Structural and dielectric behavior of Al-substituted CaCu_3Ti_4O_(12) ceramics with giant dielectric constant by spark plasma sintering

摘要

The influence of Al substitution on the structural and dielectric properties of CaCu_3Ti_(4-x)Al_xO_(12) (CCTAO, 0 ≤ x ≤ 0.09) has been investigated. CCTAO ceramics were prepared by spark plasma sintering (SPS) for 10 min at 975 ℃ of their precursor powders obtained by mechanochemical milling. X-ray diffraction and scanning electron microscopy revealed cubic crystal structure and an average grain size in the range -300-550 nm for the prepared ceramics. Though the smaller grain size of SPS CCTAO compared to previously reported grain sizes for CCTO-related ceramics prepared by solid state reaction, SPS CCTAO samples exhibited giant dielectric constant values in the range 10~3—10~4 at room temperature and 10 kHz. Complex impedance spectroscopy measurements revealed an electrically heterogeneous structure for the investigated ceramics. Three types of dielectric responses were detected in the modulus spectrum of the samples. These responses were attributed to grains, domain-boundaries (DBs) and grain-boundaries (GBs) interfaces. These results indicated that the giant dielectric constant of the SPS CCTAO ceramics is closely related to Maxwell-Wagner polarization at DBs and GBs.