Transition from polaronic to itinerant electronic

The compositional dependence of the structural O -O transition at 7jt and the 0 -R transition at Tor can be clearly followed by monitoring the temperature dependence of the resistance (Mandal et al., 2001) monitoring the variation with x of the higher-order transition at T from the resistance curve R(T) is more subtle and has been accomplished with further aid from the thermoelectric power a(T) measured on single crystals (Zhou and Goodenough, 2000). The transition from polaronic to itinerant electronic behavior in the paramagnetic R-rhombohedral phase has not been studied. 

Zhao et al. [145-147] were the first to show a dramatic decrease of Tc on the exchange of for If on cooling through Tc the transition was from a global polaronic phase with th > to a global itinerant-electron phase with Xh then the exchange of for 0, which decreases... 

It means that for electrons which satisfy condition of extreme nonadiabaticity (antiadiabaticity with respect to interacting phonon mode r in particular direction of reciprocal lattice where the gap in one-electron spectrum has been opened), the electron (nonadiabatic polaron)-renormalized phonon interaction energy equals zero. Expressed explicitly, in the presence of external electric potential, dissipation-less motion of relevant valence band electrons (holes) on the lattice scale can be induced at the Fermi level (electric resistance p = 0). At the same time, the motion of nuclei remains bound to circumferential revolution over distorted, energetically equivalent, configurations. The electrons move in a form of itinerant-mobile bipolarons, i.e. as a polarized cloud of inter-site charge density distribution- sequence b, d, e, f, b, d, e, f. in Fig. 27.6. For temperature increase, thermal excitations of valence band electrons to conduction band induce sudden transition from the antiadiabatic state to adiabatic state at T — 7, i.e. < AEd Rd) holds and the system is... 

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