Structural and electrical properties of Ba 5− xCa xSmTi 3Nb 7O 30 ( x = 0–5) ferroelectric ceramics

Abstract

Samples of the compositions Ba 5− x Ca x SmTi 3Nb 7O 30 ( x = 0–5), where Ba has been replaced by Ca in steps, were synthesized by solid state reaction method and studied for their structural, dielectric and electrical properties. X-ray diffraction analysis shows the formation of the compounds in an orthorhombic structure at room temperature. Scanning electron micrographs reveal that the average grain size of the compounds increases with increase in calcium content. Detailed studies of dielectric properties as a function of temperature at different frequencies suggest that the synthesized compounds undergo non-relaxor type ferroelectric–paraelectric phase transition of diffuse nature with a decrease in the value of dielectric constant as calcium content increases. When barium is completely replaced by calcium (i.e., Ca 5SmTi 3Nb 7O 30), the compound does not show any phase transition. The ferroelectric nature of the studied compounds was confirmed by recording the polarization–electric field ( P– E) hysteresis loops at room temperature. The remanent polarization value is observed to be highest in the sample with x = 1. The temperature variation of P– E loop in the Ca free compound has been reported. The dc and ac conductivity study over a wide temperature range suggests that the compounds have negative temperature coefficient of resistance (NTCR) behaviour.