at 10.56 GHz with a matching thickness of 2 mm, lower than all the reported values. When the sintering temperature is changed to 1100 degrees C (buckhorn-like BTO), the minimum reflection loss value is 24.37 dB at 12.56 GHz under the thickness of 3 mm. After combination with CFO, the value reaches 42.677 dB when the thickness is 5.6 mm. The ginger-like BTO (hydrothermally synthesized at 200 degrees C and calcined at different temperatures) is inferior in microwave reflection reduction. The electromagnetic interference shielding effectiveness of buckhorn-like BTO composite is calculated to be 12.7 dB (94.6% shielding) at resonance frequency (2 mm, 11.52 GHz). This work clearly shows the potential to tune the dielectric property of ferroelectrics through control of morphology, facilitating new comprehension of the ferroelectrics in microwave regime. (C) 2014 AIP Publishing LLC.