Abstract: A center of a multi-layer piezoelectric element is an active region and deforms to a greater degree than ends thereof which is an inactive region during driving operation, and is therefore more susceptible to stress concentration and crack development. To address this problem, a multi-layer piezoelectric element includes a columnar stacked body in which piezoelectric layers and internal electrode layers are alternately laminated, and a pair of external electrodes configured to bond to side faces of the columnar stacked body, wherein a side face of the columnar stacked body is configured so that a surface roughness of a center of the side face in a stacked direction of the columnar stacked body is greater than those of ends of the side face in the stacked direction of the columnar stacked body. This makes it possible to relax the stress exerted on the side face of the columnar stacked body, and thereby enhance the durability of the multi-layer piezoelectric element.

Abstract: A multi-layer piezoelectric element that has high durability with capability to operable continuously under higher voltage and higher pressure over a long period of time, a method for manufacturing the same, an injection apparatus and a fuel injection system are provided. The multi-layer piezoelectric element, comprising: a multi-layer structure comprising a plurality of internal electrode layers and a plurality of piezoelectric material layers, the plurality of piezoelectric material layers being stacked with each one of the plurality of internal electrode layers intervened between each two of the plurality of piezoelectric material layers, wherein a cross-sectional area of a cross section of the multi-layer structure parallel to the plurality of internal electrode layers is smaller in both end portions in a stacked direction than in a middle portion in the stacked direction.

Abstract: A center of a multi-layer piezoelectric element is an active region and deforms to a greater degree than ends thereof which is an inactive region during driving operation, and is therefore more susceptible to stress concentration and crack development. To address this problem, a multi-layer piezoelectric element includes a columnar stacked body in which piezoelectric layers and internal electrode layers are alternately laminated, and a pair of external electrodes configured to bond to side faces of the columnar stacked body, wherein a side face of the columnar stacked body is configured so that a surface roughness of a center of the side face in a stacked direction of the columnar stacked body is greater than those of ends of the side face in the stacked direction of the columnar stacked body. This makes it possible to relax the stress exerted on the side face of the columnar stacked body, and thereby enhance the durability of the multi-layer piezoelectric element.

Abstract: A multi-layer piezoelectric element that has high durability with capability to operable continuously under higher voltage and higher pressure over a long period of time, a method for manufacturing the same, an injection apparatus and a fuel injection system are provided. The multi-layer piezoelectric element, comprising: a multi-layer structure comprising a plurality of internal electrode layers and a plurality of piezoelectric material layers, the plurality of piezoelectric material layers being stacked with each one of the plurality of internal electrode layers intervened between each two of the plurality of piezoelectric material layers, wherein a cross-sectional area of a cross section of the multi-layer structure parallel to the plurality of internal electrode layers is smaller in both end portions in a stacked direction than in a middle portion in the stacked direction.