Flexible polyvinylidene fluoride/(Na 0.5 K 0.5 )NbO 3 (PVDF/NKN) composite harvester was first characterized at high temperature. The origin of high flexibility is the unique structure assembled by alternately stacking four-sheets and three-fabrics (4-3 harvester). The 4-3 harvester was fabricated by uniformly dispersing piezoelectric NKN particles within a PVDF-sheet and a PVDF-fabric layer. Electric power-output of the 4-3 harvester was measured by using a custom-designed apparatus in the temperature range from 25 to 150°C and was compared with that of PVDF/BaTiO 3 (BT) harvester. The PVDF/NKN 4-3 harvesters and PVDF/BT 4-3 harvesters showed significantly different temperature dependences in the temperature range from 25 to 150°C. Electric power-output obtained at 25°C by applying an oscillation at 75 Hz in the thickness direction for the PVDF/ NKN 4-3 harvesters and PVDF/BT 4-3 harvesters were 5.7 and 3.5 nW/cm 2 per an amplitude, respectively. In particular, at temperature above 130°C, the PVDF/NKN 4-3 harvester showed a stable output performance from 3.3 to 3.8 nW/cm 2 , whereas the PVDF/BT 4-3 harvester demonstrated no electric power-output. Thus, the harvester composed of high T C piezoelectric particles such as NKN is suitable as a vibration energy harvester operated under high-temperature environment.

A metal–metal bonding technique is described that uses nanoparticles composed of silver and copper. Colloid solutions of nanoparticles with an Ag content of 0–100 mol% were prepared by simultaneous reduction of Ag+ and Cu2+ using hydrazine with polyvinylpyrrolidone and citric acid as stabilisers. The nanoparticles ranged in size from 34 to 149 nm depending on the Ag content. Copper discs were strongly bonded at 400°C for 5 min under 1.2 MPa pressure in hydrogen gas; the maximum shear strength was as high as 23.9 MPa. The dependence of shear strength on the Ag content was explained by a mismatch between the d-spacings of Cu metal and Ag metal.

The present work describes synthesis of Ag/Cu composite nanoparticles in aqueous solution, and metal-metal bonding in hydrogen gas or nitrogen gas using the nanoparticles. Synthesis of the Ag/Cu composite nanoparticles was performed by the following process. First, a colloid solution of metallic Cu nanoparticles was prepared by reducing copper ions using hydrazine in an aqueous solution containing citric acid and polyvinylpyrrolidone. Then, metallic Ag nanoparticles were fabricated by reducing silver ions with hydrazine in the presence of the metallic Cu nanoparticles. The metallic Ag nanoparticles with a size of ca. 25 nm were immobilized on the metallic Cu nanoparticles with sizes of 60-120 nm. Cu-Cu bonding was performed by pressurizing metallic copper discs sandwiching the nanoparticles as a filler at 1.2 MPa for 5 min under annealing in hydrogen gas or nitrogen gas. The shear strength, which was required to separate the bonded discs, recorded 26.8 and 12.1 MPa for the bonding in hydrogen gas and nitrogen gas, respectively.