The microstructures of continuously processed YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) coated conductors processed with three different architectures are presented. YBCO films were deposited directly on ion-beam-assisted deposition (IBAD) yttria-stabilized zirconia (YSZ) or on intervening layers of Y/sub 2/O/sub 3/ or CeO/sub 2/. Different interfacial reactions were observed in each case. The volume changes that occur with the interfacial reactions were calculated based on the identified reaction products. The calculated volume changes correlate with the observed microstructures and appear to be an important factor in determining an optimal buffer layer system. The interfacial reactions do not preclude the attainment of high I/sub c/ and J/sub c/ values in these coated conductors.