The Depolarization Behavior Of PbZrO₃-Based Ferroelectric Ceramics Under Hydrostatic Pressure

Ferroelectric high pulse power exhibits important applications in many new high-tech fields such as national defense and aerospace.The main working principle is based on the shock induced depolarization of ferroelectric materials.To be detailed,the material is initially located at the boundary between ferroelectric and antiferroelectric phase,many electric charges appeared at both surfaces when it is poled to become a ferroelectric material.And the electric charges can be released instantaneously when a shock wave is applied.Because of the large remnant polarization,rich phase structures and low-stress-induced phase transition depolarization process,the Pb(Zr_0.95Ti_0.05)O₃（PZT95/5）ferroelectric ceramics are the most popular material for ferroelectric pulse power.The greatest technical challenge now in practical applications is that the PZT95/5ceramics experience a phase transition from a low-temperature rhombohedral ferroelectric phase to high-temperature rhombohedral ferroelectric phase(F_R（LT）-F_R（HT）)at around 45℃upon heating and the P_r declines about 10%under this phase transition,which leads to a sharp drop in energy storage density according to the formula u=P_r²/2ε_rε0.Owing to the operation temperature of ferroelectric pulse power is from-55 to 125℃the phase transition largely impacts the temperature stability of PZT95/5ferroelectric ceramics.Seeing from the perovskite ferroelectric ceramic crystal structure,it is important to design and regulate the F_R（LT）-F_R（HT）phase boundary to eliminate the F_R（LT）-F_R（HT）phase boundary or change the phase transition series.Moreover,the effects of components,pores and external loads on depolarization process have been studied for decades,but the grain size effect under hydrostatic pressure has not been discussed systematically.In order to obtain a material that does not excit F_R（LT）-F_R（HT）phase transition as well as locates at ferroelectric-antiferroelectric phase boundary,we have designed and prepared the（1-x）PZ-xBMN ferroelectric ceramic material,where the lead zirconate（PbZrO₃,PZ）is an orthorhombic antiferroelectric material and the barium magnesium niobate is a hexagonal microwave dielectric material.The value of x in our experiment are 0.02,0.03,0.04 and 0.05.The microstructures and P-E hysteresis loops indicate that the material changes from antiferroelectric phase to ferroelectric,and then the relaxor ferroelectric at last with increasing of BMN content.Especially,the 0.97PZ-0.03BMN ceramic is located at ferroelectric-antiferroelectric phase boundary and the P_r is32.4μC/cm² under 4.5kV/mm.The in-situ hydrostatic pressure induced depolarization experiment found that the 0.97PZ-0.03BMN ceramics begin to depolarize at a low pressure of 200MPa and depolarize 90%of initial remnant polarization at 230MPa.This pressure driven depolarization should be attributed to the pressure induced ferroelectric-antiferroelectric（FE-AFE）phase transition,supported by the emergence of double P-E loops at higher electric fields and hydrostatic pressures.The reciprocal dielectric constant decreases linearly as temperature increases from room temperature to 195℃,which indicates no thermal-induced phase transitions take place during this temperature range.The P-E loops recorded under different temperatures show that the P_r almost keeps unchanged in wide temperature range,indicating that the temperature stability of P_r in 0.97PZ-0.03BMN is always prior than PZT95/5 ceramics.The 0.97PZ-0.03BMN ceramics exhibit not only a FE-AFE phase transition depolarization under stress but also a great temperature stability in wide temperature range.Therefore,it may replace the PZT95/5 ceramics to become a new generation of ferroelectric high pulse power material.And the depolarization behavior of PZT95/5 with different grain sizes under hydrostatic pressure was studied in this paper.It is found that the initial phase transition pressure increases at first and then decreases with increasing grain size.The initial depolarization pressure reaches to maximum value at the grain size of 7.91μm and the depolarization coefficient has a maximum value.