Spontaneous superlattice formation and electrical properties of Sr-excess SrTiO3 thin film deposited on SrTiO3(101) by dynamic aurora pulsed laser deposition

Abstract

Epitaxial Sr-excess SrTiO3 (ST) thin film (Sr/Ti = 1.41) was grown on ST(001) and ST(101) single-crysta substrates using dynamic aurora pulsed laser deposition (PLD) under a 200 mT magnetic field. The film spontaneously formed a superlattice structure comprising two layers having different concentrations o RuddlesdenPopper (RP) planar faults. The superlattice periods of Sr-excess ST thin films deposited on ST(001 and ST(101) substrate were, respectively, 35 and 23 nm. For thin film deposited on ST(001), the in-plane lattic parameter coincided with the substrate, showing coherent growth. For thin film deposited on ST(101), coheren growth occurred along a direction «45° declined against the substrate. The spontaneously formed superlattic was brought about by “up-hill diffusion” of spinodal decomposition. The direction of propagation of th composition wave of spinodal decomposition was regarded as perpendicular to the substrate and «45° decline against the substrate for thin films deposited respectively on ST(001) and ST(101). The superlattice period of th thin film deposited on ST(101) (23 nm) is smaller by a factor of 1=pffiffiffi 2 than that deposited on ST(001). Thi relation is explainable by the difference of the propagation direction of the composition wave. The thin film deposited on ST(001) is distorted tetragonally, whereas that on ST(101) is cubic. The Sr-excess ST thin film wa also deposited on La-doped ST(101) (La-ST(101)) and La-ST(101) substrates to measure electrical properties No change was found in the crystal structure and microstructure, irrespective of La-doping. The thin film deposited on La-ST(001) showed ferroelectricity. However, the film deposited on La-ST(101) shows n ferroelectricity. The difference of electrical properties is brought about by differences of crystal symmetry. Th difference is also explainable from the perspective of thermodynamic phenomenology.