Effects of sintering temperature on structural, electrical and ferroelectric properties of La2Ti2O7 ceramics

Sintering characteristics of La2Ti2O7 prepared by solid state reaction method have been studied. Variations in the structural, electrical and ferroelectric properties are correlated with the changes in the physical and chemical microstructure occurring at different sintering temperatures. High sintering temperatures reduce the porosity; produce plate-like grain morphology with a large crystallite size, and a dense microstructure at 1600 degrees C with significant lattice strain. X-ray diffraction and vibrational spectroscopy confirm the formation of a well reacted La2Ti2O7 compound. Frequency dependent dielectric response epsilon' (f) in the range (10(-2)-10(6) Hz) shows significant dispersion for ceramics sintered at lower sintering temperatures (1200-1500 degrees C). Variations in the high frequency dielectric constant (epsilon') in the dispersion-free region at 1 MHz are found to correlate with the microstructural changes occurring at different sintering temperatures. Ceramics sintered at 1600 degrees C exhibit high resistivity (similar to 10(14) Omega cm), low dielectric loss (tan delta similar to 10(-2)-10(-3)), and a stable dielectric constant (epsilon'similar to 47) which remains dispersion-free in the entire frequency range (10(-2)-10(6) Hz). The high residual lattice strain in ceramics sintered at 1600 degrees C prevents reliable hysteresis loop measurements, whereas strain-free ceramics sintered at 1400-1500 degrees C exhibit hysteresis loops but the polarization values are low (0.34-0.37 mu C/cm(2)), coercive fields are high (50-67 kV/cm) and the piezoelectric coefficient d(33) = 1.0-1.5 pC/N is low.