Threading dislocations in La _0.67 Sr _0.33 MnO ₃ /SrTiO ₃ superlattice

Abstract

Transmission electron microscopy-related experiments were performed on a La 0.67 Sr 0.33 MnO 3 /SrTiO 3 superlattice. The predominant defects in the superlattice are a high density of threading dislocations (TDs) perpendicular or quasi-perpendicular to the substrate surface. The TDs are mostly pure-edge-type with Burgers vectors b = 〈100〉 or 〈110〉. A few TDs of screw character with Burgers vectors ± [001] were also found. Electron energy loss spectra show that non-stoichiometry is accommodated in the near-interface region of the superlattice. The stronger crystal field induced by defect and non-stoichiometry are accounted for by the observed macroscopic properties.

Non-Equilibrium Thermodynamics of Heat Transport in Superlattices, Graded Systems, and Thermal Metamaterials with Defects

“…Here, we provide a simple perspective of several problems, in a qualitative view, in order that the reader may have in mind the physical situations we are examining. We consider three geometrical aspects regarding the structure of the systems, namely superlattices (repetitive structures) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], functionally graded materials (systems with an increase of some particular property along one direction) [17][18][19][20][21][22][23], and thermal metamaterials (artificially manufactured materials with controlled anisotropy and heterogeneity) [25][26][27][28][29][30][31][32][33][34][35][36][37][38]. We also include some material aspects related to the defects (point defects and line defects) and to the applied stress.…”

“…Superlattices refer to systems physically structured in a periodic way, at a nanoscopic, mesoscopic or macroscopic scale [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]41]. For instance, in a number of applications, alternating layers of two different semiconductors, such as Si/Ge, In x Ga 1−x As/In x Al 1−x As, and GaAs/GaAsP, .…”

“…Here, λ e f f A ( l L i ) and λ e f f B ( l L j ) refer to expressions (5) or (6) or any other expression for λ of materials A and B as a function of the Knudsen number.…”

“…The dislocation lines disturb the periodicity of the crystal lattice. The effect of dislocations on thermal conductivity and other transport coefficients (electrical conductivity, Seebeck coefficient) has been well studied from experimental and theoretical points of view [1][2][3][4][5][6][7]. In fact, the dislocation density ρ D (total length of dislocation lines per unit volume, which has units of (length) −2 ) has only a minor effect on the thermal conductivity for dislocation densities smaller than a characteristic value dependent on the material and temperature.…”

“…The electrical, mechanical, and thermodynamical aspects of many kinds of materials are well-known and well-understood. In this review paper, we focus instead on the nonequilibrium thermodynamics and dynamics of anisotropic and inhomogeneous materials, with special interest on three kinds of systems: superlattices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], graded systems [17][18][19][20][21][22][23][24], and thermal metamaterials [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], for which anisotropy and/or inhomogeneity have been shown to be essential to achieve some particular functionality. Such systems, which we describe below, are opening new perspectives on material sciences, either at macroscopic, mesoscopic or nanoscopic scales.…”