Z.G. Zhu

Effect of PMS modification on dielectric and piezoelectric properties in xPMS-(1 − x)PZT ceramics

The structural, dielectric and piezoelectric properties of xPMS–(1 − x)PZT ceramics were investigated as a function of Pb(Mn1/3Sb2/3)O3 (PMS) content by x-ray diffraction, scanning electron microscopy, and dielectric and piezoelectric spectroscopy techniques. All the Pb(Mn1/3Sb2/3)O3–PbZrO3–PbTiO3 (PMS–PZT) samples exhibit a single phase of perovskite structure with tetragonal symmetry. Dielectric studies revealed that the phase transition temperature (Tc) is suppressed with increasing PMS content. For PMS–PZT samples with 0.08 ≤ x ≤ 0.15, the maximum dielectric constant decreases as the measurement frequencies increase and the permittivity maximum temperature (Tm) is shifted towards higher temperatures as well, which indicates that dielectric relaxor behaviour was observed, while for x = 0.02 and 0.05, there is no shift in Tm, which implies normal ferroelectric behaviour. The samples with a composition of x = 0.05 exhibit excellent dielectric and piezoelectric properties (er = 1540, d33 = 360 pC N−1, Kp = 0.58, tan δ = 0.45%, Qm = 1210) and, therefore, should be ideal candidates for high-power applications, such as in piezoelectric transformers.

Internal friction study of Pb(Zr,Ti)O3 ceramics with various Zr/Ti ratios and dopants

The Pb(Zr,Ti)O3 (PZT) ceramics with Zr/Ti ratios of 30/70, 52/48 and 70/30 and the PZT(52/48) ceramics doped with La, Ta and Co at various percent were prepared by a standard solid-state reaction method, respectively. Internal friction and modulus were measured as a function of temperature at low frequencies by using a inverted torsion pendulum. Two internal friction peaks (P1 and P2), related to oxygen vacancies and domain walls, respectively, were observed in all the undoped PZT ceramics with different Zr/Ti ratios. In addition, a minimum in modulus associated with a phase transition internal friction peak appearing at Curie temperature was observed in all samples. The effects of the Zr/Ti ratios and some dopants (such as La, Ta and Co) on the internal frictions were investigated. The internal friction results indicate the changes of the concentration of oxygen vacancies and the domain structure with the variations of Zr/Ti ratios and dopants, which will be helpful in the utilities of the PZT ceramics.

Binary rare earth element-Ni/Co metallic glasses with distinct β-relaxation behaviors

We report the formation of a series of rare earth element (RE)-Ni/Co binary metallic glasses (MGs) with unusual distinct β-relaxation peak compared with that of most of the reported MGs which usually exhibit as an excess wing or a shoulder. The β-relaxation behavior of RE-Ni/Co MGs is sensitive to the composition and the atomic radii of the RE and can be tuned through changing the fraction of RE-Ni (or Co) atomic pairs. The novel RE-Ni/Co MGs with distinct β-relaxation can serve as model system to investigate the nature of the β-relaxation as well as its relations with other physical and mechanical properties of MGs.

Dynamics of PEO–PPO–PEO triblock copolymer in aqueous solutions investigated by internal friction

The dynamics of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) in aqueous solutions in the range of the polymer concentration Φ = 10.0-45.0 wt% has been investigated by the tube inversion method and the internal friction technique. At Φ ≤ 31.0 wt%, two internal friction peaks are observed with the characteristics of the first-order phase transition, corresponding to the opaque liquid-to-liquid transition and the phase separation. The opaque liquid-to-liquid transition is due to the sphere-to-rod transition in shape of the micelles, and the phase separation is caused by the destruction of core-shell structure. At Φ ≥ 32.0 wt%, besides the internal friction peak associated with phase separation, two other peaks are observed, which correspond to the solution-to-gel (liquid-to-crystal) transition and gel-to-solution (crystal-to-liquid) transition, respectively. The former is due to the micelle crystallization, whereas the latter is the result of spherical micelles fusing into wormlike or rodlike micelles at elevated temperatures.

Mechanism of internal friction in Cu–Al–Mn shape memory alloy

Electrical resistivity and low frequency internal friction (IF) measurements have been performed during constant heating rate. At low frequency, a high IF peak is observed which is in good accordance with the hump appearing in electrical resistivity. It is shown that this IF is not proportional to (where is the temperature rate and f is the vibration frequency). This behavior is systematically investigated.

Effects of molecular weight on the liquid-liquid transition in polystyrene melts studied by low-frequency anelastic spectroscopy

A substantial internal friction peak associated with the liquid-liquid transition (Tll) has been observed in polystyrene (PS) melts with different molecular weights Mw. The peak is of the relaxation type and suggested to be caused by the cooperative rearrangement of PS chains. The relaxation time follows the Vogel–Fulcher–Tamman equation. With increasing Mw, the PS melt exhibits a higher energy barrier, a smaller concentration of mobile species, and a stronger coupling between mobile species at Tll. In addition, to quantify the strength of the temperature dependence of the relaxation time, a parameter mll is defined for PS melt according to Angell’s fragility concept. The value of mll decreases with increasing Mw, indicating a slower cooperative rearrangement of PS chains toward Tll. Moreover, at Mw⩽52.5kg∕mol, mll rapidly drops with Mw, while it more slowly decreases at Mw>52.5kg∕mol. The fact suggests more topological constraints due to the intrachain interactions in very long chains.

DIELECTRIC RELAXOR BEHAVIOR OF Pb(Mn1/3Sb2/3)O3-Pb(Zr0.52Ti0.48)O3 CERAMICS

ABSTRACT In this paper, xPb(Mn1/3Sb2/3)O3-(1−x)Pb(Zr0.52Ti0.48)O3 (PMS-PZT) ceramics were fabricated by using conventional ceramics technique. Temperature and frequency dependence of the dielectric properties of ceramics were investigated. For PMS-PZT ceramics with 0.08 ≤ x ≤ 0.15, the maximum dielectric constant decrease as the measurement frequency increases and its permittivity maximum temperature (T m) is shifted towards higher temperatures as well, these behavior show ‘relaxor-like’ ferroelectric behavior. While for x = 0.05, there is no shift in transition temperature which shows normal ferroelectric behavior. The mechanism of dielectric relaxor behavior for high PMS content is discussed in the paper.

Laser guided ionic wind

We report on a method to experimentally generate ionic wind by coupling an external large electric field with an intense femtosecond laser induced air plasma channel. The measured ionic wind velocity could be as strong as >4 m/s. It could be optimized by increasing the strength of the applied electric field and the volume of the laser induced plasma channel. The experimental observation was qualitatively confirmed by a numerical simulation of spatial distribution of the electric field. The ionic wind can be generated outside a high-voltage geometry, even at remote distances.

Harmonic generation at air-soil interface by femtosecond laser filament

We observe the third-harmonic generation and second-harmonic generation together with element fluorescence from the interaction of a femtosecond laser filament with a rough surface sample (sandy soil) in non-phase-matched directions. The harmonics prove to originate from the phase-matched surface harmonics and air filament, then scatter in non-phase-matched directions due to the rough surface. These harmonics occurr when the sample is in the region before and after the laser filament, where the laser intensity is not high enough to excite the element fluorescence. The observed harmonics are related to the element spectroscopy, which will benefit the understanding of the interaction of the laser filament with a solid and be helpful for the application on filament induced breakdown spectroscopy.

Ab initio molecular dynamics simulations on structure change of liquid Te from normal- to supercooled-state

Using ab initio molecular dynamics simulations and inherent structure formalism, the local atomic structures and electronic properties of liquid Te from the normal- to supercooled-state were studied. The calculated structure factors agree acceptably with available experimental data. There is a noticeable maximum at around 723 K in the curve of first-peak-height of S(Q) versus temperature. With increasing temperature, in the low-temperature region from 573 to 673 K, the average coordination number increases gradually in contrast to the behavior of a classical isotropic fluid; but in the high-temperature region from 843 to 1073 K, it remains nearly constant. Our calculated angular limited bond–bond correlation functions first show that there are two types of Peierls distorted local atomic structures in liquid Te: the lengths of short and long bonds in the first type are similar to those in crystalline Te, while the lengths of short and long bonds in the second one are very different from those in crystalline Te. With decreasing temperature, the lengths of the two short intrachain bonds are unchanged, but those of the two long interchain bonds become longer, indicating that the interchain correlation reduces with decreasing temperature. Our results suggest that the change of the Peierls-type distorted local atomic structures with temperature may be responsible for the striking anomalies of many thermophysical properties of liquid Te. The calculated DOS and LDOS shows that there is an obvious dip in DOS at EF, but the dip at 1073 K is shallower than that at 573 K. The variation of the dip in DOS mainly results from the change of Te p orbital.