Yudong Hou

Effect of Li2CO3 addition on the dielectric and piezoelectric responses in the low-temperature sintered 0.5PZN–0.5PZT systems

Low-temperature sintering of 0.5Pb(Zn1∕3Nb2∕3)O3–0.5Pb(Zr0.47Ti0.53)O3 ceramics (0.5PZN–0.5PZT) was investigated using Li2CO3 as sintering aids. The addition of Li2CO3 significantly improved the sinterability of 0.5PZN–0.5PZT ceramics, resulting in a reduction of sintering temperature from 1100to950°C. Moreover, the effect of Li2CO3 addition on the dielectric and piezoelectric responses in 0.5PZN–0.5PZT systems was systematically studied in this work. The analysis of x-ray diffraction patterns and scanning electron microscopy indicated that the solubility limit of Li ions in perovskite structures was near 0.5wt% in Li2CO3 form. Below the solubility limit, Li+ ions entered the six-fold coordinated B sites of oxygenic octahedral center and enhanced the compositional fluctuation in nanoscale, resulting in the increase of the degree of diffuseness γ. While at high doping level above the solubility limit, γ decreased subsequently, which was attributed to the formation of pyrochlore phase. Raman analysis on the...

Improving Dielectric Properties of PVDF Composites by Employing Surface Modified Strong Polarized BaTiO3 Particles Derived by Molten Salt Method

BaTiO3/polyvinylidene fluoride (BT/PVDF) is the extensive reported composite material for application in modern electric devices. However, there still exists some obstacles prohibiting the further improvement of dielectric performance, such as poor interfacial compatibility and low dielectric constant. Therefore, in depth study of the size dependent polarization and surface modification of BT particle is of technological importance in developing high performance BT/PVDF composites. Here, a facile molten-salt synthetic method has been applied to prepare different grain sized BT particles through tailoring the calcination temperature. The size dependent spontaneous polarizationof BT particle was thoroughly investigated by theoretical calculation based on powder X-ray diffraction Rietveld refinement data. The results revealed that 600 nm sized BT particles possess the strong polarization, ascribing to the ferroelectric size effect. Furthermore, the surface of optimal BT particles has been modified by water-soluble polyvinylprrolidone (PVP) agent, and the coated particles exhibited fine core-shell structure and homogeneous dispersion in the PVDF matrix. The dielectric constant of the resulted composites increased significantly, especially, the prepared composite with 40 vol % BT loading exhibited the largest dielectric constant (65, 25 °C, 1 kHz) compared with the literature values of BT/PVDF at the same concentration of filler. Moreover, the energy storage density of the composites with tailored structure was largely enhanced at the low electric field, showing promising application as dielectric material in energy storage device. Our work suggested that introduction of strong polarized ferroelectric particles with optimal size and construction of core-shell structured coated fillers by PVP in the PVDF matrix are efficacious in improving dielectric performance of composites. The demonstrated approach can also be applied to the design and preparation of other polymers-based nanocomposites filled with ferroelectric particles to achieve desirable dielectric properties.

Effect of lattice occupation behavior of Li+ cations on microstructure and electrical properties of (Bi1/2Na1/2)TiO3-based lead-free piezoceramics

The multisite occupation of Li+ cations in perovskite structure of (Bi1/2Na1/2)TiO3-based solid solution is investigated, which is rarely reported in previous studies. The multisite occupation in relation to the Li2CO3 doping level has been demonstrated with the aid of the microstructure and temperature-dependent conductivity analysis: As the addition of Li2CO3 is below 0.75 mol. %, the introduced Li+ cations precede to enter the A sites of the perovskite lattice to compensate for the A-site deficiency stemming from the high-temperature sintering process. Once the addition exceeds 0.75 mol. %, the excess Li+ cations will occupy B sites to substitute for Ti4+ and give rise to the generation of oxygen vacancies. The proposed multisite occupation behavior of Li+ cations and its derivative effects, involving the clamping effect or grain size effect, have made the piezo-/ferroelectric performances of the 0.85BNT–0.10BKT–0.05BT ceramics optimized at the Li2CO3 addition of 1.0 mol.%:d33 = 163 pC/N, Pr = 40.9 μC/cm2.

Relaxor behavior of (K0.5Bi0.5)TiO3 ceramics derived from molten salt synthesized single-crystalline nanowires

Single-crystalline K0.5Bi0.5TiO3 nanowires have been fabricated by a large scale and facile molten salt synthetic method in a KCl medium. Pristine nanowires have diameters of about 40nm and lengths exceeding 4μm, and they possess tetragonal perovskite structure. The K0.5Bi0.5TiO3 ceramics with a relative density above 98% can be fabricated from high quality nanowires. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed, which can be well fitted by a modified Curie-Weiss law and a Vogel-Fulcher relationship. The suggested relaxor behavior in K0.5Bi0.5TiO3 composition is possibly due to the A-site compositional fluctuations at the nanolevel.

Facile synthesis and high d33 of single-crystalline KNbO3 nanocubes

Single-crystalline KNbO(3) nanocubes with orthorhombic phase were prepared in a large scale by a simple one-step molten salt route without using any surfactant as template; the nanostructures exhibited high piezoelectric properties such as d(33)=105 pC/N and k(p)=0.34 as piezoelectric materials.

Relaxor behavior of (Ba,Bi)(Ti,Al)O3 ferroelectric ceramic

Perovskite type (Ba0.9Bi0.1)(Ti0.9Al0.1)O3 (BBTA) ceramics have been prepared through solid state reaction route. The room temperature x-ray diffraction study suggests that BBTA ceramics have single phase tetragonal symmetry with space group P4mm. In contrast to the sharp dielectric transition of pure BaTiO3, a broad dielectric anomaly coupled with the shift in dielectric maxima toward a higher temperature with increasing frequency has been observed in BBTA. The quantitative characterization based on empirical parameters (ΔTm, γ, ΔTrelax, and ΔTdiffuse(1 kHz)) confirms its relaxor nature. The dielectric relaxation which follows the Vogel–Fulcher relationship with Eα=0.011 eV, Tf=356 K, and f0=1.38×1010 Hz, further supports spin-glass-like characteristics. In this system, the relaxor behavior can be attributed to the dynamic response of the polar clusters induced by the combined substitutions of Bi3+ and Al3+ on the Ba2+ and Ti4+ site. Moreover, the curie temperature of BBTA shows the decreasing trend comp...

Effect of sintering temperature on the phase transition and dielectrical response in the relaxor-ferroelectric-system 0.5PZN–0.5PZT

Relaxor ferroelectrics of 0.5Pb(Zn1∕3Nb2∕3)O3–0.5Pb(Zr0.47Ti0.53)O3 (0.5PZN–0.5PZT) near the morphotropic phase boundary (MPB) were prepared using the conventional oxide mixing method. The influence of sintering temperature on the phase transition and dielectrical response in the relaxor-ferroelectric-system 0.5PZN–0.5PZT has been investigated. X-ray diffraction analysis indicated that the phase of the material changed from an initially rhombohedral structure to a MPB structure and then a tetragonal structure when the sintering temperature is increased from 900to1250°C. The corresponding grain size is enlarged from 1.1μm for predominantly rhombohedral to 2.5μm for more than 60% tetragonal, which obeys the common grain-growth law. The dielectric studies revealed that the indicator of the degree of diffuseness γ decreased with the increase of the sintering temperature from 900to1150°C, indicating that the dielectric relaxor behavior was weakened, while at high sintering temperature above 1250°C, γ increased...

Effect of sintering temperature on dielectric relaxation and Raman scattering of 0.65Pb(Mg1/3Nb2/3)O3−0.35PbTiO3 system

Relaxor ferroelectrics of 0.65Pb(Mg1/3Nb2/3)O3−0.35PbTiO3 (PMN–35PT) were prepared using the columbite precursor proceeding. The influences of sintering temperature on the phase transition, dielectrical response, and Raman scattering in the relaxor-ferroelectric-system PMN–35PT have been investigated in detail. X-ray diffraction analysis indicated that the phase structure of the materials changed from rhombohedral to tetragonal when the sintering temperature increased from 1000 to 1250 °C. The stress relaxation induced by the enlarged grain size was responsible for the phase transition phenomena. The dielectric studies revealed that the indicator of the degree of diffuseness γ decreased with the increase in the sintering temperatures from 1000 to 1150 °C, indicating that the dielectric relaxation behavior was weakened; while at higher sintering temperature above 1200 °C, γ increased subsequently due to the formation of Pb vacancy. The Raman analysis provided another evidence for the phase transition from ...

Dependence of depolarization temperature on cation vacancies and lattice distortion for lead-free 74(Bi1/2Na1/2)TiO3–20.8(Bi1/2K1/2)TiO3–5.2BaTiO3 ferroelectric ceramics

In this paper, the off-morphotropic-phase-boundary 74(Bi1/2Na1/2)TiO3–20.8(Bi1/2K1/2)TiO3–5.2BaTiO3 ceramics were fabricated at different sintering temperatures. It was found out that as the sintering temperature increases, the volatilization of the A-site elements is aggravated, thus generating the oxygen vacancies; meanwhile, the tetragonality of the perovskite lattice reduces gradually. Besides, the temperature-dependent dielectric responses revealed that as the sintering temperature increases, the depolarization temperature Td decreases while the Curie–Weiss point TC increases. It is suggested that the lattice distortion, other than the oxygen vacancies, is the crucial factor in influencing the depolarization temperature.

Effects of Fe 2 O 3 addition on microstructure and piezoelectric properties of 0.2PZN–0.8PZT ceramics

In this work, the effect of Fe 2 O 3 addition on the microstructure and piezoelectric properties of Pb(Zn 1/3 Nb 2/3 ) 0.2 Ti 0.4 Zr 0.4 O 3 (0.2PZN–0.8PZT) ceramics were investigated. The studies indicated that the solution limit of Fe 2 O 3 in the lattice of perovskite structure was about 0.1 wt%. Phase analysis shows that small addition of doping Fe 2 O 3 results in the phase evolution from rhombohedral to tetragonal, sharp decrease of the Curie temperature, and remarkable increase of the grain size. Meanwhile, Fe 2 O 3 addition within the solution limit led to the increase of the e r , k p , and d 33 . It is believed that the variation in the dielectric and piezoelectric properties are closely related to the microstructure change, phase evolution, and tetragonal distortion as Fe 2 O 3 added.