Dysprosium doping on structural and electrical properties of lead free (Ba_0.7Ca_0.3)(Ti_0.92Sn_0.08)O₃ ceramic system

A series of Dy-doped (Ba_0.7Ca_0.3)(Ti_0.92Sn_0.08)O₃ (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 (ε_rt) = 2900, whereas on further increase of Dy content the ceramic system shows a drastic decrease in ε_rt value to ~ 885 for 2.5% concentration. Nearly frequency-independent behavior of ε_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.