Submicron-structured (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT6) dense ceramics, from nanometric powder synthesized by sol gel auto-combustion at 500ºC and obtained by hot-pressing (800ºC-2h) and subsequent recrystallization at moderate temperature (1000-1050ºC-1h), have been studied. In-situ measurements at the shear mode of electromechanical resonance of non-standard thickness-poled shear plates as a function of the temperature show higher depolarization temperature than measurements at the radial mode of thin disks. Shear mode related material coefficients are measurable up to 160ºC, being k15?30% and d15?250 pC.N-1 at 130ºC. Depolarization is a complex phenomena caused by a ferroelectric (FE) macrodomains thermal randomization and a phase transition from the field-induced FE phase to a relaxor phase. The early stage of such a transition involves a non-negligible piezoelectricity arising most probably by the percolative coexistence of ferroelectric macrodomains in the resonator under the given stress field for each resonance mode.
Characterization of Nanostructured Phases and Peculiar Phase Transitions in BNBT Lead-Free Piezoceramics
E Mercadelli;C Galassi
2014
Abstract
Submicron-structured (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT6) dense ceramics, from nanometric powder synthesized by sol gel auto-combustion at 500ºC and obtained by hot-pressing (800ºC-2h) and subsequent recrystallization at moderate temperature (1000-1050ºC-1h), have been studied. In-situ measurements at the shear mode of electromechanical resonance of non-standard thickness-poled shear plates as a function of the temperature show higher depolarization temperature than measurements at the radial mode of thin disks. Shear mode related material coefficients are measurable up to 160ºC, being k15?30% and d15?250 pC.N-1 at 130ºC. Depolarization is a complex phenomena caused by a ferroelectric (FE) macrodomains thermal randomization and a phase transition from the field-induced FE phase to a relaxor phase. The early stage of such a transition involves a non-negligible piezoelectricity arising most probably by the percolative coexistence of ferroelectric macrodomains in the resonator under the given stress field for each resonance mode.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.