Dynamics of antipolar distortions

Patel, Kinnary; Prosandeev, Sergey; Bellaïche, L.

doi:10.1038/s41524-017-0033-z

Cited by 6 publications

(7 citation statements)

References 48 publications

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“…Such a unusual mixed behavior originates from the ω R xȳ ω M z z u Xz A,xȳ coupling, as also previously found in Ref. [43] . It is also worthwhile to indicate that Ref.…”

Section: Structural Distortions In Orthorhombic Perovskitessupporting

confidence: 85%

Energetic Couplings in Ferroics

Zhao

Chen

Prosandeev

et al. 2021

Adv Elect Materials

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Ferroics include diverse degrees of freedom (such as structural distortions and magnetic moments) among which cross couplings occur, rendering a large variety of interesting phenomena. Determining such couplings, based on symmetry analysis, is not only important to interpret observed phenomena but can also result in novel predictions to be then experimentally checked. Often, such energetic couplings are difficult to construct without a deep knowledge of group theoretical symmetry principles. In the present review, a crash course towards the derivation of energetic couplings, without using much the group theoretical language, is provided. Rather, the present approach relies on a graphical technique and suitable symbolic language, which naturally yields some known couplings (resulting in, e.g., spin/dipole canting, magnetically driven polarization and antipolar/antiferroelectric states). This review also reports and discusses other symmetry-allowed energetic terms, including some leading to the occurrence of an electric polarization in a variety of materials, and "exotic" ones that generate complex phases and phenomena in, e.g., nanostructures and heterostructures.

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“…Such a unusual mixed behavior originates from the ω R xȳ ω M z z u Xz A,xȳ coupling, as also previously found in Ref. [43] . It is also worthwhile to indicate that Ref.…”

Section: Structural Distortions In Orthorhombic Perovskitessupporting

confidence: 85%

Energetic Couplings in Ferroics

Zhao

Chen

Prosandeev

et al. 2021

Adv Elect Materials

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“…Note that such exploration of different minima with time within the macroscopic P4 / mbm state is also numerically found for BiFeO 3 under hydrostatic pressure (not shown here), for which an intermediate P4 / mbm phase exists in a narrow temperature region too. [ 18 ] Also note that sub‐THz values of frequency, as those for v Rx , LF , P 4/ mbm in Figure 6c, are typically associated with jump between different minima, as found for the so‐called central mode of BaTiO 3 , and are typically relaxational modes. [ 37–39 ]…”

Section: Resultsmentioning

confidence: 86%

“…As derived in ref. [18], the Newtonian equation of motion thus takes the following form:

\begin{matrix} \begin{matrix} \underset{β}{140%true \sum} [{(2 π υ_{α}^{X})}^{2} - {(2 π υ)}^{2} - 2 i Γ_{α}^{X} π υ + B_{X_{α} M_{β}} 〈 ω_{M, β}^{2} 〉 + B_{X_{α} R_{β}} 〈 ω_{R, β}^{2} 〉] u_{X, α} \\ = - D 〈 ω_{M, z} 〉 〈 ω_{R, α} 〉 - D 〈 ω_{R, α} 〉 δ ω_{M, z} - D 〈 ω_{M, z} 〉 δ ω_{R, α} \end{matrix} \end{matrix}

where α = x or y , δω M , z and δω R ,α refer to the fluctuations of ω M , z and ω R ,α with respect to their spontaneous 〈ω M , z 〉 and 〈ω R ,α 〉 values.

υ_{α}^{X}

is the natural (bare) frequency of the antipolar mode,

{normalΓ}_{α}^{X}

represents

γ_{α}^{X} / m^{X}

where m X is the mass of the antipolar mode and

γ_{α}^{X}

is a damping constant.…”

Section: Resultsmentioning

confidence: 99%

“…the antiphase and in‐phase iodine octahedral tiltings ω R , ω M but also the antipolar u X mode, were considered for CsPbI 3 , as a function of temperature. Such response data were further fitted with a sum of damped harmonic oscillators (DHO) model, [ 18 ] which, for example, allowed to extract resonant frequencies.…”

Section: Methodsmentioning

confidence: 99%

“…For instance, what to expect for the temperature behavior of resonant frequencies associated with in‐phase and antiphase tiltings, as well as with antipolar motions, in materials exhibiting such intermediate dynamically averaged P4 / mbm phase (which we will refer to as scenario 1) and for which the P4 / mbm state likely has only a narrow temperature range, as in BiFeO 3 under hydrostatic pressure? [ 18 ] How do such behaviors contrast with those in materials for which, in addition to

P m \bar{3} m

and Pnma , there is an intermediate P4 / mbm phase too but that is static rather than dynamic (i.e., the system basically stays in P4 / mbm at any time), such as (K x Na 1− x )MgF 3 perovskites that has a large P4 / mbm temperature range for some compositions? [ 19 ] This situation will be referred to as scenario 2 here.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Finite‐Temperature Dynamics in Cesium Lead Iodide Halide Perovskite

Wang

Patel

Prosandeev

et al. 2021

Adv Funct Materials

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Lattice dynamics are often regarded as signatures of the underlying crystal structure. Here, a first‐principle‐based effective Hamiltonian method combined with molecular dynamics simulations is used to study dynamical behaviors of CsPbI3 perovskite across temperature and structural phase transitions. A single (short‐range tilting) parameter in this effective Hamiltonian is varied in order to make the temperature range of the intermediate tetragonal P4/mbm phase, existing in‐between the cubic Pmtrue3¯m and orthorhombic Pnma phases, either broader than observed or completely disappearing. Comparing the dynamics of these different cases allows one to conclude that real CsPbI3 perovskite should have i) two iodine‐octahedral‐tilt related modes that differ in frequency but both significantly soften as the temperature decreases within the cubic phase toward the Pmtrue3¯m‐to‐P4/mbm transition; and ii) one mode that maintains a very low frequency (of the order of 1.0 cm−1) in the entire region of P4/mbm stability, as a result of the temporal exploration of various structural states. Such latter sub‐THz mode mixes fluctuations of antiphase iodine tiltings and Cs antipolar motions because of a trilinear energetic coupling.

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