Journal of Materiomics最新文献

A two-step brazing process was successfully employed to join MgF₂ ceramic and TA15 alloy using eutectic Ag28% (in mass fraction) Cu alloy and Bi₂O₃B₂O₃ZnO (BBZ) glass as fillers, by introducing a 100 μm thick GH4169 interlayer. Multiscale characterization revealed that interdiffusion and reaction occurred at the joint interfaces. As a result, a reliable joint system consisting of TA15/TiCu/TiCu₂Al/Ag(s,s) + Cu(s,s)/TiCu₂Al/TiCu Ni + Ag-rich layer/GH4169/nano-oxide layer/glass/Mg₃(BO₃)F₃+MgO + MgF₂ reaction layer/MgF₂ was formed. The GH4169-interlayer exhibited adaptive compatibility though its interaction with AgCu and BBZ glass fillers, effectively accommodating strong interface bonding and thermal mismatch stress between TA15 and MgF₂ substrates. It shows an excellent shear strength (32 MPa, at room temperature) as well as thermal cycling stability without any cracking or spallation observed after the 20 thermal shock cycles between room temperature and 300 °C. It provides valuable insights into designing highly reliable ceramic/metal joints that demonstrate superior stability and adaptability in specific applications.

To date, most of the reported piezoelectric energy harvesters (PEHs) use lead-based Pb(Zr,Ti)O₃ (PZT) piezoceramic family, which is obviously harmful to the environment. In recent years, the PEHs constructed with lead-free piezoceramics have been developed rapidly. However, their force-to-electric (F–E) output performances are still unsatisfactory. To address this issue, here we present a PEH assembled with lead-free potassium sodium niobate (KNN) based co-fired multilayered piezoceramics (MLPCs), which show a high output current and power. First, high-quality KNN-based MLPCs are prepared by tape-casting process. Each MLPC contains 11 piezoceramic layers, and the cross-section SEM image of the MLPC indicates that the ceramic layers are well connected with the Ag/Pd inner electrode layers. The d₃₃ of a single MLPC reaches up to 4675 pC/N. The F–E output performance of KNN-MLPC based PEH is then tested. The inherent advantages of multilayered ceramics enable the PEH to achieve a peak-to-peak output current of up to 1.48 mA and a peak-to-peak output power of 2.19 mW under a harmonic force load of 6 kN at 14 Hz. Finally, the PEH is tested to validate its practical application in real road environments, demonstrating its promising for the use of self-powered monitoring sensors for collecting traffic data.

The poor temperature stability of the BaTiO₃ ceramic has always been the main problem limiting their application. This situation has been improved but sacrifices the intrinsic polarization, which significantly reduces the dielectric constant. In this work, the mechanism of multiple polarization was creatively introduced, and the temperature stability and dielectric properties of BaTiO₃-based ceramics are simultaneously enhanced. In particular, the Ba_0.9925Bi_0.005Ti_0.995Ca_0.005O_2.995 (BBTC0.5) ceramic sample achieved excellent temperature stability (−14.8% to 8.85%) over an ultra-wide temperature range (−47 to 400 °C) and exhibited colossal permittivity (27,125, 25 °C, 1 kHz) and low dielectric loss (0.07, 25 °C, 1 kHz). The dielectric properties, complex impedance spectra combined with XPS results indicate that the defective dipole clusters (${\text{Ti}}^{3+}-V_O^{..}-{\text{Ti}}^{3+}$, ${\text{Bi}}_{\text{Ba}}^{.}$ and ${\text{Ca}}_{\text{Ti}}^{″}-V_O^{..}$) along with surface effects lead to colossal permittivity effect. More importantly, SEM images show the presence of the second phase at grain boundaries, which prevent the carriers within the grains from accumulating at the grain boundaries. As a result, the dielectric loss was reduced and the temperature stability was further extended. This strategy breaks the traditional limitation of single/noncomprehensive enhancement by single-polarization mechanism, and is of great theoretical and practical significance to promote the research and application of high-performance BaTiO₃-based ceramic materials.

Transparent electro-optic (EO) oxide ceramics are known for their rapid EO effects. EO ceramics have several advantages over single-crystals, including variable size and shape, controllable chemical composition, superior mechanical properties, and low cost. Synthesis of high-performance transparent EO ceramics requires high purity of raw materials, high density, homogeneous composition, uniform grain size, and relatively wide bandgap. Powder synthesis and sintering are two of the critical steps involved in the fabrication of highly transparent EO ceramics. Using high-activity precursor powders has been effective in fabricating high-density ceramics that demonstrate excellent EO performance. The sintering process plays a crucial role in achieving this result, and currently, there are several sintering methods available for producing high-density ceramics, including hot-pressing, hot isostatic pressing, and spark plasma sintering. This review summarizes the recent progress in materials and processes used to develop transparent EO ceramics, including those based on lead zirconate titanate, lead magnesium niobate-lead titanate, and lead-free potassium sodium niobate. In addition, several novel applications of transparent EO ceramics, including light shutters, spectral filters, optical memory, as well as image storage and displays are reviewed. In the end, the review concludes with a discussion of future trends and perspectives.