Using multi-walled carbon nanotubes in spark plasma sintered Pb(Zr_0.47Ti_0.53)O₃ ceramics for tailoring dielectric and tunability properties

The addition of small amounts (below 0.1 wt. %) of multi-walled carbon nanotubes (MWCNTs) to Pb(Zr_0.47Ti_0.53)O₃ (PZT) ceramics prepared by spark plasma sintering is proposed as a method of tailoring the electrical properties, which are expected to be modified with respect to the pure PZT, both as result of the presence of 1-D conductive fillers in the ceramic product and via the microstructural modifications of ceramics induced during the sintering. The addition of even small amounts of carbon nanotubes strongly reduced the sinterability of PZT ceramics and resulted in the porous and fine-grained microstructures (relative density of 73% for a MWCNT addition of 0.5 vol. % by comparison with 91% in the pure PZT, produced in the same conditions). A monotonous decrease of permittivity with increasing the MWCNT level from ∼830 in pure PZT to ∼627 for x = 0.5 vol. %, at a fixed frequency f = 1kHz, and low dielectric losses below 2% have been observed. Tunability increases with respect to the values of dense PZT for small concentration of MWCNT as high as 0.0625 vol. % and then monotonically decreases for higher additions. Calculations by finite element modeling demonstrated that by addition of 1-D conductive fillers with compositions below the percolation limits to porous microstructures, the major role in changing the electrical properties via local field modification is related to the induced porosity rather than to the influence of the small amounts of MWCNTs survived after sintering and post-annealing treatment. The reduced permittivity with about 14% combined with low losses and higher tunability than in the pure PZT ceramics obtained at reasonable fields, makes the idea of using the addition of MWCNTs to ferroelectric ceramics an interesting approach in searching new structures for tunability properties.