Bonded body with piezoelectric monocrystalline substrate and supporting substrate

A bonded body comprising a supporting substrate, a piezoelectric monocrystalline substrate and a bonding layer provided between said supporting substrate and said piezoelectric monocrystalline substrate,

• wherein said piezoelectric monocrystalline substrate comprises a material represented by LiAO3 (A represents at least one element selected from the group consisting of niobium and tantalum),
• wherein said bonding layer comprises a material comprising an oxide of at least one element selected from the group consisting of niobium and tantalum,
• wherein said bonded body further comprises an interface layer along an interface between said piezoelectric monocrystalline substrate and said bonding layer, said interface layer having a composition of ExO(1-x) (E represents at least one element selected from the group consisting of niobium and tantalum and 0.29≤x≤0.89), and
• wherein said bonded body further comprises a substrate-side intermediate layer between said interface layer and said piezoelectric monocrystalline substrate, said substrate-side intermediate layer having a composition of GyO(1-y) (G represents at least one element selected from the group consisting of niobium and tantalum and x<y≤0.91).