Abstract
Abstract Lead calcium titanate ceramics modified by partial substitution of rare earths for lead, particularly, (Pb, Sm, Ca)(Ti, Mn)O 3 ceramics, were explored for their structural, dielectric and piezoelectric properties. These modified ceramics with a composition of Pb 0.76−3 x /2 Sm x Ca 0.24 Ti 0.98 Mn 0.02 O 3 ( 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 8 mol%, respectively. Microstructural study revealed the average grain size between 1.2 and 2.2 μm. The relative density was found to increase from 95% to 98.4% with increase in samarium substitution from 0 to 8 mol%, 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 (100 Hz to 1 MHz) and temperature (25–450 °C) range. The room temperature (25 °C) dielectric constant was found to increase from 130 (at 10 kHz) for pure lead calcium titanate sample to 380 (at 10 kHz) for 8 mol% samarium substituted sample and also showed a decreasing trend with increase in the frequency for all the substitutions (0–8 mol% 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 0–8 mol% Sm substitutions, respectively. Piezoelectric coefficients were also measured at room temperature. Electromechanical anisotropy ( k t / k p ) was observed to increase from 11.7 (0 mol% Sm) to 27 (8 mol% 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 8 mol% samarium. The experimental results successfully showed that samarium substitution not only reduces the lattice anisotropy but also helps in improving piezoelectric properties.
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