Hybrid functional study of proper and improper multiferroics

Stroppa, Alessandro; Picozzi, Silvia

doi:10.1039/b927508h

Cited by 155 publications

(121 citation statements)

References 100 publications

(146 reference statements)

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“…The HSE06 band gaps are 3.82, 3.51, and 3.41 eV for the T ′, S ′, and R phases, respectively. The R phase serves as a benchmark and the calculated E g is in good agreement with the earlier report of 3.40 eV by Stroppa et al31 The S ′ phase exhibits a blueshift by 0.1 eV with respect to the R phase. The band gap of the T ′ phase is further blueshifted by 0.41 eV with respect to R , in excellent agreement with previous experiment, which observed a band gap increase of ≈0.4 eV 32…”

Section: Resultssupporting

confidence: 89%

Understanding Strain‐Induced Phase Transformations in BiFeO₃ Thin Films

et al. 2015

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Experiments demonstrate that under large epitaxial strain a coexisting striped phase emerges in BiFeO3 thin films, which comprises a tetragonal‐like (T′) and an intermediate S′ polymorph. It exhibits a relatively large piezoelectric response when switching between the coexisting phase and a uniform T′ phase. This strain‐induced phase transformation is investigated through a synergistic combination of first‐principles theory and experiments. The results show that the S′ phase is energetically very close to the T′ phase, but is structurally similar to the bulk rhombohedral (R) phase. By fully characterizing the intermediate S′ polymorph, it is demonstrated that the flat energy landscape resulting in the absence of an energy barrier between the T′ and S′ phases fosters the above‐mentioned reversible phase transformation. This ability to readily transform between the S′ and T′ polymorphs, which have very different octahedral rotation patterns and c/a ratios, is crucial to the enhanced piezoelectricity in strained BiFeO3 films. Additionally, a blueshift in the band gap when moving from R to S′ to T′ is observed. These results emphasize the importance of strain engineering for tuning electromechanical responses or, creating unique energy harvesting photonic structures, in oxide thin film architectures.

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Section: Resultssupporting

confidence: 89%

Understanding Strain‐Induced Phase Transformations in BiFeO₃ Thin Films

et al. 2015

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“…First-principles calculation based on density functional theory (DFT) is a powerful tool for study of the structural, electronic, magnetic and ferroelectric properties of materials. 35 Even though in principle the DFT calculation can only deal with the zero-temperature ground state, it remains useful to understand the physics of materials, including those type-II multiferroics. [16][17][18][36][37][38][39] In this work, we pay attention to the full-scale first-principles calculations of the lattice and electronic structures of YCMO not only for checking the above prediction.…”

Section: Lattice Symmetry Considerationmentioning

confidence: 99%

The ferroelectric polarization of Y₂CoMnO₆aligns along the b-axis: the first-principles calculations

Dong

Zhou

et al. 2015

Phys. Chem. Chem. Phys.

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Double-perovskite A2BBO6 oxides with magnetic B and B ions and E*-type antiferromagnetic order (E*-AFM, i.e. the  structure) are believed to exhibit promising multiferroic properties, and Y2CoMnO6 (YCMO) is one candidate in this category. However, the microscopic origins for magnetically induced ferroelectricity in YCMO remain unclear. In this work, we perform detailed symmetry analysis on the exchange striction effect and lattice distortion, plus the first-principles calculations on YCMO. The E*-AFM state as the ground state with other competing states such as ferromagnetic and Aantiferromagnetic orders is confirmed. It is revealed that the ferroelectricity is generated by the exchange striction associated with the E*-AFM order and chemically rdered Mn/Co occupation. Both the lattice symmetry consideration and first-principles calculations predict that the electric polarization aligns along the b-axis. The calculated polarization reaches up to 0.4682 C/cm 2 , mainly from the ionic displacement contribution. The present work presents a comprehensive understanding of the multiferroic mechanisms in YCMO and is of general significance for predicting emergent multiferroicity in other double-perovskite magnetic oxides.

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“…The coexistence of high-temperature magnetism and strong ferroelectricity makes BFO a material with physical properties of practical importance 3,6 . Due to these exceptional characteristics, BFO has become one of the most studied multiferroic materials leading to a wealth of experimental and simulation results covering both structure and dynamics 3,[11][12][13][14][15][16][17] . The keen and continuous interest is equally motivated by the controversies raised by a priori incompatible experimental findings: determination and interpretation of phase diagram, occurence and nature of phase transitions, assignment and characterization of frequency modes from different spectroscopy techniques (Raman, infrared, ...) 3,14,16,18,19 .…”

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High-temperature phonon spectra of multiferroic BiFeO3 from inelastic neutron spectroscopy

Zbiri

Schober

Choudhury

et al. 2012

Applied Physics Letters

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We report inelastic neutron scattering measurements of the phonon spectra in a pure powder sample of the multiferroic material BiFeO3. A high-temperature range was covered to unravel the changes in the phonon dynamics across the Néel (TN ∼ 650 K) and Curie (TC ∼ 1100 K) temperatures. Experimental results are accompanied by ab-initio lattice dynamical simulations of phonon density of states to enable microscopic interpretations of the observed data. The calculations reproduce well the observed vibrational features and provide the partial atomic vibrational components. Our results reveal clearly the signature of three different phase transitions both in the diffraction patterns and phonon spectra. The phonon modes are found to be most affected by the transition at the TC . The spectroscopic evidence for the existence of a different structural modification just below the decomposition limit (TD ∼ 1240 K) is unambiguous indicating strong structural changes that may be related to oxygen vacancies and concomitant Fe 3+ → Fe 2+ reduction and spin transition.PACS numbers: 75.85.+t, 78.70.Nx, 71.15.Mb, 63.20.dk Multiferroism is the combination of two or more of the following properties: ferroelectricity, ferromagnetism and ferroelasticity. In particular, tuning the electric or magnetic properties by applying a magnetic or an electric field, respectively, is at the basis of new applications in microelectronics, spintronics, data storage and computing hardware 1-3 . This explains the strong interest in multiferroic materials from a practical point of view. They unfortunately do not abound in nature and are often difficult to synthesize technologically. Within the most important ABO 3 perovskite family the scarcity of multiferroic properties is mainly due to the d-electrons of the B cation, which on one side are necessary for magnetism but on the other side tend to reduce the tendency for an off-centering ferroelectric distortion 4 . A remarkable exception is bismuth ferrite BiFeO 3 (BFO). This material seems to be unique in exhibiting multiferroic behavior above room temperature. It is simultaneously ferroelectric, antiferromagnetic and ferroelastic, and is subject to crystallographic distortions. The mixture of these multiple order parameters involved in its phase transitions is believed to lead to a very rich phase diagram 3,5 . The physical behavior of BFO is characterized by two largely different transition temperatures; antiferromagnetic with T N ∼ 600 -650 K and ferroelectric with T C ∼ 1050 -1100 K, and a polarization that can reach a very large 3,6 value ∼ 100 µC/m 2 . The large value of the Curie temperature could be at the origin of the observed colossal spontaneous polarization through a strong ferroelectric ordering 7 . The polarization in BFO is mainly caused by the Bi 6s 2 lone pair, so that ferroelectricity is induced primarily via this site (strong cation displacements). Another remarkable aspect of BFO is the occurrence of FeO 6 octahedra tilts accompanying the strong Bi 3+ displacements at room tempera...

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Hybrid functional study of proper and improper multiferroics

Cited by 155 publications

References 100 publications

Understanding Strain‐Induced Phase Transformations in BiFeO₃ Thin Films

Understanding Strain‐Induced Phase Transformations in BiFeO₃ Thin Films

The ferroelectric polarization of Y₂CoMnO₆aligns along the b-axis: the first-principles calculations

High-temperature phonon spectra of multiferroic BiFeO3 from inelastic neutron spectroscopy

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Hybrid functional study of proper and improper multiferroics

Cited by 155 publications

References 100 publications

Understanding Strain‐Induced Phase Transformations in BiFeO3 Thin Films

Understanding Strain‐Induced Phase Transformations in BiFeO3 Thin Films

The ferroelectric polarization of Y2CoMnO6aligns along the b-axis: the first-principles calculations

High-temperature phonon spectra of multiferroic BiFeO3 from inelastic neutron spectroscopy

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Understanding Strain‐Induced Phase Transformations in BiFeO₃ Thin Films

Understanding Strain‐Induced Phase Transformations in BiFeO₃ Thin Films

The ferroelectric polarization of Y₂CoMnO₆aligns along the b-axis: the first-principles calculations