Method of forming a joint

A method of joining at least two sintered bodies to form a composite structure, said method comprising:

• providing a first sintered body comprising a first multicomponent metallic oxide having a first crystal structure selected from the group consisting of a perovskitic structure and a fluorite structure;
• providing a second sintered body comprising a second multicomponent metallic oxide having a second crystal structure identical to the first crystal structure;
• applying at an interface between the first sintered body and the second sintered body a joint material comprising at least one metal oxide, wherein (i) the at least one metal oxide comprises at least one shared metal contained in at least one of the first multicomponent metallic oxide and the second multicomponent metallic oxide;
• (ii) the joint material is free of boron, silicon, germanium, tin, lead, arsenic, antimony, phosphorus and tellurium;
• and (iii) the at least one metal oxide has a melting point below a lower of a first sintering temperature of the first multicomponent metallic oxide and a second sintering temperature of the second multicomponent metallic oxide;
• and
• heating the first sintered body, the second sintered body and the joint material to a joining temperature above the melting point of the joint material and below the lower of the first sintering temperature and the second sintering temperature for a period of time sufficient to form a joint between the first sintered body and the second sintered body and thereby provide the composite structure.