Magnetic and Electronic Properties of Double Perovskite Ba2SmNbO6 without Octahedral Tilting by First Principle Calculations

The structural, magnetic and electronic properties of the double perovskite Ba2SmNbO6 （for the simple cubic structure where no octahedral tilting exists anymore） are studied using the density functional theory within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction. The total energy, the spin magnetic moment, the band structure and the density of states are calculated. The optimization of the lattice constants is 8.5173 A, which is in good agreement with the experimental value 8.5180 A. The calculations reveal that Ba2SmNbO6 has a stable ferromagnetic ground state and the spin magnetic moment per molecule is 5.00μB/f.u. which comes mostly from the Sin3＋ ion only. By analysis of the band structure, the compound exhibits the direct band gap material and half-metallic ferromagnetic nature with 100% spin-up polarization, which implies potential applications of this new lanthanide compound in magneto-electronic and spintronic devices.

Inhibiting octahedral tilting for stable CsPbI_(2)Br solar cells

The intrinsic phase instability of CsPbI_(2)Br perovskite hinders its development and application in solar cells.Herein,we adopt 1-butyl-3-methylimidazolium hexafluorophosphate(BMIMPF6),a hydrophobic ionic liquid(IL),to improve the phase stability of CsPbI_(2)Br.Density functional theory calculation reveals that the formation energy of CsPbI_(2)Br with BMIMPF6 is reduced,thereby restraining the[PbX_(6)]^(4-) octahedral tilting.The reduced structural distortion and relaxed lattice strain result in improved phase stability of CsPbI_(2)Br.In addition,the interfacial dipole moment increases after introducing BMIMPF6,which facilitates the charge transfer.Consequently,the CsPbI_(2)Br solar cells with BMIMPF6 deliver a power conversion efficiency(PCE)of 16.2%along with excellent stability.The unencapsulated devices with BMIMPF6 maintain 98.9%,88.6%,and 99.5%of the initial PCEs after 1200 h storage in N_(2),1000 h storage in air(30%relative humidity),and 200 thermal cycles(25–100℃),respectively.

Anomalous strain effect in heteroepitaxial SrRuO_(3) films on(111) SrTiO_(3) substrates

We report comprehensive investigations into the structure of high-quality(111)-oriented SrRuO_(3)films on SrTiO_(3)substrates to elucidate the effect of(111)heteroepitaxial strain.We found that SrRuO_(3)film with a thickness of~40 nm is compressively strained in plane on the substrate with full coherency.Nevertheless,the out-of-plane spacing is almost the same as in the bulk,which is at odds with the conventional paradigm.By probing a series of half-order Bragg reflections using synchrotron-based x-ray diffraction combined with analyses of the scanning transmission electron microscopy images,we discovered that the heteroepitaxial strain is accommodated via significant suppression of the degree of c+octahedral tilting and the formation of three equivalent domain structures on the(111)SrTiO_(3)substrate.This anomalous effect sheds light on the understanding of an unconventional paradigm of film-substrate coupling for the(111)heteroepitaxial strain.

Atomic-scale insight into the epitaxial growth mechanism and interfacial coupling of BNT film prepared by hydrothermal synthesis

Revealing the epitaxial growth mechanism and the interfacial coupling effect between oxide films will help to build a“structure-property”bridge for the design of microelectronic devices.Here,the epitaxial growth mechanism and the interfacial coupling in Bi_(0.5)Na_(0.5)TiO_(3)/SrTiO_(3)(BNT/STO)heterointerfaces are investigated by the aberration-corrected scanning transmission electron microscopy,which is synthesized by a hydrothermal method.The results illustrate that 4 mol/L NaOH leads to not only the epitaxial growth of the BNT film but also the mutual diffusion of elements.The uneven distribution of local elements in BNT films is observed and confirmed to impact the cation displacements of B-site and lattice distortion.However,the overall trend of B-site cation displacement at the BNT/STO heterointerfaces is dominated by the interfacial strain.Additionally,the oxygen octahedral tilt exhibits continuous tilt patterns of a^(0)a^(0)a^(0)-a−b^(0)c−-a^(0)a^(0)c−-a^(0)b−c−-a−b−c−from the substrate to BNT film due to the constraint of the substrate and presents a strong correlation with cation displacement.These results are helpful to understand the underlying atomic structures and physical properties of BNT epitaxial thin films.