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Sr(Li 1/4 Nb 3/4) x Ti (1- x) O 3 (0.000 ≤ x ≤ 0.04) (STLN) ceramics were synthesized via a solid-state reaction under a flowing nitrogen atmosphere. Co-doping with Li+ and Nb5+ considerably enhanced the dielectric properties of SrTiO 3 ceramics. These dielectric properties increased with the co-doping concentration x up to x = 0.012 and decreased for higher x. The STLN ceramic with x = 0.012 exhibited a colossal permittivity of ε r = 17,300 (1 kHz) and an ultralow dielectric loss of tan δ = 0.017 (1 kHz), with excellent frequency (20–106 Hz) and temperature (room temperature to 450 °C) stabilities. Their dielectric relaxation mechanisms and point-defect structures were also investigated. With an excessive increase in x , the formation of point defects is inhibited, resulting in the deterioration of the dielectric properties of the STLN ceramics. Further studies showed that acceptor doping Li+ and N 2 atmosphere sintering provided a large number of oxygen vacancies. These oxygen vacancies contribute to the formation of some defect dipoles and defect-dipole clusters (Ti Ti ′ − V O • • − Ti Ti ′ , Nb TI • − Ti Ti ′) related to oxygen vacancies. These defect dipoles and defect-dipole clusters restrict non-localized electrons, leading to electron-pinning. Consequently, the sample exhibits colossal permittivity and low dielectric loss. In addition, a high grain boundary resistance also contributes to the reduced dielectric loss. [ABSTRACT FROM AUTHOR]

Niobium oxalate was employed to obtain BiNbO 4 for the first time and the BiNbO 4 nanorods were successfully synthesized through a hydrothermal method at a low temperature. Oxygen vacancies were introduced into the BiNbO 4 nanorods, lowering the BiNbO 4 bandgap. The O-deficient BiNbO 4 exhibited excellent sonocatalytic performance. [ABSTRACT FROM AUTHOR]

In order to relieve high residual stresses between ceramics and metals during brazing processes, an AgCuTi/graphene-reinforced Cu foam composite filler was developed and used to braze the ZrB 2 -SiC ceramic and Inconel 600 alloy. Microstructures and shear strengths of the joints were systematically studied. The joints are composed of TiFe 2 , TiCu, TiC, Cu(s, s), Ag(s, s), and Ti 5 Si 3 phases. It is found the addition of graphene on the Cu foam surface can effectively retard diffusions of metal atoms and avoid the collapse of the foam matrix. After being brazed at 900 °C, the joint can get a maximum shear strength of 157 MPa, much higher than those brazed without graphene addition. The high shear strength was investigated in detail and attributed to the integrity of the Cu foam, formation of the TiC and thickness of the reaction layer at the ceramic side. [ABSTRACT FROM AUTHOR]

Abstract In this paper, brazing behaviors between ZrB 2 SiC and Ti 6Al 4V by Cu foam interlayer were studied. The microstructure, formation mechanism, mechanical property and fracture surface of the joints were systematically studied. The results showed that the phases in the joints were α + β -Ti, TiCu, Ti 2 Cu, Cu(s, s), TiC, TiB 2 and Ti 3 SiC 2. An optimum shear strength reached up to 435 MPa at a brazing temperature of 910 °C and holding time of 20 min. Such a shear strength was 90 MPa higher than the one without the Cu foam. The obtained high shear strength of joint was discussed from microstructure and residual stress. With the increase of brazing time, Cu(s,s) gradually disappeared and the content of Ti 2 Cu intermetallic compound increased, which was harmful for the joint. Furthermore, the residual stress of joint with Cu foam was calculated to be 324 MPa, lower than the one without Cu foam interlayer. [ABSTRACT FROM AUTHOR]

The idea of employing slant grooves to achieve the conversion between the longitudinal vibration and the torsional vibration has been proposed for many years, however, comparative studies on the effectiveness of different forms of diagonal grooves are seldom reported. In this paper, a sandwich longitudinal-torsional (L&T) composite ultrasonic vibrator driven by a longitudinally polarized PZT stack is presented. Four diagonal grooves were equally distributed around the front mass of the vibrator for mode conversion purpose. The grooves can be machined either along thread curves or along straight lines. The influences of the thread grooves on the characteristics of the vibrator were compared with that of the straight grooves both numerically and experimentally. Modal, harmonic and transient analysis were conducted using a finite element model established in a commercial FEM software. Then, prototypes of a transducer and a pair of front mass with thread and straight grooves were manufactured for experimental purpose. The measurement results coincide with the FE simulation prediction. It indicates that although both types of grooves are able to convert the longitudinal vibration into L&T composite vibration, the thread grooves can achieve much larger torsional amplitudes. The present work provides useful information for engineers to make trade-offs between the two sorts of grooves at designing stage. [ABSTRACT FROM AUTHOR]