Structure of twin boundaries in La2 − xBaxCuO4

Shape of a twin as related to the inelastic forces acting on twinning dislocations inYBa2Cu3OBoyko1, Chan2, Chopra3 2001Phys. Rev. B240320View full textAdd to dashboardCite

“…Different calculations carried out by different authors [28][29][30][31] led to the similar results. The differences among results were mostly in the values of N and the choice of elastic constant.…”

Thermally activated dynamics of the tilts of the CuO6octahedra, hopping of interstitial O, and possible instability towards the LTT phase in La2CuOCordero1, Grandini2, Cannelli3 et al. 1998Phys. Rev. B365240View full textAdd to dashboardCite

“…These smooth domain walls can also be explained by constructing a model Landau free energy which reproduces the phase diagram of La 2Ϫx Ba x CuO 4 and minimizing it along the twin boundary, with the tilt angles as order parameters. 12 These authors found that their model free energy has a local minimum for the LTT distortion also in undoped La 2 CuO 4 . 12 Then, it is possible that also in La 2 CuO 4 the domain walls are wide and unstable against the formation of the LTT or HTT phase, and peak T can be due to the thermally activated switching of entire octahedra between the two nearly energetically equivalent configurations.…”

“…11,10 Both types of tilts have also been observed in the twin boundary regions of LTO La 2Ϫx Ba x CuO 4 ͑Ref. 3͒, and it is under debate whether the formation of the LTT phase occurs through a widening of the domain walls 12 or is mainly nucleated within the LTO domains. 13 Signs of the tendency of the LTO lattice to form LTT domains also in La 2Ϫx Sr x CuO 4 and even in La 2 CuO 4 are the large anisotropic vibration amplitudes of the O atoms deduced by neutron diffraction, 6 the low energies of the phonon modes involved in the rotations of the octahedra 14 and a softening of the in-plane shear below 50 K in La 1.86 Sr 0.14 CuO 4 .…”

“…Since there are no signs of a precise temperature at which the acoustic dispersion starts, we interpret process L as relaxation among offcenter positions created by the lattice instability toward the LTT-like tilts. Whether this can occur only in particularly disordered or unstable regions like the twin walls or also within the LTO domains, is a question connected with the issue whether the LTT phase propagates from the twin walls 12 or also nucleates in the LTO domains. 13 The extremely broad shape of the Q Ϫ1 (T) curves below 40 K and the fact that their shift to higher temperature at higher frequency is less marked than for the other processes, is not unusual at such low temperature, where the relaxation rate Ϫ1 is generally governed by quantum effects.…”

Twin boundary energy and characterization of charge redistribution near the twin boundaries of cupperate superconductors

“…Moreover it is assumed that each grain is elastically bound to the neighboring grains and also entropy effects expectedly would introduce fluctuations around the above predicted value for the TWs (in the case of thin layer samples the G parameter is replaced by the layer's thickness) [22]. The validity of the above equation has also been confirmed in poly-crystalline samples by various authors [23][24][25][26].…”