Increasing Performances of 1-3 Piezocomposite Ultrasonic Transducer by Alternating Current Poling Method.

Ultrasonic transducers are the basic core component of diagnostic imaging devices, wherein the piezoelectric materials are the active element of transducers. Recent studies showed that the alternating current poling (ACP) method could develop the properties of piezocomposites, which had great potential to improve transducer performance. Herein, transducers (fc = 3 MHz) made of DCP and ACP 1-3 piezocomposites (prepared by PZT-5H ceramics and PMN-PT single crystals) were fabricated. The effect of the ACP method on the bandwidth and insertion loss (sensitivity) was explored. The results indicate that the ACP method can significantly enhance the bandwidth and slightly increase the insertion loss of transducers. Particularly, a superhigh bandwidth of 142.8% was achieved in the transducer of ACP 1-3 PMN-PT single crystal combined with suitable matching and backing layers. This bandwidth is higher than that of all reported transducers with similar center frequency. Moreover, the optimization mechanism of transducer performance by the ACP method was discussed. The obtained results suggested that the ACP is an effective and convenient technology to improve transducer performances, especially for the bandwidth.

Enhancement of Ultrasonic Transducer Bandwidth by Acoustic Impedance Gradient Matching Layer.

High-performance broadband ultrasound transducers provide superior imaging quality in biomedical ultrasound imaging. However, a matching design that perfectly transmits the acoustic energy between the active piezoelectric element and the target medium over the operating spectrum is still lacking. In this work, an anisotropic gradient acoustic impedance composite material as the matching layer of an ultrasonic transducer was designed and fabricated; it is a non-uniform material with the continuous decline of acoustic impedance along the direction of ultrasonic propagation in a sub-wavelength range. This material provides a broadband window for ultrasonic propagation in a wide frequency range and achieves almost perfect sound energy transfer efficiency from the piezoelectric material to the target medium. Nano tungsten particles and epoxy resin were selected as filling and basic materials, respectively. Along the direction of ultrasonic propagation, the proportion of tungsten powder was carefully controlled to decrease gradually, following the natural exponential form in a very narrow thickness range. Using this new material as a matching layer with high-performance single crystals, the -6 dB bandwidth of the PMN-PT ultrasonic transducer could reach over 170%, and the insertion loss was only -20.3 dB. The transducer achieved a temporal signal close to a single wavelength, thus there is the potential to dramatically improve the resolution and imaging quality of the biomedical ultrasound imaging system.

Phase-field simulation on the interaction of oxygen vacancies with charged and neutral domain walls in hexagonal YMnO3.

A three-dimensional model of the interaction between the charged or neutral domain walls and oxygen vacancies in the hexagonal manganite YMnO3was proposed, and simulated using Landau-Ginzburg-Devonshire (LGD) theory, dynamic diffusion equation and Maxwell's equation. The calculation proves that stiffness anisotropic factors can adjust the domain wall state and ultimately affect the distribution of oxygen vacancies. The head-to-head domain wall corresponds to low oxygen vacancy density, and the tail-to-tail domain wall corresponds to high oxygen vacancy density. The electrostatic field generated by the bound charge is the key factor leading to the change of oxygen vacancy distribution. Finally,e-index lawNd=aeb*dP/dzcan fit the relationship between the oxygen vacancy concentration and the polarization gradient alongzdirection. Our theory provides a new way to modulate the distribution of oxygen vacancies through domain wall morphology in hexagonal YMnO3.

Enhancing the Temperature Stability of 0.42PNN-0.21PZ-0.37PT Ceramics through Texture Engineering.

Although the MPB composition 0.42PNN-0.21PZ-0.37PT ceramic has high piezoelectric properties, its temperature stability at room temperature is rather poor due to the low phase-transition temperature. By texture engineering using BaTiO3 (BT) as the template, the temperature stability of this material can be greatly improved. In the temperature range from room temperature up to 140 °C, the high effective piezoelectric strain constant d33* of 0.42PNN-0.21PZ-0.37PT-3BT only changed by 4.9% from 1278 to 1215 pm/V, while the d33* of the nontextured counterpart changed by 46.7% from the room temperature value of 920 pm/V with the maximum deviation to 1350 pm/V at 80 °C. In addition, the textured ceramic has higher piezoelectric properties, lower dielectric loss, and slightly higher coercive field. The room-temperature figure-of-merit d33 × g33 for PNN-PZT-2BT is increased by as much as 42% compared with the nontextured counterpart. Our results demonstrated that texture engineering is an effective way to improve the temperature stability of the MPB composition piezoceramics.

Highly sensitive optical ratiometric thermometry by exciting Eu3+/Tb3+'s unusual absorption lines.

A guideline for designing sensitive thermometry is proposed. It reveals that using two emission bands that possess the opposite change tendencies against temperature makes it easier to achieve a larger relative sensitivity. Based on the guidelines, a highly sensitive strategy for optical thermal detection that depends on the Tb3+-to-Eu3+ emission ratio is designed by exciting Eu3+/Tb3+'s unusual absorption lines. This can be easily driven by a commonly used and cheap 405 nm laser diode. Moreover, its maximum relative sensitivity reaches up to 2.02% K-1 at 610 K, one of the largest sensitivities reported so far.

Green synthesis of benzonitrile using ionic liquid with multiple roles as the recycling agent.

Preparation of benzonitrile from benzaldehyde and hydroxylamine hydrochloride is one of the most advantageous approaches. Nevertheless, it suffers from various constraints such as longer reaction time, corrosion and recovery of hydrochloric acid, the use of metal salt catalysts and their separation. For these reasons, a novel green benzonitrile synthetic route was proposed with ionic liquid as the recycling agent in this study. The results indicated that hydroxylamine 1-sulfobutyl pyridine hydrosulfate salt ((NH2OH)2·[HSO3-b-Py]·HSO4) was an expert alternative to hydroxylamine hydrochloride. Meanwhile, the ionic liquid [HSO3-b-Py]·HSO4 exhibited the multiple roles of co-solvent, catalysis and phase separation, thus the use of metal salt catalyst was eliminated, and no additional catalyst was needed. Hence, the separation process was greatly simplified. When the molar ratio of benzaldehyde to (NH2OH)2·[HSO3-b-Py]·HSO4 was 1 : 1.5, the volume ratio of paraxylene to [HSO3-b-Py]·HSO4 was 2 : 1, the benzaldehyde conversion and benzonitrile yield were both 100% at 120 °C in 2 h. Even better, the ionic liquid could be recovered easily by phase separation, and recycled directly after reaction. Additionally, this novel route is applicable to the green synthesis of a variety of aromatic, heteroaromatic and aliphatic nitriles with excellent yields.

Optimization of electrooptic and pieozoelectric coupling effects in tetragonal relaxor-PT ferroelectric single crystals.

The electrooptic and piezoelectric coupling effects in tetragonal relaxor-based ferroelectric 0.62Pb(Mg1/3Nb2/3)O3-0.38PbTiO3 (PMN-0.38PT) and 0.88Pb(Zn1/3Nb2/3)O3-0.12PbTiO3 (PZN-0.12PT) single-domain crystals have been analyzed by the coordinate transformation. The orientation dependence of the electrooptic and half-wave voltage was calculated based on the full sets of refractive indices, electrooptic and piezoelectric coefficients. The optimum orientation cuts for achieving the best electrooptic coefficient and half-wave voltage were found. The lowset half-wave voltage is only 76 V for the PMN-0.38PT single-domain crystal. Compared to commonly used electrooptic crystal LiNbO3, tetragonal relaxor-PT ferroelectric single-domain crystals are much superior for optical modulation applications because of their much higher linear electrooptic coefficients and substantially lower half-wave voltages when the piezoelectric strain influence is considered.

Electromechanical properties of orthorhombic 0.24Pb(In1/2Nb1/2)O3-0.43Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single-domain crystal.

Single-domain structure with orthorhombic symmetry has been achieved in morphotropic phase boundary composition 0.24Pb(In1/2Nb1/2)O3 -0.43Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 ternary single crystal by applying a large field along the pseudo-cubic direction [011]c. Complete set of elastic, piezoelectric, and dielectric constants has been determined with self-consistency. This crystal shows very large thickness shear piezoelectric coefficient d15=4324 pC/N and extremely high shear electromechanical coupling factor k15=96%. Three-dimensional orientation dependence of the longitudinal piezoelectric constant d33 was calculated and compared with experimental values, which revealed nearly 20% extrinsic contributions in domain engineered [001]c and [111]c poled conditions.

A novel hydroxylamine ionic liquid salt resulting from the stabilization of NH2OH by a SO3H-functionalized ionic liquid.

A SO3H-functionalized ionic liquid was used as an alternative to conventional inorganic acids in hydroxylamine stabilization, leading to the formation of a novel hydroxylamine ionic liquid salt that exhibits improved thermal stability and reactivity in the one-step, solvent-free synthesis of caprolactam in comparison with hydroxylamine hydrochloride and hydroxylamine sulfate.

Landfill leachate production, quality and recirculation treatment in northeast China.

Landfill leachate recirculation treatment process is a promising and economic way in northeast China due to the distinct season variation. In order to study the impact of recirculation on leachate production and its quality, two simulated sanitary landfill reactors, one with leachate recirculation and the other without, were placed outdoor in Harbin. The two-year experimental results indicated that leachate production was reduced by 86% with leachate recirculation and less or no facility for leachate treatment required. Recirculation could improve the leachate quality dramatically with lower COD, SS, NH4(+)-N and higher pH level. Recirculation also could enhance waste degradation and stabilization and improve the efficiency of landfill. This study confirmed that leachate recirculation was a very feasible way for on-site landfill leachate treatment in cold areas.

[Prediction of landfill leachate production in cold area conversion].

Leachate production is evidently discontinuous in the chilly northeast areas because of the distinct 4-seasons conversion and long frozen time. In order to investigate into the leachate production variability and the impact of leachate recirculation on sanitary landfill, two simulated landfill reactors were constructed outdoors, which were filled with the same municipal solid waste. One reactor was provided with leachate recirculation and the other without as a control. On the basis of the obtained leachate production data and evaluation of the available leachate predictive models, the empirical model was recommended and the parameters within the formula were determined through linear regression analysis, which was proved to be reliable and practical. The results provided a scientific basis for the prediction of leachate production, design of leachate collection and treatment system. Besides, this study indicated that leachate recirculation was feasible for leachate treatment in the cold areas.