We　investigate　the　potential　profiles　and　elemental　distribution　of　barriers　in　Co/ZrAlOx/Co　magnetic　tunnel　junctions　(MTJs)　using　electron　holography　(EH)　and　scanning　transmission　electron　microscopy.　The　MTJ　barriers　are　introduced　by　oxidizing　a　bilayer　consisting　with　a　uniform　0.45-nm　Al　layer　and　a　wedge-shaped　Zr　layer　(0-2nm).　From　the　scanning　transmission　electron　microscopy,　AlOx　and　ZrOx　layers　are　mixed　together,　indicating　that　compact　AlOx　layer　cannot　be　formed　in　such　a　bilayer　structure　of　barriers.　The　EH　results　reveal　that　there　are　no　sharp　interfaces　between　the　barrier　and　magnetic　electrodes,　which　may　be　responsible　for　a　smaller　tunnelling　magnetoresistance　compared　with　the　MTJs　of　Co/AlOx/Co.