Morphotropic Phase Boundary Engineering in Ferroelectrics
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Barium calcium titanate (BCT), Sr-doped BCT (BSCT), and barium strontium calcium titanate-barium zirconate titanate xBSCT-(1-x)BZT (0.1&lex&le0.55) ceramics have been prepared by sol-gel method and solid state sintering process. The temperature dependences of dielectric constant and loss at different frequencies for all compositions were characterized and analyzed. For xBSCT-(1-x)BZT ceramics with 20% Ba in BCT substituted by Sr, the paraelectric-to-ferroelectric (cubic-to-tetragonal/rhombohedral) phase transition temperature T<sub>C</sub> increases for compositions of x<0.28, stays almost unchanged for x=0.28, and reduces significantly for x>0.28 with respect to the undoped xBCT-(1-x)BZT. Compared with BCT-BZT system, Sr-doped BSCT-BZT system shows a triple point at lower composition and temperature, and a morphotropic phase boundary (MPB) which is less vertical with respect to the composition axis in the phase diagram. Our results demonstrate that doping is an effective way to engineer MPB of BCT-BZT system and thus can help develop more compositions suitable for applications requiring large piezoelectric coefficient.