Fabrication of lead-free semiconducting ceramics using a BaTiO3-(Bi1/2Na1/2)TiO3 system by adding CaO

Abstract

BaTiO 3 (Bi 1/2 Na 1/2 )TiO 3 (abbreviated as BTBNT) solid solution semiconducting ceramics, as a candidate for a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor usable over 130°C, were synthesized by adding CaO into the calcined powder. The CaO added BTBNT ceramics showed semiconducting behavior with the resistivity at room temperature µ RT = 10 3 ³ cm and a resistivity change near Curie temperature. Chemical composition analysis suggested that Ca 2+ acted as a donor by substituting for Na + in the BTBNT ceramics.

Origin of Semiconducting Behavior of CaO Added BaTiO₃-(Bi_1/2Na_1/2)TiO₃ Ceramics

“…Concerning the proc-A and -B samples, it is undoubted that Ca 2+ is incorporated into the perovskite crystal lattice, as reported in ref. [9]. It must be certain that Ca 2+ enters site of the BNT structure, because ionic size of Ca 2+ (1.34Å) is similar to Na + (1.39Å [11]).…”

“…. [9] reported that the BT-BNT semiconducting ceramics with 3.5mol% CaO addition were fabricated by sintering in an air atmosphere and showed also PTC behavior. They concluded that the Ca 2+ mainly entered into the site of O 3 perovskite structure and that Ca 2+ worked as a donor by substituting for Na + in the site.…”

“…Usually, 0.1 mol % of La 3+ or Nb 5+ addition works well as dopant for BT-based PTCR ceramics. However, more than 2 mol% of CaO was necessary to add into BT-BNT ceramics [9]. This means that doping mechanism and process of Ca 2+ should be understood for application.…”

“…One was that the CaO powder was added into the calcined powders such as reported in ref. [9] (process A: proc-A). The other was that the CaO powder was mixed with other raw material powders before calicination (process B: proc-B).…”

Ferroelectric photovoltaic tensor in visible-light-active Fe-doped BaTiO3single crystals

“…11,12) The widespread usage of MLCCs more or less relies on the defect chemistry [13][14][15][16][17][18][19][20][21] established for SrTiO 3 and BaTiO 3 . At present, intensive efforts [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] have been made to explore nanostructured materials and devices using BaTiO 3 -based materials, whereas the deep understanding of defects is far from complete for Pb(Zr, Ti)O 3 , [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] (Bi, Na)TiO 3 , [54][55][56][57]…”