Microstructure and temperature dependence of properties of morphotropic phase boundary Bi(Mg_(1/2)Ti_(1/2))O_3-PbTiO_3 piezoceramics processed by conventional routes

摘要

Ceramics in the (1 - x)Bi(Mg_(1/2)Ti_(1/2))O_3-(x)PbTiO_3 system with x = 0.38,0.40 and 0.42 have been processed by conventional sintering from ceramic powders synthesised by one step, direct solid-state reaction of the constituent oxides at 900 deg C. Coexistence of rhombohedral and tetragonal phases was observed for the three compositions, in good agreement with the very recent report of a morphotropic phase boundary (MPB) in the system at x - 0.37. The microstructure was characterised, and dielectric properties as a function of temperature and frequency were studied. Permittivity presented two maxima with temperature at 300-400 deg C and approx 600 deg C. The dielectric anomalies were observed both on heating and cooling and showed hardly any dispersion. Therefore, they are most probably associated with phase transitions, the one at a higher temperature associated with the ferroelectric to paraelectric phase transition. Ceramics were poled and piezoelectric properties were studied, also as a function of temperature. Poling fields up to 5kVmm"' could be applied, and room temperature d_(33) values between 100 and 166pCN~(-1) were achieved, depending on composition and sintering temperature. Depoling was found to occur well below the Curie temperature, between 200 and 300 deg C, also depending on sintering temperature. This composition system seems promising for electromechanical transduction in the intermediate range of temperatures between 200 and 300 deg C and has the potential of reaching higher temperatures because of its Curie temperature at approx 600 deg C.