Growth and dielectric properties of BaTiO₃/SrTiO₃ artificial lattice with asymmetric stacking sequnce

BaTiO₃ /SrTiO₃ artificial lattices were deposited on (La,Sr)CoO₃ coated MgO(100) single crystal substrate by pulsed laser deposition (PLD). The stacking thickness ratio of consisting BTO and STO layers was varied while one of the consisting layers was maintained at 2 unit cell layer thickness. The stacking periodicity of BTO/STO artificial lattice was, therefore in the range from asymmetric BTO_{2 unit cell}/STO _{32 unit cell} to BTO_{32 unit cell}/STO _{2 unit cell} structure with a total thickness of 100 nm. As the stacking thickness of the BTO layer increased with a fixed stacking thickness of the STO layer (i.e., 2 unit cell thickness), the lattice distortion of the STO layer increased due to mechanical constraint from the thick BTO layer while the lattice distortion of the BTO layer was relatively unchanged. The lattice distortion (c/a) of the STO layer reached at 1.10 for the stacking periodicity of BTO_{32 unit cell}/STO_{2 unit cell}. The multilayer structure with the variable stacking thickness of the STO layer and fixed stacking thickness of the BTO layer exhibited the large variation in the lattice distortion of the BTO layer. The dielectric constant of the BTO/STO artificial lattice decreased with the stacking ratio of the BTO and STO layers. This was attributed to severe lattice distortion of the STO (or BTO) in the multilayer structure of variable stacking thickness of the BTO (or STO) layer. The dielectric constant of the BTO/STO artificial lattice reached a maximum i.e., 1230 at a stacking periodicity of BTO_{2 unit cell}/STO _{2 unit cell}.