Is there any default shortcut to go to material mode in the 3dviewport ?
thanx…
no. because you have to be in the ‘properties’ panel and it is my understanding that panels are context sensitive meaning your mouse have to be over that panel to invoke an operation in that panel and invoking the materials context is only possible in the properties panel.
Someone correct me if my limited bpy.context knowledge is wrong (I know you would anyway 
Not by default but you can simply create your own in the User Preferences / input panel. Look under 3D View / 3D View (Global)
Look at the current ones for wireframe and use MATERIAL as the Value