Influence of aluminium inclusions on dielectric properties of three-phase PZT–cement–aluminium composites

Abstract

Novel three-phase piezoelectric composites that comprised lead zirconate titanate (PZT), aluminium and Portland cement were fabricated at a low poling voltage of 0·6 kV/mm and temperature of 160°C. Aluminium and PZT particles were distributed in a Portland cement matrix, and the dielectric constant, tan δ and strain coefficients were experimentally investigated as a function of inclusion volume fraction. The three-phase piezoelectric composites were found to possess higher piezoelectric strain coefficients, d33, than their two-phase counterparts (PZT and Portland cement composites). The highest value of d33 observed for the three-phase composite was 8·1 pC/N for volume fractions of 0·7 and 0·2 for PZT and aluminium respectively, which was 164% of the value observed for the two-phase composite, at the same PZT volume fraction. An analytical model was used to predict values for the effective dielectric constant of the three-phase composites, and these values compared reasonably well to the empirical data. An investigation of sample degradation as a function of time was performed. Samples showed the highest degree of reduced dielectric performance occurred within two days of data capture, and minimal subsequent reduction in performance after 300 d. Electrical properties of the composites are influenced by the oxidation of aluminium by the alkaline constituents in the cement matrix, distribution of PZT and aluminium within the matrix, particle agglomeration, inclusion size, contact resistance between particles and air voids. The increased dielectric and piezoelectric strain coefficients, demonstrate that these types of materials may be useful in applications such as structural health monitoring and energy harvesting.