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Phase diagram of BiFeO3/LaFeO3 superlattices studied by x-ray diffraction experiments and first-principles calculations ; ; Zanolli, Zeila et al in Physical Review. B, Condensed Matter and Materials Physics (2014), 90 Combining structural and functional measurements, we have mapped the phase diagram of BiFeO3/LaFeO3 superlattices grown by off-axis sputtering on (110)o DyScO3 substrates. The phase diagram displays three ... [more ▼] Combining structural and functional measurements, we have mapped the phase diagram of BiFeO3/LaFeO3 superlattices grown by off-axis sputtering on (110)o DyScO3 substrates. The phase diagram displays three distinct regions as a function of BiFeO3 fraction, with a BiFeO3-like ferroelectric phase and a LaFeO3-like paraelectric phase at its extremities, and a complex intermediate region, as supported by first-principles calculations. This intermediate region shows unusual, mixed functional behavior, most likely due to competing phases driven by substitution with a same-size central ion and the specific boundary conditions imposed by the superlattice structure. In the BiFeO3 rich superlattices, scaling of the ferroelectric-to-paraelectric transition temperature with the BiFeO3 thickness could provide an alternate route for studying ferroelectric size effects in BiFeO3. [less ▲] Detailed reference viewed: 28 (3 ULg)Electric control of the magnetization in BiFeO3/LaFeO3 superlattices Zanolli, Zeila ; ; et al in Physical Review B (2013), 88 First-principles techniques are used to investigate the behavior of BiFeO3/LaFeO3 perovskite oxide superlattices epitaxially grown on a (001)-SrTiO3 substrate. The calculations show that 1/1 superlattices ... [more ▼] First-principles techniques are used to investigate the behavior of BiFeO3/LaFeO3 perovskite oxide superlattices epitaxially grown on a (001)-SrTiO3 substrate. The calculations show that 1/1 superlattices exhibit a Pmc21 ground state combining a trilinear coupling of one polar and two oxygen rotational lattice modes, and weak ferromagnetism. The microscopic mechanism allowing one to manipulate the magnetization with an electric field in such systems is presented and its dependence on strain and chemical substitution is discussed. BiFeO3/LaFeO3 artificial superlattices appear to be good candidates to achieve electric switching of magnetization at room temperature. [less ▲] Detailed reference viewed: 32 (2 ULg)First-principles model potentials for lattice-dynamical studies: general methodology and example of application to ferroic perovskite oxides ; Hermet, Patrick ; et al in Journal of Physics : Condensed Matter (2013), 25 We present a scheme to construct model potentials, with parameters computed from first principles, for large-scale lattice-dynamical simulations of materials. We mimic the traditional solid-state approach ... [more ▼] We present a scheme to construct model potentials, with parameters computed from first principles, for large-scale lattice-dynamical simulations of materials. We mimic the traditional solid-state approach to the investigation of vibrational spectra, i.e., we start from a suitably chosen reference configuration of the compound and describe its energy as a function of arbitrary atomic distortions by means of a Taylor series. Such a form of the potential-energy surface is general, trivial to formulate for any material, and physically transparent. Further, such models involve clear-cut approximations, their precision can be improved in a systematic fashion, and their simplicity allows for convenient and practical strategies to compute/fit the potential parameters. We illustrate our scheme with two challenging cases in which the model potential is strongly anharmonic, namely, the ferroic perovskite oxides PbTiO3 and SrTiO3. Studying these compounds allows us to better describe the connection between the so-called effective-Hamiltonian method and ours (which may be seen as an extension of the former), and to show the physical insight and predictive power provided by our approach—e.g., we present new results regarding the factors controlling phase-transition temperatures, novel phase transitions under elastic constraints, an improved treatment of thermal expansion, etc. [less ▲] Detailed reference viewed: 51 (3 ULg)First-principles study of a pressure-induced spin transition in multiferroic Bi2FeCrO6 Goffinet, Marco ; ; Ghosez, Philippe in Physical Review. B, Condensed Matter and Materials Physics (2012), 86 We report on a first-principles study of the structural, electronic, andmagnetic properties of multiferroic double perovskite Bi2FeCrO6, using density functional theory within the local spin-density ... [more ▼] We report on a first-principles study of the structural, electronic, andmagnetic properties of multiferroic double perovskite Bi2FeCrO6, using density functional theory within the local spin-density approximation (LSDA), the LSDA+Uapproximation as well as a hybrid functional scheme.We showthat Bi2FeCrO6 presents two competing ferrimagnetic phases, sharing the same total magnetic moment of 2μB per unit cell but with a different electronic configuration for the Fe3+ species. The phase with high-spin iron is the ground state at ambient conditions, but we predict that low-spin iron gets stabilized under compression.We also investigate the corresponding ferromagnetic phases, and show that the magnetic couplings sharply decrease when moving form high- to low-spin Fe3+. [less ▲] Detailed reference viewed: 64 (3 ULg)A new hybrid exchange-correlation functional for accurate prediction of the electronic and structural properties of ferroelectric oxides Bilc, Daniel ; ; et al in Physical Review. B, Condensed Matter and Materials Physics (2008), 77 Using a linear combination of atomic orbitals approach, we report a systematic comparison of various density functional theory (DFT) and hybrid exchange-correlation functionals for the prediction of the ... [more ▼] Using a linear combination of atomic orbitals approach, we report a systematic comparison of various density functional theory (DFT) and hybrid exchange-correlation functionals for the prediction of the electronic and structural properties of prototypical ferroelectric oxides. It is found that none of the available functionals is able to provide, at the same time, accurate electronic and structural properties of the cubic and tetragonal phases of BaTiO3 and PbTiO3. Some, although not all, usual DFT functionals predict the structure with acceptable accuracy, but always underestimate the electronic band gaps. Conversely, common hybrid functionals yield an improved description of the band gaps, but overestimate the volume and atomic distortions associated with ferroelectricity, giving rise to an unacceptably large c/a ratio for the tetragonal phases of both compounds. This supertetragonality is found to be induced mainly by the exchange energy corresponding to the generalized gradient approximation (GGA) and, to a lesser extent, by the exact exchange term of the hybrid functional. We thus propose an alternative functional that mixes exact exchange with the recently proposed GGA of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] which, for solids, improves over the treatment of exchange of the most usual GGA's. The new functional renders an accurate description of both the structural and electronic properties of typical ferroelectric oxides. [less ▲] Detailed reference viewed: 25 (5 ULg) |
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