Impurities in Noncubic Crystals: Stabilization Mechanisms for Jahn-Teller Ions in Layered Perovskites

Abstract

Mechanisms responsible for the local geometry around Jahn-Teller impurities in K2NiF4 type lattices are shown to be different from those generating the warping in cubic crystals. The present density functional theory calculations reveal that the elastic anisotropy of the host lattice (visible for closed shell impurities) and the electric field created by the rest of lattice ions upon active electrons make it possible to have d(9) ions in an elongated geometry but with a A(1g) ground state. The puzzling difference between equilibrium geometries for Cu2+ and Ni+ in layered perovskites can reasonably be understood.

Coherent tunneling inCu2+- andAg2+-doped MgO andGarcía‐Fernández1, Sousa2, Aramburu3 et al. 2005Phys. Rev. BSelf Cite272250View full textAdd to dashboardCite

“…The present results, together with those recently obtained on layered perovskites, 23 stress the importance of ab initio calculations for gaining a better insight into the subtle phenomena related to the JT effect. This is particularly true as regards the barrier energy, B, on which the experimental information is certainly scarce.…”

“…10,17,23 This leads to an impurity-ligand distance, R oct , different from R 0 corresponding to the perfect host lattice. In DFT an electronic density displaying cubic symmetry can easily be built for a d 9 impurity through the ͑3z 2 − r 2 ͒ 1.5 ͑x 2 − y 2 ͒ 1.5 configuration.…”

“…In DFT an electronic density displaying cubic symmetry can easily be built for a d 9 impurity through the ͑3z 2 − r 2 ͒ 1.5 ͑x 2 − y 2 ͒ 1.5 configuration. 10,17,23 In a second step, adiabatic calculations are carried out for both…”

Internal electric fields and color shift in Cr3+-based gemstones

“…32,34 Furthermore, it has been shown that E R (r) plays a key role for understanding the local structure and the associated spectroscopic properties of Cu 2+ -and Cr 3+ -doped layered perovskites such as K 2 AF 4 (A = Mg, Zn). 39 Despite that the mere addition of the internal electric field E R (r) to the CrO 6 9− complex allows one to understand an important number of experimental facts corresponding to the Cr 3+ -based gemstones, there is, however, a fundamental question which needs to be answered. As it has been pointed out, the internal electric field E R (r) will modify the electronic density and covalency inside the CrO 6 9− unit provided V R (r) is not a constant on the whole complex region.…”

A Study of Spin-Hamiltonian Parameters and Defect Structure for Co2+ Ion in the Tetragonal Zn2+ Site of Ba2ZnF6 Crystal

“…A similar case can also be found for Cu 2+ in K 2 MgF 4 crystal. The density functional theory (DFT) calculations [30,44] reveal that the octahedral environment of Cu 2+ in K 2 MgF 4 is tetragonallycompressed. This point is also unlike the corresponding octahedron in the host crystal K 2 MgF 4 , but in agreement with that in the isomorphous pure crystal K 2 CuF 4 [45].…”