Effects of CaO addition on PTCR properties and room temperature resistance of Ho-doped (Ba,Sr)TiO3

摘要

Effects of Ca and Sr addition on the microstructure and positive temperature coefficient of resistance (PTCR) of Ho-doped BaTiO3 have been studied. The specimen was sintered in a reducing atmosphere (Po2<10??9 atm) at 1350?°C, followed by annealing processes at 1000?°C and Po2=1 atm. The lattice constants decreased with the addition of Sr (??15 mol%) or/and Ca (10 mol%). The substitution of Sr2+ for Ba sites in (Ba0.992??xSrxHo0.008)0.997TiO3 shifted Curie point (Tc) to lower temperatures by 3?°C/ mol% of SrO at x?? 0.15. The substitution of 10 mol% CaO for BaO in (Ba0.992??xSrx Ho0.008)0.997TiO3 caused a negligibly small shift in Tc and enhanced the dielectric constants at Tc. Higher room-temperature resistivities (??25) and larger temperature coefficients (??) were observed in (Ba0.992??xSrxHo0.008)0.997 TiO3. However, the addition of CaO effectively improved the microstructure of (Ba0.992??xSrxHo0.008)0.997TiO3 and lowered the room-temperature resistivity (??25) in the (Ba0.892??x Ca0.1SrxHo0.008)0.997TiO3 systems.