13 November 2013


Massimiliano Stengel

    Nature Communications 4, Article number: 2693


A mechanical deformation of a continuum can be expressed as a generalized coordinate transformation of space. Consequently, the equations of electrostatics in deformable media must satisfy covariance requirements with respect to such transformations, a problem that has long been addressed in the context of general relativity. Here we show how these ideas can be incorporated into the framework of density-functional perturbation theory, providing access to the microscopic charge density and electrostatic potential response to an arbitrary deformation field. We demonstrate the power of our approach by deriving, in full generality, the surface contributions to the flexoelectric response of a finite object, a topic that has recently been a matter of controversy. The breakdown of translational periodicity produces consequences that might seem highly paradoxical at first sight: for example, the macroscopic bulk polarization does not always correspond to the physical surface charge.

      FIGURE: The three main types of strain gradients producing a dipole moment normal to the surfaces are shown: longitudinal (a), transverse (b) and shear (c). The supercell boundaries are shown as dashed lines, the slabs are schematically represented as arrays of black circles. 


    Hits: 7328
    Oxides for new-generation electronics

    Microscopic response to inhomogeneous deformations in curvilinear coordinates

    Also at ICMAB

    • Stabilization of the Ferroelectric Phase in Epitaxial Hf1–xZrxO2 Enabling Coexistence of Ferroelectric and Enhanced Piezoelectric Properties

      18 June 2021 228 hit(s) Oxides
      Systematic studies on polycrystalline Hf1–xZrxO2 films with varying Zr contents show that HfO2 films are paraelectric (monoclinic). If the Zr content is increased, films become ferroelectric (orthorhombic) and then antiferroelectric (tetragonal). HfO2 shows very good insulating properties and it is used in metal-oxide-semiconductor field-effect devices, while ZrO2 shows good piezoelectric properties, but it is antiferroelectric. In between, Hf0.5Zr0.5O2 shows good ferroelectric properties at the expense of poorer insulating and piezoelectric properties than HfO2 and ZrO2, respectively.
    • Epitaxial Ferroelectric HfO2 Films: Growth, Properties, and Devices

      25 May 2021 243 hit(s) Oxides
      About ten years after ferroelectricity was first reported in doped HfO2 polycrystalline films, there is tremendous interest in this material and ferroelectric oxides are once again in the spotlight of the memories industry. Great efforts are being made to understand and control ferroelectric properties. Epitaxial films, which have fewer defects and a more controlled microstructure than polycrystalline films, can be very useful for this purpose. Epitaxial films of ferroelectric HfO2 have been much less investigated, but after the first report in 2015 significant progress has been achieved.
    • Structure and phase transitions in A-site ordered RBaMn2O6(R=Pr,Nd) -perovskites with a polar ground state

      14 May 2021 258 hit(s) Oxides
      We report here a structural study of RBaMn2O6 (R=La, Pr, and Nd) compounds by means of synchrotron radiation x-ray powder diffraction and Raman spectroscopy. The three compounds are A-site ordered perovskites adopting the prototypical tetragonal structure at high temperature. A ferromagnetic transition is observed in the LaBaMn2O6 sample and the lattice parameters undergo anisotropic changes at TC related to the orientation of the magnetic moments.
    • Tuning the tilting of the spiral plane by Mn doping in YBaCuFeO5 multiferroic

      23 April 2021 328 hit(s) Oxides
      The layered perovskite YBaCuFeO5 (YBCFO) is considered one of the best candidates to high-temperature chiral multiferroics with strong magnetoelectric coupling. In RBaCuFeO5 perovskites (R: rare-earth or Y) A-site cations are fully ordered whereas their magnetic properties strongly depend on the preparation process. They exhibit partial cationic disorder at the B-site that generates a magnetic spiral stabilized through directionally assisted long range coupling between canted locally frustrated spins.
    • New Sensitive and Selective Chemical Sensors for Ni2+ and Cu2+ Ions: Insights into the Sensing Mechanism through DFT Methods

      09 April 2021 370 hit(s) Oxides
      We report the synthesis and theoretical study of two new colorimetric chemosensors with special selectivity and sensitivity to Ni2+ and Cu2+ ions over other metal cations in the CH3CN/H2O solution. Compounds (E)-4-((2-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl)aniline (A) and (E)-4-((3-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl)aniline (B) exhibited a drastic color change from yellow to colorless, which allows the detection of the mentioned metal cations through different techniques.

    INSTITUT DE CIÈNCIA DE MATERIALS DE BARCELONA, Copyright © 2020 ICMAB-CSIC | Privacy Policy | This email address is being protected from spambots. You need JavaScript enabled to view it.