scholarly journals Perovskite Crystals: Unique Pseudo-Jahn–Teller Origin of Ferroelectricity, Multiferroicity, Permittivity, Flexoelectricity, and Polar Nanoregions

2020 ◽  
Vol 5 (4) ◽  
pp. 68
Author(s):  
Isaac B. Bersuker ◽  
Victor Polinger
Keyword(s):  
Transition Metal ◽  
Self Assembly ◽  
Dipole Moments ◽  
Electronic States ◽  
Opposite Parity ◽  
Hindered Rotation ◽  
Orientational Polarization ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Polar Nanoregions

In a semi-review paper, we show that the local pseudo-Jahn–Teller effect (PJTE) in transition metal B ion center of ABO3 perovskite crystals, notably BaTiO3, is the basis of all their main properties. The vibronic coupling between the ground and excited electronic states of the local BO6 center results in dipolar distortions, leading to an eight-well adiabatic potential energy surface with local tunneling or over-the-barrier transitions between them. The intercenter interaction between these dipolar dynamic units results in the formation of the temperature-dependent three ferroelectric and one paraelectric phases with order–disorder phase transitions. The local PJTE dipolar distortion is subject to the presence of sufficiently close in energy local electronic states with opposite parity but the same spin multiplicity, thus limiting the electronic structure and spin of the B(dn) ions that can trigger ferroelectricity. This allowed us to formulate the necessary conditions for the transition metal perovskites to possess both ferroelectric and magnetic (multiferroic) properties simultaneously. It clarifies the role of spin in the spontaneous polarization. We also show that the interaction between the independently rotating dipoles in the paraelectric phase may lead to a self-assembly process resulting in polar nanoregions and relaxor properties. Exploring interactions of PJTE ferroelectrics with external perturbations, we revealed a completely novel property—orientational polarization in solids—a phenomenon first noticed by P. Debye in 1912 as a possibility, which was never found till now. The hindered rotation of the local dipole moments and their ordering along an external field is qualitatively similar to the behavior of polar molecules in liquids, thus adding a new dimension to the properties of solids—notably, the perovskite ferroelectrics. We estimated the contribution of the orientational polarization to the permittivity and flexoelectricity of perovskite crystals in different limiting conditions.

scholarly journals Bond-Length Distributions for Ions Bonded to Oxygen: Results for the Transition Metals and Quantification of the Factors Underlying Bond-Length Variation in Inorganic Solids

2020 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Transition Metal ◽  
Bond Length ◽  
A Priori ◽  
Bond Formation ◽  
Length Variation ◽  
Electronic Effects ◽  
Coordination Polyhedra ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Non Local

Bond-length distributions are examined for 63 transition-metal ions bonded to O2- in 147 configurations, for 7522 coordination polyhedra and 41,488 bond distances, providing baseline statistical knowledge of bond lengths for transi-tion metals bonded to O2-. A priori bond valences are calculated for 140 crystal structures containing 266 coordination poly-hedra for 85 transition-metal ion configurations with anomalous bond-length distributions. Two new indices, Δ𝑡𝑜𝑝𝑜𝑙 and Δ𝑐𝑟𝑦𝑠𝑡, are proposed to quantify bond-length variation arising from bond-topological and crystallographic effects in extended solids. Bond-topological mechanisms of bond-length variation are [1] non-local bond-topological asymmetry, and [2] multi-ple-bond formation; crystallographic mechanisms are [3] electronic effects (with inherent focus on coupled electronic-vibra-tional degeneracy in this work), and [4] crystal-structure effects. The Δ𝑡𝑜𝑝𝑜𝑙 and Δ𝑐𝑟𝑦𝑠𝑡 indices allow one to determine the primary cause(s) of bond-length variation for individual coordination polyhedra and ion configurations, quantify the dis-torting power of cations via electronic effects (by subtracting the bond-topological contribution to bond-length variation), set expectation limits regarding the extent to which functional properties linked to bond-length variations may be optimized in a given crystal structure (and inform how optimization may be achieved), and more. We find the observation of multiple bonds to be primarily driven by the bond-topological requirements of crystal structures in solids. However, we sometimes observe multiple bonds to form as a result of electronic effects (e.g. the pseudo Jahn-Teller effect); resolution of the origins of multiple-bond formation follows calculation of the Δ𝑡𝑜𝑝𝑜𝑙 and Δ𝑐𝑟𝑦𝑠𝑡 indices on a structure-by-structure basis. Non-local bond-topological asymmetry is the most common cause of bond-length variation in transition-metal oxides and oxysalts, followed closely by the pseudo Jahn-Teller effect (PJTE). Non-local bond-topological asymmetry is further suggested to be the most widespread cause of bond-length variation in the solid state, with no a priori limitations with regard to ion identity. Overall, bond-length variations resulting from the PJTE are slightly larger than those resulting from non-local bond-topological asym-metry, comparable to those resulting from the strong JTE, and less than those induced by π-bond formation. From a compar-ison of a priori and observed bond valences for ~150 coordination polyhedra in which the strong JTE or the PJTE is the main reason underlying bond-length variation, the Jahn-Teller effect is found not to have a symbiotic relation with the bond-topo-logical requirements of crystal structures. The magnitude of bond-length variations caused by the PJTE decreases in the fol-lowing order for octahedrally coordinated d0 transition metals oxyanions: Os8+ > Mo6+ > W6+ >> V5+ > Nb5+ > Ti4+ > Ta5+ > Hf4+ > Zr4+ > Re7+ >> Y3+ > Sc3+. Such ranking varies by coordination number; for [4], it is Re7+ > Ti4+ > V5+ > W6+ > Mo6+ > Cr6+ > Os8+ >> Mn7+; for [5], it is Os8+ > Re7+ > Mo6+ > Ti4+ > W6+ > V5+ > Nb5+. We conclude that non-octahedral coordinations of d0 ion configurations are likely to occur with bond-length variations that are similar in magnitude to their octahedral counterparts. However, smaller bond-length variations are expected from the PJTE for non-d0 transition-metal oxyanions.<br>

Cooperative Pseudo Jahn-Teller Effect as Microscopic Mechanism of (OMT)-(LTT) Structural Phase Transition in La2−xBaxCuO4Superconductors

1992 ◽  
Vol 291 ◽  
Author(s):  
Michael D. Kaplan
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Electronic States ◽  
Teller Effect ◽  
Excited Electronic States ◽  
Microscopic Mechanism ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Local Distortions

ABSTRACTA microscopic mechanism for the structural phase transition from the orthorhombic mediate temperature (OMT) phase into the low temperature tetragonal (LTT) one is suggested on the basis of the cooperative pseudo Jahn-Teller effect. The local distortions mixing the ground and the first excited electronic states are ordered antiferrodistortively and are connected in part, with the oxygen octahedra rotations around the [100] axis. The results are in agreement, with the neutron scattering experiments data.

scholarly journals The Jahn–Teller effect in the presence of partial isotopic substitution: the B̃1E′′ state of NH2D and NHD2

2015 ◽  
Vol 17 (21) ◽  
pp. 14145-14158 ◽  
Author(s):  
Ashim Kumar Saha ◽  
Gautam Sarma ◽  
Chung-Hsin Yang ◽  
Sebastiaan Y. T. van de Meerakker ◽  
David H. Parker ◽  
...  
Keyword(s):  
Force Field ◽  
Field Model ◽  
Electronic States ◽  
Teller Effect ◽  
Isotopic Substitution ◽  
Quadratic Force Field ◽  
Jahn Teller ◽  
Jahn Teller Effect

A simple linear and quadratic force field model for the lifting of the degeneracy on asymmetric isotopic substitution in degenerate electronic states subject to a weak Jahn–Teller effect.

scholarly journals Effect of Metal on the Properties of the Azopyridine Complexes of Iron, Ruthenium and Osmium

2019 ◽  
pp. 1-16
Author(s):  
Ouattara Wawohinlin Patrice ◽  
Bamba Kafoumba ◽  
N’guessan Nobel Kouakou ◽  
Koné Mamadou Guy Richard ◽  
Kodjo Charles Guillaume ◽  
...  
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Dipole Moments ◽  
Angular Variation ◽  
Functional Theory ◽  
Anti Cancer ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Ru Complexes ◽  
The Ideal

The theoretical study of α-, β-, γ-, δ-, ε- MCl2(Azpy)2 isomers with (M = Fe, Os and Ru) complexes is carried out using Density Functional Theory (DFT) at the B3LYP / LANL2DZ level. This study is focused not only on the effect of metals over geometric, electronic and reactivity parameters, but also on their anti-cancer effect. Its results that the geometric parameters undergo small modifications. These modifications evolve from iron to osmium through ruthenium complexes. Thus, the lengths of the bonds M-X (with X = Cl, N2, Npy) follow the following order Fe-X <Ru-X <Os-X. However, regarding their angular variation that undergoes deformation through the octahedron shape, it could be related to Jahn Teller effect. Also, the substitution of Ru by Os would increase the reactivity of these complexes. Among the isomers studied, the ε-Fe, δ-Ru and δ-Os complexes are likely to bind easily to the DNA. The values of the dipole moments are arranged in the following order: μ (ε-M)> μ (β-M)> μ (α-M)> μ (γ-M)> μ (δ-M) within these azopyridine complexes. Finally, we notice that the substitution of Ru by Os improves the cytotoxicity and the fluorescence of these complexes. The δ-Os isomer has the best cytotoxic and photosensitive characteristics of these azopyridine complexes and would be the ideal isomer for the diagnosis and treatment of cancers.

Sign in / Sign up

Export Citation Format

Share Document