Investigation of dielectric, electrical and optical properties of Pb0.5Sr0.5TiO3 ceramics

摘要

Pb0.5Sr0.5TiO3 (PST50) fine ceramic powders have been prepared by mechanosynthesis and mixed oxides methods. The dielectric, impedance, electric modulus, and ac conductivity have been carried out over a wide range of frequency and temperature i.e. 100 Hz-1 MHz and 100-650 K, respectively. PST50 shows low dielectric constant, very low dielectric loss, and diffused ferroelectric phase transition above room temperature. The low dielectric loss behavior was continued in the paraelectric region at higher frequencies. We observed only the bulk response using impedance spectroscopy and the two distinct electrical responses by modulus spectroscopy that were attributed to the grain effects (g) and grain boundary (gb) effects in the investigated temperature region. The Master modulus spectra indicated that the role of the grain boundary capacitance becomes more prominent with the increase in temperature. The temperature-dependent Raman spectroscopy revealed a soft mode behavior below the ferroelectric phase transition and breaking in the local symmetry in the paraelectric phase. In the paraelectric region, the local symmetry breaking was associated with the polar clusters localized at the grain boundaries. The frequency-dependent conductivity data were fitted in the modified power law, sigma(omega) = A(1)omega(n1) + A(2)omega(n2), and the results showed frequency dependent conduction below (450 K) and evidence of two types of conduction process at elevated temperatures i.e. the low-frequency conductivity (< 1kHz) is due to long-range ordering (frequency-independent) and high-frequency conduction due to the localized orientation hopping mechanism. The cross over frequency (hopping frequency) shifted towards the higher frequency side with an increase in temperature.