Charge-ordered phase

Intermediate phases between these two extremes can be formed. The most stable of these are Sr5Mn50i3 and Sr7Mn7019. In both of these phases the structure consists of both square pyramids, containing Mn3+ and octahedra containing Mn4+ (Fig. 9.8c and 9.8d). These structures exhibit charge ordering, but the magnetic and spin states of the Mn ions has yet to be resolved. 

FIG. 34. A sequence of STM images of a surface charge-induced transition from the disordered to the ordered phase of 2-2 bipyridine adsorbed on Au(lll). At positive charges the molecules stack into polymeric chains, which are initially disordered as shown in (A). As the potential is increased, small ordered domains begin to form and expand as the potential is increased from 0.14 to 0.25 V (B-E). The domains follow the symmetry of the Au(lll) substrate. (From Ref. 467.)... 

The switching or memory phenomena induced by electric field application or photo irradiation have been studied on Mott insulators, charge ordered insulators, and N-I transition systems and were found to be fast phase transitions in general. For the former two systems, the phase transitions caused a pronounced change in reflectance and conductivity from insulating to metallic features. The third system also exhibited a change in conductivity and dielectric response connected with the transports of solitons and/or domain walls, dynamic dimerization, and... 

The phase transition consists of a cooperative mechanism with charge-ordering, anion order-disorder, Peierls-like lattice distortion, which induces a doubled lattice periodicity giving rise to 2 p nesting, and molecular deformation (Fig. 11c). The high temperature metallic phase is composed of flat EDO molecules with +0.5 charge, while the low temperature insulating phase is composed of both flat monocations... 

Laser irradiation onto the insulating (EDO)2PF6 crystal induces a phase transition to the highly conductive state within a few picoseconds [162, 180]. The crystal surface was excited by laser irradiation with a pulse width of 0.12 ps. The excitation photon energy (1.55 eV) was nearly resonant to the CT band at 11.1 x 10 cm (1.37 eV), directly reflecting the excitation of the charge ordered state. 

Fig. 13 Generalized phase diagram for the (TMTSF)2X and (TMTTF)2X by Jerome [195]. CL, SP, SDW, and SC refer to charge-localized (which corresponds to charge-ordered state), sprn-Peierls, spin density wave, and superconducting states, respectively, (a) (TlVrrTF)2PF6, (b) (TMTTF>2Br, (c) (TMTSF)2PF6, (d) (TMTSF)2C104...

Tajima N, Sugawara N, Tamura M, Nishio Y, Kajita K (2006) Electronic phases in an organic conductor a-(BEDT-TTF)2l3 ultra narrow gap semiconductor, superconductor, metal, and charge-ordered insulator. J Phys Soc Jpn 75 051010/1-10... 

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