Local Structure Evolution And Dipole-glass-like Relaxor Behavior For Bi(Mg_0.5Ti_0.5)O₃ Based Ceramics

Piezoelectric material is widely used in microelectronics,medical diagnostics and the automobile industry utilizing the piezoelectric effect which generates a voltage upon a mechanical strain,or vice versa.In order to extend Piezoelectric materials applicability to modern electronics,the information on local structure and physical properties are of great interest for fundamental studies.Among them,Bi?Mg0.5Ti0.5?O3 structural analogue of antiferroelectric PbZrO₃,which has attracted wide attention.However,Bi(Mg_0.5Ti_0.5)O₃presented in metastable state at normal temperature and pressure,and the form of solid solution is usually used to adjust the phase structure and electrical properties.In the solid solution system of?1-x?Bi(Mg_0.5Ti_0.5)O₃-xPbTiO₃,the morphotropic phase boundary?MPB?between tetragonal and rhombohedral phase,which exhibited enhanced piezoelectric activity?x=0.37?.The 0.5Ba_0.8Ca_0.2TiO₃-0.5Bi(Mg_0.5Ti_0.5)O₃ ferroelectric thin films demonstrates giant negative electrocaloric effects,ultrahigh thermal stability of dielectric permittivity and low dielectric loss.Despite much investigation,the local structure,phase evolution and electrical properties of these kinds of materials remain poorly understood.In this article,we selected Si,Zr doped 0.4Ba_0.8Ca_0.2Ti O₃-0.6Bi(Mg_0.5Ti_0.5)O₃ and?1-x?Bi(Mg_0.5Ti_0.5)O₃-xPbTiO₃ ceramics to be the study objects.The average/local structure,ferroelectric transition,dipole-glass-like relaxor behavior and re-entrant dipole-glass-like relaxor behavior of materials were investigated.The main result as follow:?1?In order to analysis the influence of oxgyen vacancy and Bi3+on the system structure and electrical properties,The 0.4Ba_0.8Ca_0.2TiO₃-0.6Bi(Mg_0.5Ti_0.5)O₃ and 5mol%Si doped0.4Ba_0.8Ca_0.2TiO₃-0.6Bi(Mg_0.5Ti_0.5)O₃ ceramics before and after annealing in oxygen were studied.All the samples show pseudo-cubic crystal structure;exhibit a typical re-entrant dipole-glass-like relaxor behavior and excellent thermal stability of dielectric permittivity above T_m.A statistical model was employed to describe the temperature dependence of dielectric permittivity,which reveals the interaction of dipole clusters.The large dielectric permittivity is attributed to the weakly interacting polar nanoregions?PNRs?associated with complex ionic substitution of both the A-site and B-site.The ultrahigh thermal stability is related to the thermal distribution of active dipoles.?2?In order to clearly study the ultrahigh thermal stability of dielectric permittivity,the0.6Bi(Mg_0.5Ti_0.5)O₃-0.4Ba_0.8Ca_0.2(Ti_0.875Zr_0.125)O₃ system according to in situ XRD,in situ Raman,TEM,and impedance spectroscopy.The ultrahigh thermal stability of permittivity is attributed to the weaker interaction between dipoles and less ferroelectric long-rang order.The dipole-glass-like relaxor nature of the 0.6BMT-0.4BZCT was characterized by polarization-electric field P?E?.The beta value obtained from isothermal modulus show two critical temperatures corresponding to the formation of PNRs and ferroelectric nanodomains in the relaxor.?3?The 0.65Bi(Mg_1/2Ti_1/2)O₃-0.35PbTiO₃ ceramic nearby MPB between tetragonal and rhombohedral was prepared.Dielectric permittivity dependence of temperature exhibits a re-entrance dipole glass-like behavior near room temperature.The behavior was described by the Vogel–Fulcher law and the new glass model.Furthermore,a phenomenological statistical model was employed to determine the distribution of clusters dependence of temperature.The lattice dynamics of the 0.65BMT-0.35PT ceramic was estimated by Raman spectroscopy from298 K to 723 K.A disruption of ferroelectric long-range order and an occurrence of local lattice distortion were revealed.The relaxor-ferroelectric?r-FE?nature of the 0.65BMT-0.35PT was characterized by polarization-electric field P?E?.A close relation between the the distribution of clusters and ferroelectric properties was established.?4?Furthermore,the effect of different Bi content on the re-entrant dipole-glass-like relaxor behavior of 0.6Bi_?1-x?(Mg_1/2Ti_1/2)O₃-0.4PbTiO₃ was studied.The two dielectric anomalies;?i?the low-temperature re-entrant relaxor transition and?ii?the high-temperature diffuse phase transition?DPT?can be understood by the phenomenological statistical model.The size of polar nanoregions?PNRs?in the two states was calculated.The dynamic of PNRs are analyzed using isothermal dielectric modulus,which shows three critical temperatures associated with the diffuse phase transition,the formation and freezing of PNRs.The temperature evolution of the PNRs evolution depends on the stoichiometry of bismuth.The results provide new insights into the dynamic behavior of PNRs and modification way of re-entrant relaxor behavior.