Hengchang Nie

Three-stage evolution of dynamic hysteresis scaling behavior in 63PbTiO3−37BiScO3 bulk ceramics

The ferroelectric hysteresis loops of 63PbTiO3−37BiScO3 ceramics were measured under sinusoidal electric fields in the range of frequency from 0.1 to 100 Hz and field from 5 to 55 kV/cm. The fitting results showed two linear relations existed between the logarithm of hysteresis area ⟨A⟩ and the logarithm of the amplitude of field E0 in the first and third field region. In the second region, no linear relation existed due to polarization reversal. These three-stage behaviors were distinct from the existing two-stage behaviors. The slopes in the third stage increase with the increasing of frequency, which can be attributed to dielectric loss under high frequency.

Temperature scaling of dynamic hysteresis in Zr-rich PbZr1−xTixO3 ceramics

The temperature scaling relations of the dynamic hysteresis were investigated in Zr-rich lead zirconate titanate (PZT) bulk ceramics. At each relation curve, there is a discontinuous district corresponding to the low- and high-temperature phase transitions. The temperatures are divided into low-T region and high-T region. At each temperature region, three power-law scaling relations were obtained for hysteresis area ⟨A⟩, coercivity Ec, and remnant polarization Pr with T, respectively. The six temperature scaling relations are field dependent and the simplified forms are different from the results obtained from the soft and hard PZT ceramics.

Pressure driven depolarization behavior of Bi0.5Na0.5TiO3 based lead-free ceramics

Pressure driven depolarization behavior has been widely investigated for its scientific significance and practical applications. However, previous related studies were all based on lead-containing ferroelectric (FE) materials leading to detrimental environmental concerns. In the present work, we report the pressure driven depolarization behavior in Bi-based lead-free 0.97[(1-x)Bi0.5Na0.5TiO3-xBiAlO3)]-0.03K0.5Na0.5NbO3 (BNT-x) ceramics. Particularly, with increasing hydrostatic pressure from 0 MPa to 495 MPa, the remanent polarization of BNT-0.04 decreases from 30.7 μC/cm2 to 8.2 μC/cm2, reducing ∼73% of its initial value. The observed depolarization phenomenon is associated with the pressure induced polar FE-nonpolar relaxor phase transition. The results reveal BNT based ceramics as promising lead free candidates for mechanical-electrical energy conversion applications based on the pressure driven depolarization behavior.

Temperature dependences of dynamic hysteresis in Pb(Zr,Sn,Ti)O3 ceramics extending over Curie temperature

Dynamic hysteresis of Nb-doped Pb(Zr,Sn,Ti)O3 ferroelectric ceramics with the first-order phase transition was investigated in a wide temperature (T) range from 293 K to 433 K, which extended over its Curie temperature (Tc = 422 K) and another transition temperature (T0 = 413 K). Three linear scaling relations were obtained when the working fields E0 were over 1.5 times of coercive field Ec, where the well-saturated loops occurred. The highest applicable temperature of these scaling relations was T0 (not Tc) because of the coexistence of stable ferroelectric phase and metastable paraelectric phase in the range between T0 and Tc. As E0 decreased, the lowest applicable temperature shifted to the higher and the temperature range became narrow.

Thermal-induced structural transition and depolarization behavior in (Bi0.5Na0.5)TiO3-BiAlO3 ceramics

The depolarization temperature Td determines the upper temperature limit for the application of piezoelectric materials. However, the origin of depolarization behavior for Bi-based materials still remains controversial and the mechanism is intricate for different (Bi0.5Na0.5)TiO3-based systems. In this work, the structure and depolarization behavior of (1-x)(Bi0.5Na0.5)TiO3-xBiAlO3 (BNT-BA, x = 0, 0.02, 0.04, 0.06, 0.07) ceramics were investigated using a combination of X-ray diffraction and electrical measurements. It was found that as temperature increased, the induced long-range ferroelectric phase irreversibly transformed to the relaxor phase as evidenced by the temperature-dependent ferroelectric and dielectric properties, which corresponded to a gradual structural change from the rhombohedral to the pseudocubic phase. Therefore, the thermal depolarization behavior of BNT-BA ceramics was proposed to be directly related to the rhombohedral–pseudocubic transition. Furthermore, Td (obtained from thermally stimulated depolarization currents curves) was higher than the induced ferroelectric-relaxor phase transition temperature TFR (measured from dielectric curves). The phenomenon was quite different from other reported BNT-based systems, which may suggest the formation of polar nanoregions (PNRs) within macrodomains prior to the detexturation of short-range ferroelectric domains with PNRs or nanodomains.The depolarization temperature Td determines the upper temperature limit for the application of piezoelectric materials. However, the origin of depolarization behavior for Bi-based materials still remains controversial and the mechanism is intricate for different (Bi0.5Na0.5)TiO3-based systems. In this work, the structure and depolarization behavior of (1-x)(Bi0.5Na0.5)TiO3-xBiAlO3 (BNT-BA, x = 0, 0.02, 0.04, 0.06, 0.07) ceramics were investigated using a combination of X-ray diffraction and electrical measurements. It was found that as temperature increased, the induced long-range ferroelectric phase irreversibly transformed to the relaxor phase as evidenced by the temperature-dependent ferroelectric and dielectric properties, which corresponded to a gradual structural change from the rhombohedral to the pseudocubic phase. Therefore, the thermal depolarization behavior of BNT-BA ceramics was proposed to be directly related to the rhombohedral–pseudocubic transition. Furthermore, Td (obtained from thermal...

The depolarization performances of 0.97PbZrO3–0.03Ba(Mg1/3Nb2/3)O3 ceramics under hydrostatic pressure

Several 0.97PbZrO3–0.03Ba(Mg1/3Nb2/3)O3 (0.97PZ–0.03BMN) ceramics were prepared via the columbite precursor method. Their microstructures and pressure-dependent ferroelectric and depolarization performances were then studied. The X-ray diffraction patterns of ground and fresh samples indicate that a main rhombohedral symmetry crystal structure is present in the bulk and that it sits alongside a trace quantity of an orthorhombic antiferroelectric phase that results from the effect of grinding on the surface. The remanent polarization (Pr) of the 0.97PZ–0.03BMN reached 32.4 μC/cm2 at 4.5 kV/mm and ambient pressure. In an in situ pressure-induced current measurement, more than 91% of the retained Pr of the pre-poled sample was released when the pressure was increased from 194 MPa to 238 MPa. That this pressure-driven depolarization should be attributed to the pressure-induced ferroelectric–antiferroelectric phase transition is supported by the emergence of double P–E loops at high hydrostatic pressures. More...

Scaling behavior for (Bi0.5Na0.5)TiO3 based lead-free relaxor ferroelectric ceramics

The dynamic hysteresis and scaling behavior of unpoled 0.96(Bi0.5Na0.5)TiO3-0.04BiAlO3 lead-free relaxor ceramics were investigated through the evolution of the hysteresis loops at a wide frequency (f) and electric-field amplitude (Eo) range. The variation of the hysteresis area ⟨A⟩ and remanent polarization Pr clearly suggested three stages of polarization reversal with increasing external electric fields. It was found that the dynamic hysteresis area in the low-Eo and high-Eo regions followed the power law relationships: 〈 A 〉 ∝ f − 0.14 E o 3.30 (Eo ≤ 5.0 kV/mm) and 〈 A 〉 ∝ f 0.064 E o − 0.6 E o 1.65(Eo ≥ 6.2 kV/mm), respectively. Those power-law functions did not fit in the second stage (5.0 kV/mm < Eo < 6.2 kV/mm), where different numbers of polar nanoregions or nanodomains can be activated and transformed into macrodomains. The polarization mechanisms of above mentioned three stages were ascribed to the domain wall motion, then the formation of microdomains within the disordered nanodomains or polar...

Shock-driven depolarization behavior in BNT-based lead-free ceramics

The pulsed power supply that generates megawatts of electrical power has drawn important attention for many decades. Despite that the large energy output has been obtained in lead-containing materials such as Pb(Zr0.95Ti0.05)O3 (PZT95/5) ceramics, lead-free ferroelectric candidates are highly desired due to the environmental concerns. In this work, we report the depolarization behavior of lead-free ternary 0.99[0.98(Bi0.5Na0.5)(Ti0.995Mn0.005)O3-0.02BiAlO3]-0.01NaNbO3 ferroelectric ceramics under shock wave compression. A current profile with a maximum value of ∼25 A and a FWHM of ∼2.3 μs was obtained. Particularly, the poled BNT-BA-0.01NN ceramics were almost completely depolarized under high strain rate loading, releasing a high charge density J of 38 μC/cm2. The released J was approximately 96% of thermal-induced charge density (∼40 μC/cm2), which was 18% higher than that of PZT95/5 ceramics. The shock-induced depolarization mechanism can be attributed to the ferroelectric-ergodic relaxor phase transition. These results reveal the BNT-based ceramics as promising candidates for pulsed power applications.The pulsed power supply that generates megawatts of electrical power has drawn important attention for many decades. Despite that the large energy output has been obtained in lead-containing materials such as Pb(Zr0.95Ti0.05)O3 (PZT95/5) ceramics, lead-free ferroelectric candidates are highly desired due to the environmental concerns. In this work, we report the depolarization behavior of lead-free ternary 0.99[0.98(Bi0.5Na0.5)(Ti0.995Mn0.005)O3-0.02BiAlO3]-0.01NaNbO3 ferroelectric ceramics under shock wave compression. A current profile with a maximum value of ∼25 A and a FWHM of ∼2.3 μs was obtained. Particularly, the poled BNT-BA-0.01NN ceramics were almost completely depolarized under high strain rate loading, releasing a high charge density J of 38 μC/cm2. The released J was approximately 96% of thermal-induced charge density (∼40 μC/cm2), which was 18% higher than that of PZT95/5 ceramics. The shock-induced depolarization mechanism can be attributed to the ferroelectric-ergodic relaxor phase transit...

Effects of poling state and pores on fracture toughness of Pb(Zr0·95Ti0·05)O3 ferroelectric ceramics

Abstract Abstract The effects of poling state and pores on the fracture toughness of Pb(Zr0·95Ti0·05)O3 (PZT 95/5) ferroelectric ceramics were investigated. X-ray diffraction analysis and piezoelectric constant measurements reveal that the phase structures of PZT 95/5 ceramics change with the poling state, which significantly affects the fracture toughness. The poled PZT 95/5 ceramics demonstrate higher fracture toughness than the unpoled ceramics, and their fracture toughness significantly increases after the pressure depoling. As the porosity of ceramics increases with addition of poreformer during preparation, their fracture toughnesses all decrease accordingly either in poled state or unpoled state. The effect of pore size on the fracture toughness is subtle for the poled ceramics, but for the hydrostatic pressure depoled porous PZT 95/5 ceramics, their fracture toughness increases with the increase in pore size. A new stress model is proposed to explain the pore size effect on the fracture toughness of hydrostatic pressure depoled PZT 95/5 ceramics.