Sol–gel synthesis and characterisation of La doped (1−x)BaTiO₃–x(Bi_0·5K_0·5)TiO₃PTCR ceramics

Abstract

As a promising material for lead free positive temperature coefficient of resistivity (PTCR) ceramics, La doped (12x)BaTiO 3 -x(Bi 0?5 K 0?5 )TiO 3 [(12x)BT-xBKT] samples with 0#x#0?04 were prepared by a citrate-nitrate sol-gel method. The corresponding gels were heated at different temperatures (500, 600 and 800uC) to study the conditions necessary for the formation of the pure BT-BKT. Single phased perovskite powders with average particles size of 70 nm were obtained by heating the precursor gels at 800uC for 1 h in air. The crystal structure, microstructure and the electrical properties of La doped BT-BKT samples were studied. When the content of La was 0?2 mol.-%, the 0?99BT-0?01BKT ceramic showed the lowest r RT . With increasing addition of BKT, the Curie temperature (T c ) and the room temperature resistivity (r RT ) increased. When the content of BKT was 4 mol.-%, the sample sintered in air atmosphere still showed good PTCR behaviours with T c 5143uC, r RT 51?1610 4 V cm and lg (r max /r min )53?76.

Barium titanate-based thermistors: Past achievements, state of the art, and future perspectives

“…% when sintering in air. 257 As the (Bi 0.5 Na 0.5 )TiO 3 and (Bi 0.5 K 0.5 )TiO 3 phase content is increased, there is a concomitant increase in the Curie temperature. However, the room temperature resistivity also increases significantly.…”

“…These materials undergo a barium vacancy substitution by bismuth and sodium, and can be prepared by solid state and wet chemistry routes. 257 The Curie temperature of barium titanate can be increased further by incorporating a (Bi 0.5 K 0.5 )TiO 3 (BKT) phase, which has a T C equal to 360 C. [258][259][260][261][262] These compositions can be represented generically as BT-BMT, where M ¼ N-sodium or K-potassium. Usually, these materials are produced via a solid state reaction sintering route, although semi-oxalate synthesis can reduce sintering temperatures and, therefore, reduce evaporative losses of Na, K and Li from the crystal lattice.…”