Strain-induced single-domain growth of epitaxial SrRuO3 layers on SrTiO3: A high-temperature x-ray diffraction study

Abstract

Temperature dependent structural phase transitions of SrRuO 3 thin films epitaxially grown on SrTiO 3 (001) single crystal substrates have been studied using high-resolution x-ray diffraction. In contrast to bulk SrRuO 3 , coherently strained epitaxial layers do not display cubic symmetry up to ~730 o C and remain tetragonal. Such behavior is believed to be induced by compressive strain between the SrRuO 3 layer and SrTiO 3 substrate due to lattice mismatch. The perovskite SrRuO 3 (SRO) thin films have attracted considerable interest due to their low room temperature resistivity and small lattice mismatch with a range of functional oxide materials. [1][2][3] In order for SrRuO 3 to grow coherently on a single crystal substrate, matching of layer in-plane lattice parameter to that of a substrate is required. The mismatch between in-plane lattice parameters of a film and the substrate introduces strain which affects the structural and electrical properties of the SrRuO 3 layer.For bulk SrRuO 3 , x-ray and neutron diffraction studies show that at room temperature the SrRuO 3 structure possesses an orthorhombic Pbnm symmetry with a = 5.5670 Å, b = 5.5304 Å, and c = 7.8446 Å, similar to other ABO 3 perovskite compounds, and is isostructural with GdFeO 3 . 4 The orthorhombic phase can be obtained by rotation of BO 3 (RuO 3 ) octahedra counterclockwise about the [010] cubic and [001] cubic directions and clockwise rotation about the [100] cubic direction of an ABO 3 cubic perovskite. At around 550 o C, the orthorhombic structure transforms into a tetragonal one with the space group I4/mcm. 5 In the tetragonal unit cell, RuO 3 octahedra are rotated only about the [001] cubic ABO 3 direction. At even higher temperatures of about 680 o C, tetragonal SrRuO 3 transforms into a cubic structure with a standard perovskite space group Pm3m where no rotations of RuO 3 octahedra are observed. 5 As reported by Maria et al.,6 thin SRO films grown on SrTiO 3 (001) (STO) substrates undergo an orthorhombic to tetragonal (O-T) structural phase transition at a somewhat lower temperature of ~350 o C. They also measured a tetragonal to cubic (T-C) phase transition temperature of ~600 o C, but this was obtained from a bulk SrRuO 3 sample. The suggested transitions imply that SrRuO 3 exhibits cubic symmetry during film synthesis, which is typically in the range of 600-700 o C. 6 Since the T-C transition was observed on a powder SrRuO 3 sample, which does not represent conditions of commensurate strained layer growth, it is still unclear what crystal symmetry strained epitaxial SrRuO 3 layer possesses during growth under constrained geometries imposed by the substrate.

Magnetotransport and Hall effect studies of SrRuO3/SrTiO3superlattices

“…This yields a pseudocubic lattice constant of a pc = 3.93 Å, slightly bigger than the STO lattice constant a S T O = 3.905 Å. When grown on vicinal (001) STO with the miscut terrace edges along one of the STO crystallographic directions, the SRO [001] o axis aligns along the terrace edges [6], the compressive strain leads to a monoclinic distortion with the [110] o axis slightly off the film normal with an angle of 89.2 • between a and b axis, for thin films an additional (triclinic) distortion of 0.012 • between [001] o axis and the ab-plane was reported [7]. Recently, a comprehensive review on SRO thin films was published by Koster et al [8].…”

Tilt transitions in compressively strained AgTa0.5Nb0.5O3thin fi

“…11 In other reports, strain was used to modify the room temperature phase as well as phase transition temperatures in tilted systems such as SrRuO 3 and CaRuO 3 thin films. [12][13][14] The materials choice in these published works deals with systems that exhibit relatively simple tilt structures. The research presented in this manuscript examines a more complicated perovskite material, AgTa x Nb 1-x O 3 , which undergoes a complex behavior of octahedral rotations that is in turn coupled to local cation displacements.…”

Synthesis science of SrRuO3 and CaRuO3 epitaxial films with high residual resistivity ratios

“…This agrees with the observation of other groups that the surface step edges on the SrTiO 3 substrate promote the nucleation of a single domain throughout the film below the tetragonal-to-orthorhombic transition of the SrRuO 3 film. [105][106][107] FIG. 2.…”