Showing papers by "Anvar A. Zakhidov published in 1996"

Organic photovoltaic cell with donor-acceptor double heterojunctions

Abstract: An organic photocell, which has a multilayer structure consisting of poly(2,5-dioctyloxy-p-phenylenvinylene) (OOPPV)/octaethylporphine (OEP)/backminsterfullerene (C60), has been fabricated. The photocurrent yield spectra are measured in terms of the light absorption in the OEP layer, the exciton migration and the charge generation at both organic heterojunctions. That is, the double heterojunctions OOPPV/OEP and OEP/C60 contribute to the charge generation by excitonic dissociation. The mechanisms of charge generation and photocurrent enhancement are discussed taking the energy band structure and photoinduced charge transfer into consideration.

A search for new ionic C60 charge transfer complexes

Abstract: As one of the strategies to obtain ionic C60 charge transfer complexes, a doping of alkali metals to neutral CT complexes has been attempted under a mild condition. Superconductivity has been detected by magnetic measurements in OMTTF·C60·benzene doped with potassium or rubidium, where OMTTF is octamethylene-tetrathiafulvalene.

Multiphase superconductivity in OO-PPV/C60 composite doped by alkali metals low-field microwave absorption and SQUID study

Abstract: Superconducting (SC) phases in poly(2,5-dicotyloxy-p-phenylene vinylene) (OO-PPV) composite with fullerene C60 are found upon alkali-metal A ( = K and Rb) vapor doping by sensitive low-field microwave absorption (LFMA) and proved by SQUID. LFMA of OO-PPV(C60)yKx at small y < 0.0005 shows a “normal out-of-phase” shape, and appears at Tc = 11 K. At larger C60 content 0.01 < y < 0.1, the LFMA revealed unusual multipeak spectra, with two components appearing at different Tc's. At Tc1 = 12–13 K for K dopant (and Tc1 = 21.5 K for Rb) the broad component appears with anomalous phase, which we assign to SC A3C60 grains weakly linked into Josephson media, containing π junctions. By SQUID measurements the paramagnetic Meissner effect has been observed, supporting the existence of π junctions. Below Tc2 = 6.5–8.5 K (for K) and Tc2 = 11 K (for Rb) the narrow component with a normal phase and hysteresis appeared in the LFMA spectra. The structure found by SQUID measurements at the same Tc2 supports this assignment to a second SC2 phase. One possible origin of SC2 is discussed in terms of nonstoichiometric AxC60 grains (with x ≠ 3), and C60 induced superconductivity, in which electrons of conducting polymer chains are actively involved in SC pairing via hybridization with C60 may be another origin for SC2. Alternative explanations for multipeaked LFMA are also discussed.

Overview of 10K Class Organic Superconductors κ-(BEDT-TTF)2X (X = Cu (NCS)2, Cu(CN)[N(CN)2], Cu[N(CN)2]X′ (X′ = Cl, Br) and a Search for Superconductivity in Alkali Doped C60 Complexes

Abstract: The curious structural and, physical properties of the 10K class BEDT-TTF superconductors having polymerized anions and the superconductivity of the alkali doped C60 organic CT complexes are described.

A new metastable superconductor Li2Na1NyC60 prepared from azides

Abstract: A new metastable superconductor with nominal composition of Li 2 Na 1 N y C 60 ( y unknown) is prepared by thermal decomposition of lithium azide (LiN 3 ) and sodium azide (NaN 3 ). It is suggested that the superconducting phase in this compound is created by intercalation of the neutral spacer such as NaN 3 . The supeconductivity is examined by a low-field signal of microwave absorption (LFS) and by SQUID. The critical temperature is estimated to be 12 K from SQUID and 14 K from LFS measurement, and the shielding fraction is over 9% at 5 K. Superconducting parameters, such as critical temperature, upper and lower critical fields, coherence length and penetration depth are evaluated and found to be distinct from those in other fulleride superconductors.

ESR study of high-pressure phases of C60 fullerene

Abstract: Face-centered cubic and rhombohedral phases of pressure-temperature treated C 60 were investigated by ESR spectroscopy in the 5 to 550 K temperature range. It was found that the ESR spectra of the former differ only slightly from those of the starting C 60 powder. The intensity of the ESR signal from this phase reduces upon heating the specimens above 480 K. In contrast, the rhombohedral phase shows an intense narrow ESR line which obeys the Curie law and does not change much upon heating. The origin of paramagnetic centers in the high-pressure phases of C 60 and their relationship to the structure of the substances are discussed.

Alkali metal doping to c60 ct complexes

Abstract: In order to ionize C60 in a different packing manner other than A3C60, alkali metals were doped to neutral charge transfer complexes under a mild condition. Bulk superconductivity has been detected by magnetic measurements in OMTTF·C60·benzene doped with potassium or rubidium, where OMTTF is octamethylene-tetrathiafulvalene. Although an expansion of unit cell volume has been observed in the case of the potassium doping, such a detection of apparent change in the single crystal x-ray diffractometry has not succeeded yet by the rubidium doping. After the x-ray experiments on the rubidium-doped crystals, however, SQUID measurements showed superconductivity in one crystal out of the three examined.