Effects of Sr and Ca Addition on the Microstructure and the PTCR Properties of Ho-doped (Ba,Sr) TiO3

摘要

The effects of Ca and Sr addition on the microstructure and positive temperature coefficient of the resistance (PTCR) of Ho-doped BaTiO 3 have been Studied. The specimen was sintered in a reducing atmosphere (Po 2 < 10 -9 atm) at 1350 °C, followed by annealing at 1000'°C and Po 2 = 1 atm. The lattice constants decreased with the addition of Sr (<15 mol%) and/or Ca (10 mol%). The substitution of Sr2~+-aTT(_ti xOBS_ar3 _s xistHheisof tioenO.d 0( 0Bthsa)eo0 C9.9u92r7ie point to lower temperatures by 3 °C/ mol% of. SrO at x < 0.15. The substitution of 10 mol% CaO for Ba0 in (Bao.992-xCao.10SrrHo0.008)0.997TiO3 caused a negligibly small shift in the T_c and enhanced the dielectric constant at T_c. Higher room-temperature resistivities (pas) and larger temperature coefficients (a) were observed in (Bao.992-xSr1Hoo.008 )o.997TiO3. However, the addition of CaO effectively improved the microstructure of (Bao.292-Cao.10 Sr_xHou.00s)o.997TiOs and lowered the room-temperature resistivity (p25) in (Bao.s92-xCao.10Sr_xHo0.oos)o.997TiO3.