NOVELTY - The flexible device (5) for sealable connection between a metallic substrate and a ceramic substrate separated from one another, comprises a metallic element (30) comprising an end connected to the metallic substrate and another end housed in a groove of the ceramic substrate, and a ground forming a solder joint and connected to the metallic substrate end. The groove is present with an undercut. The metallic element is elastically deformable according to a radial direction of the groove in a gap between the substrates according to the separation direction.    USE - The flexible device is useful in high temperature electrolyzer and solid oxide fuel cell for sealable connection between a metallic substrate and a ceramic substrate separated from one another (all claimed), where the electrolyzer is useful for the production of hydrogen.    ADVANTAGE - The flexible device provides simple, rapid, complete and efficient sealable connection between a metallic substrate and a ceramic substrate of the electrolyzer at high temperature for a long time without any defects thus capable of economically producing hydrogen from the electrolyzer.    DETAILED DESCRIPTION - The flexible device (5) for sealable connection between a metallic substrate and a ceramic substrate separated from one another, comprises a metallic element (30) comprising an end connected to the metallic substrate and another end housed in a groove of the ceramic substrate, and a ground forming a solder joint and connected to the metallic substrate end. The groove is present with an undercut. The metallic element is elastically deformable according to a radial direction of the groove in a gap between the substrates according to the separation direction. The joint is in contact with a part of height of converging lateral wall of the groove, and is close adjustment against the height of the groove above 700 degrees C. The metallic element and the metallic substrate constitute a monoblock part. The end of the metallic element connected to the ceramic element of the groove has a hook shape. The interior of the hook is devoid of the ground forming the joint to carry out the elastic deformation. The metallic element comprises an accordion part housed in the groove of the ceramic substrate. The accordion part is elastically deformable according to the direction of separation between the substrates. The groove has a radial section in the form of dovetail or bead. An INDEPENDENT CLAIM is included for a process for making a sealable connection between a metallic substrate and a ceramic substrate separated from one another.    DESCRIPTION OF DRAWING(S) - The figure shows a transverse cross-sectional view of a flexible connection device.    Electrolyzer cell (1)    Ceramic support (2)    Cathodic interconnector (3)    Anodic interconnector (4)    Connection device (5)    Metallic element. (30)