PHASE FORMATION, MICROSTRUCTURE AND ELECTRIC PROPERTIES OF La3+ SUBSTITUTION IN B-SITE OF LEAD-FREE BaTi0.91Sn0.09O3 CERAMICS

The study explored the influence of La³⁺ substitution at the B-site in BaTi0.91Sn0.09O3 (BTS) ceramics on their phase structure, microstructure, and electrical characteristics. La³⁺-doped BTS ceramics, denoted as Ba(Ti0.91Sn0.09)1-xLaxO3 (BTSL) with x = 0, 0.005, 0.010, 0.015, and 0.020, were synthesized via the conventional solid-state reaction method. The calcination and sintering processes were carried out at 1200°C for 2 hours and 1400–1450 °C for 4 hours, respectively. Results indicated that the undoped BTSL sample (x = 0) exhibited a pure perovskite phase without detectable impurities. However, when x ranged from 0.005 to 0.020, secondary impurity phases were observed alongside the perovskite structure. Phase analysis revealed that BTSL ceramics consisted of orthorhombic (O) and tetragonal (T) phases for x = 0–0.005, transitioned to a presence of O, T, and cubic (C) phases at x = 0.010–0.015, and exhibited only the C phase at x = 0.020. Rietveld refinement confirmed that La³⁺ occupied both A- and B-sites for compositions with x ≥ 0.005. As La³⁺ concentration increased, the average grain size and remnant polarization initially showed a slight reduction (x = 0 to 0.005) before significantly decreasing (x = 0.010 to 0.015). The Curie temperature (TC) was 43°C for x = 0, slightly increased to 44°C for x = 0.005, and then greatly decreased as x increased to 0.020.