Are antiferroelectricity and other physical properties 'hidden' in spinel compounds?

Abstract

Abstract. The piezoelectric switching of antiferroelectric domains by the simultaneous application of an electric field Ei and mechanical stress Tk is proposed as a direct method for examining whether some spinel compositions do have point symmetry 33m and concomitant antiferroelectric ordering as proposed by Grimes.For piezoelectric antiferroelectrics, the switching energy is Ag = 2dij,Ei7;, (d,,, = piezoelectric coefficient). For point symmetry 43m, various possible switching procedures have been described in detail. The smallest coercive product of electric field and stress (E,T,k), is required for switching when the electric field is chosen along cubic [OOl], and directional stress along [llO] or [lTO]. For particular directions, for example [lll], the colinear application of electric field and stress also leads to switching.If the assumed prototype with space group F33m -t h e symmetry proposed by Grimesis supposed to undergo a phase transition leading to ferrimagnetism, the possible symmetries ofthe ferrimagnetic domains are given by the magnetic groups 14m'2', Im'm2 and R3m'. which are M-maximal subgroups of the prototype magnetic group Fz3ml'. All three ferrimagnetic phases permit piezoelectricity, piezomagnetism and the linear and second-order magnetoelectric effect. The tetragonal phase (15m'27 remains antiferroelectric as the prototype is supposed to be, whereas the orthorhombic (Im'm27 and trigonal (R3m') phases become ferroelectric. The full lattice of subgroups of FiT3ml' is presented.

Polar phonons and spin-phonon coupling inHgCr2S4andCdC

“…5 display the generalized LST relation for the static dielectric constant as calculated via Eq. (12). Within 2 % these relations remain constant for all modes.…”

“…11 However, the origin of these polar distortions is unclear 12 and in ab initio phonon calculations 13 no indications for a structural instability due to soft phonon modes have been detected. Recently, evidence accumulates that the large magnetocapacitive (MC) effects in the chromium spinels strongly depend on thermal treatment and/or doping.…”

Polar phonons and intrinsic dielectric response of the ferromagnetic insulating spinelCdCr2S4from first principles

“…The possibility of this phase transition of this type has been the subject of previous speculation (but never experimentally demonstrated) for many spinels. 23,45 Our calculation reveals that both A 2u modes are quite hard with frequencies greater than 300 cm −1 . In addition, the frequencies of the other silent zone-center phonon modes, E u , T 1g , and T 2u , were all calculated to be greater than 100 cm −1 .…”

Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations

“…The question of whether known nonpolar structure families could have representatives with polar instabilities has proved to be perennially fascinating, especially with regard to spinels and pyrochlores [64][65][66]. To choose a distinct nonpolar structure type for the present study, we searched ICSD for ternary antimony oxides, the main group element Sb being, as in the previous section, selected to promote a lower band gap in the hope of discovering new ferroelectric semiconductors.…”