Jahn-Teller effects in transition metal oxides A{sub}(1-x)A'{sub}xMnO{sub}3, La{sub}(2-2x)Sr{sub}(1+2x)Mn{sub}2O{sub}7, La{sub}(1-x)Sr{sub}xCoO{sub}3, WO{sub}3

摘要

With the use of pulsed neutron diffraction and the pair density function analysis in (A{sub}(1-x)A'{sub}x){sub}(n+1)B{sub}nO{sub}(3n+1) (with A = La, Nd, and Pr, A' = Ba, Ca, and Sr, B = Co, Mn, and W, and n = 2 and ∞), the response of the lattice was measured across phase boundaries. These examples provide an opportunity for exploring static as well as dynamic type of distortions. In the CMR manganese compounds, the existence of Jahn-Teller type distortions is compatible with the particular metallic state present in these compounds. On the other hand in the cobaltates, the complex spin activations stimulate dynamical JT effects generating a glassy structure with properties that are distinctly different from those of the manganites. And finally, in the tungstates, pseudo-Jahn-Teller effects give rise to a unique local atomic structure concomitant with an order-disorder transition. These studies illustrate how significantly the local structure can deviate from the average crystallographic structure and this can critically determine the properties of the solid.