Dysprosium doping on structural and electrical properties of lead free (Ba_(0.7)Ca_(0.3))(Ti_(0.92)Sn_(0.08))O_3 ceramic system

摘要

A series of Dy-doped (Ba0.7Ca0.3)(Ti0.92Sn0.08)O-3 (BCST) ceramics in the concentration range of 0.0-2.5% Dy3+ was synthesized using conventional ceramic sintering route. XRD analysis confirms perovskite phase with a symmetry transition from disordered tetragonal phase at lower Dy content (x < 2.0%) to symmetric cubic phase at higher dopant content. Phase transformation and crystallographic changes observed are attributed to the substitution of Dy3+ ions at A-sites for x 1.5% and at B-sites for x > 1.5%. The ceramic with x = 2.5% Dy3+ possesses pseudo cubic structure with tetragonality (c/a) value of unity. Bimodal distribution of grains is observed in SEM micrographs of these ceramic samples. There is a clear transformation in grain shape from spherical to cubic with increasing Dy3+ content. Interestingly cubic grains are observed for 2.5% Dy3+ content in the BCST system which itself crystallizes in cubic phase at room temperature. Strengthened dielectric properties were observed up to 1.5% Dy3+ content with the room temperature dielectric constant (epsilon (rt) ) = 2900, whereas on further increase of Dy content the ceramic system shows a drastic decrease in epsilon (rt) value to similar to 885 for 2.5% concentration. Nearly frequency-independent behavior of epsilon (rt) is observed for all samples in the measured frequency range 100 kHz-1 MHz, with the property improving with increase in Dy content. Results on ferroelectric and piezoelectric properties of these ceramics are also presented in this paper.