a medical implant has an element with at least a part thereof which is composed of piezoelectric material . the piezoelectric material is suitable for contact with body tissue and / or body fluids , and has the formula na x k y nbo 3 , with 0 ≦ x ≦ 0 . 8 , 0 . 2 ≦ y ≦ 1 , and x + y = 1 .