Atomic structure and chemistry of dislocation cores at low-angle tilt grain boundary in SrTiO3 bicrystals

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

“…Because each of the edge dislocations with defined Burgers vector can lie in different planes (so-called slip system) we can observe different combinations between the mentioned crystallographic directions of the dislocations and the plane, e.g., {101}<101>, {110}<001> [70,71], (101){010}, (111){101}, and (100){101} [37]. (i.e., TiO2 or SrO), the configuration corresponds to the generation of a stacking fault, and the dislocation in its character will be partial [65,68]. For rutile crystals, which at room temperature possess a tetragonal structure, the orientation of the edge dislocation can be realized in different directions.…”

“…For the ideal case of the distribution of dislocations along the boundary, one should only observe (after etching of the bicrystal) a kind of overlap of etch pits along a line with a distance of a few nm. Nota bene, such a configuration of the regular distribution on the nanoscale can be directly derived from the HRTEM measurement (see, e.g., [65]). Therefore, for such a position of etch pits one can expect the creation of a continuous canyon with triangular shape (considering the resolution given by an optical microscope) (see Figures 14 and 15).…”

“…However, that this does not mean that we will neglect the other more classical techniques as, for example, etch pits technique or X-ray topography in our presentation. The microscopic analysis, which has become available during recent years, especially by HRTEM (e.g., [4][5][6][7][8][9][10][11][12][13]29,33,46,[60][61][62][63][64][65]) and SPM analysis (e.g., [53,55,[66][67][68]), allows for us to underpin our hypothesis that the dislocations in band-insulating transition metal oxides take the role of semi-conducting or metallic nano-wires (e.g., [3,13,32,40,50,51,55,68]). We place special emphasis on this problem, namely that the properties of the local stoichiometry and specifically the valence of the transition metal cations close to the core of dislocations is responsible for the kind of specific electric properties of the dislocations encountered in these materials and that allows for considering the dislocation lines as a kind of nano-wire extending throughout the crystal.…”

Local crystallographic shear structures in a[201] extended mixed dislocations of SrTiO3 unraveled by atomic-scale imaging using transmission electron microscopy and spectroscopy

“…Using high-angle annular dark-eld scanning transmission electron microcopy (HAADF-STEM) and spectrum imaging techniques, direct experimental evidence for the face-centered cubic (FCC) NaCl-type titanium monoxide (TiO x ) phase at the dislocation cores in low-angle tilt grain boundaries of SrTiO 3 has been presented in previous studies. 15,17 More recently, an interesting report showed a small twist between the two tilt grains leading to the formation of extended mixed [201]/(100) dislocations (here we assign [001] to the tilt axis direction), 18 each of which comprises a complete dislocation (Burger's vector b ¼ a[100]; here, a is the lattice constant for SrTiO 3 ) located between two partial dislocations (b ¼ a/2[101]) along the tilt grain boundary. The cores of the partial dislocations (b ¼ a/2[101]) extend to the middle b ¼ a[100] complete dislocation through the extrinsic stacking faults, which were proposed to be formed by the absence of a {001} Sr-O layer and thereby comprising of two neighboring {001} Ti-O layers.…”

“…15 Besides edge dislocations, in reality faceting and extended dislocations may also occur at the tilt grain boundaries and exert effects on the structural and electrical properties. 16 In order to establish the microstructure-property relationships, it is therefore a prerequisite to study comprehensively atomic structural details of different types of dislocations in real bicrystals.…”