Microstructure and electron properties of Sm modified lead calcium titanate ceramics

Abstract: Lead calcium titanate ceramics modified by partial substitution of rare earths for lead, particularly, (Pb, Sm, Ca)(Ti, Mn)O3 ceramics, were explored for their structural, dielectric and piezoelectric properties. These modified ceramics with a composition of Pb0.76−3x/2Sm x Ca0.24Ti0.98Mn0.02O3 (x =0−0.08) were prepared by solid state reaction route. The XRD study showed single-phase formation with tetragonal structure. Lattice anisotropy (c/a) was found to decrease from 1.057 to 1.023 with increase in Sm substitution from 0 to 8mol%, respectively. Microstructural study revealed the average grain size between 1.2 and 2.2μm. The relative density was found to increase from 95% to 98.4% with increase in samarium substitution from 0 to 8mol%, respectively. Detailed dilatometric study was performed in order to study the shrinkage behaviour during the sintering schedule. The maximum shrinkage was found to occur between 900°C and 1100°C. The dielectric constant (ɛ′) and loss (tan δ) for all the compositions were investigated over a wide frequency (100Hz to 1MHz) and temperature (25–450°C) range. The room temperature (25°C) dielectric constant was found to increase from 130 (at 10kHz) for pure lead calcium titanate sample to 380 (at 10kHz) for 8mol% samarium substituted sample and also showed a decreasing trend with increase in the frequency for all the substitutions (0–8mol% Sm). Curie temperature, T C (determined from the plot of ɛ′ vs. temperature) and tan δ were found to decrease with increasing samarium content. The Curie temperature was found to decrease from 348°C to 192°C for 0–8mol% Sm substitutions, respectively. Piezoelectric coefficients were also measured at room temperature. Electromechanical anisotropy (k t/k p) was observed to increase from 11.7 (0mol% Sm) to 27 (8mol% Sm). Piezoelectric anisotropy (d 33/d 31) was also observed to increase from 22.5 for un-substituted sample to 28 for the sample substituted with 8mol% samarium. The experimental results successfully showed that samarium substitution not only reduces the lattice anisotropy but also helps in improving piezoelectric properties. [Copyright &y& Elsevier]