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  • 1
    Electronic Resource
    Electronic Resource
    Charge transport in lithium phthalocyanine (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5048-5053 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ac electrical properties of monoclinic lithium phthalocyanine (LiPc) and of the iodinated compound LiPcI have been investigated in the frequency and temperature regimes 20 Hz≤ν≤1 GHz and 1.5 K≤T≤300 K, respectively. Both compounds are semiconductors with dielectric constants ε∞≈6 (LiPc) and 20 (LiPcI). Up to room temperature tunneling of charge carriers is the dominant conduction process in both compounds, yielding intrinsic dc conductivities σdc≈5.3×10−4 Ω−1 cm−1 (LiPc) and 0.2 Ω−1 cm−1 (LiPcI). The frequency and temperature dependence of the complex ac conductivity suggests polarons as the dominant species of charge carriers. The higher conductivity of the iodinated compound can be attributed to an enhanced mobility of the polaronic charge carriers which is most probably due to a better overlap of the π orbitals along the stacking direction of the molecules. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471134
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular reorientation in ortho-carborane studied by dielectric spectroscopy (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4324-4329 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dielectric properties of ortho-carborane have been investigated in a broad frequency range of 20 Hz≤ν≤1 GHz and at temperatures 10 K≤T≤380 K. At T(approximately-greater-than)275 K the ortho-carborane molecules undergo fast and isotropic reorientations with frequencies larger than 1 GHz. Below a phase transition at Tc≈275 K the reorientation is partly restricted and the dynamics of the remaining reorientational motion is reduced. At 160 K, the dielectric results reveal a small anomaly which we assign to a second phase transition. At temperatures 150 K〈T〈275 K the dipolar active orientational degrees of freedom freeze in on the time scale of the measuring frequencies. The corresponding peaks in the frequency dependence of the dielectric loss can well be described using the Fourier transform of the Kohlrausch–Williams–Watts (KWW) function with a stretching parameter β≈0.8. However, for frequencies well above the peak maximum we find significant deviations from KWW behavior. In the temperature and frequency range investigated, the dynamics of the dipolar relaxation process behaves thermally activated with an activation energy of 0.52 eV. In the classification scheme of Angell et al. the fragility of ortho-carborane can be estimated as m≈20 characterizing it as a strong glass former. Ortho-carborane fits well into the correlation scheme of Böhmer et al. where polydispersivity and fragility are related to each other. At high temperatures and low frequencies conductivity processes (hopping) dominate the dielectric response of ortho-carborane. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471242
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic and structural transitions in La1−x Sr x MnO3: T-x phase diagram (1998)
    Springer
    JETP letters 68 (1998), S. 356-362 
    Details
    ISSN: 1090-6487
    Keywords: 75.30.Kz ; 61.50.Ks ; 72.20.My ; 75.50.Dd
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electrical conductivity, magnetic susceptibility, magnetization, and submillimeter (v=5∓20 cm−1) permittivity and dynamic conductivity of La1−x Sr x MnO3 (0≤x≤ 0.45) single crystals are investigated. The anomalies in the temperature dependences of these quantities are identified with diverse magnetic and structural phase transformations, including antiferromagnetic and ferromagnetic ordering, structural transitions between strongly distorted (Jahn-Teller) and weakly distorted (pseudocubic) orthorhombic phases, structural transitions to a rhombohedral phase and unusual transitions to a polaron-ordering state. As a result, the complete T-x phase diagram of the system La1−2x Sr x MnO3 is constructed in a wide interval of temperatures T=4.2∓1050 K and concentrations x=0−0.45.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567873
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  • 4
    Electronic Resource
    Electronic Resource
    Low-Frequency Relaxation Rate in the Superconducting YBa2Cu3O6.7 (1999)
    Springer
    Journal of low temperature physics 117 (1999), S. 1043-1047 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The submillimeter-wave 3 cm −1 〈 ν 〈 40 cm −1 complex conductivity of the reduced YBa 2 Cu 3 O 6.7 film, (T C =56.5 K) was investigated for temperatures 4 K 〈 T 〈 300 K. The frequency dependence of the effective quasiparticle scattering rate 1/τ*(ν) was extracted from the spectra. 1/τ* is shown to be frequency independent at low frequencies and high temperatures. On decreasing temperature the scattering rate increases with increasing frequencies. Finally, at 6 K it follows a power-law, 1/τ* ∝ ν1.75±0.3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022518122120
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic susceptibility, heat capacity, and optical conductivity of LiPc and LiPcI (1998)
    Springer
    The European physical journal 6 (1998), S. 317-322 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 76.30.-v Electron paramagnetic resonance and relaxation - 72.80.Le Polymers; organic compounds (including organic semiconductors) - 75.40.-s Critical-point effects, specific heats, short-range order
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The magnetic susceptibility, using dc and electron spin resonance (ESR) methods, the specific heat, and the infrared properties of the one-dimensional molecular semiconductors lithium phthalocyanine (LiPc) and the iodinated compound LiPcI have been investigated for temperatures K. LiPc has a half-filled conduction band and is expected to be an organic metal. However, due to the strong Coulomb repulsion the system is a one-dimensional Mott-Hubbard insulator with a Hubbard gap of 0.75 eV as inferred from optical measurements. The localized electrons along the molecular stacks behave like a S = 1/2 antiferromagnetic spin chain. The spin susceptibility, as determined by ESR experiments, and the magnetic contribution to the heat capacity show a Bonner-Fisher type of behavior with an exchange constant K. LiPcI is an intrinsic narrow-gap semiconductor with an optical gap of 0.43 eV. In ESR experiments it is silent, indicating that all the unpaired electrons have been removed from the macrocycle via doping with iodine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050555
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  • 6
    Electronic Resource
    Electronic Resource
    Intrinsic Electron Paramagnetic Resonance in La2−xSrxCuO4: Manifestation of Three Spin Polarons (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 57-59 
    Details
    ISSN: 1572-9605
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Electron-Paramagnetic-Resonance (EPR) measurements on La2−x Sr x CuO4single crystals provide experimental evidence of a three-spin polaron of twoCu2+ ions and one p hole. The symmetry properties and the peculiartemperature dependence of the g-value of the EPR line indicate the presenceof a dynamical Jahn–Teller distortion (Q 2-mode) and formation of acollective mode of polarons and surrounding strongly correlated Cu ions(bottleneck regime).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007717518935
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