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)O<inf>3</inf> ceramics, were explored for their structural, dielectric and piezoelectric properties. These modified ceramics with a composition of Pb<inf>0.76-3x/2</inf>Sm<inf>x</inf>Ca<inf>0.24</inf>Ti<inf>0.98</inf>Mn <inf>0.02</inf>O<inf>3</inf> (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 (ε′) 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<inf>C</inf> (determined from the plot of ε′ 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<inf>t</inf>/k<inf>p</inf>) was observed to increase from 11.7 (0 mol% Sm) to 27 (8 mol% Sm). Piezoelectric anisotropy (d<inf>33</inf>/d<inf>31</inf>) 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. © 2009 Elsevier B.V. All rights reserved. © 2010 Elsevier B.V., All rights reserved.