Electrical asymmetry, degree

Practical applications in which copolymers are characterized by some degree of structural asymmetry have been suggested. For instance, a flexible block may be chosen because it donates a flexural compliance, whereas the more rigid portion offers tensile strength. In addition to the mechanical properties, the orientational order and the electrical conductance of certain rigid blocks could be exploited in optical and electrical devices. 

Because the value of the excited-state quadrupole moment of the Sn nucleus is not well established, the actual values of the electric field gradients cannot be derived from the observed quadrupole splitting. We cannot say therefore what degree of asymmetry of 5p-orbital occupancy is indicated, or what the upper limit of quadrupole splitting for an asymmetric environment is likely to be (the maximum value known to date is 5-54 mm s in McjSnCSOalOj in which the tin atom is probably 6-coordinated with bridging 0-S0(F)-0 groups [133]. 

Orbital degrees of freedom are one of the important parameters to discuss the ordered ground states in materials. Orbital occupancy reflects electric field gradient (EFG) at nuclei. Then, Mossbauer spectroscopy can detect orbital occupancy of electrons, especially d or f electron cases. Electronic orbits in f electrons are usually called electronic quadrupole moments. Electronic quadrupole moments directly interact with nuclear quadrupole moments, which are observed as nuclear quadrupole interactions. Since the nuclear quadrupole moment in the Mossbauer transition is relatively large, 3.1 barn, the nuclear quadrupole interaction is relatively easy to detect as asymmetry of spectra even when hyperfine fields are observed. 

As outlined in section 1.3.2., the nuclear quadrupole interaction is characterized by two parameters, the coupling constant eQVz expressed in suitable energy units, and an asymmetry parameter tj indicating the degree of departure of the electric field gradient (efg) tensor Fy from axial symmetry. Information relevant to the lanthanide-containing metal, alloys, or compound is contained in these two parameters, since from the standpoint of the physics or chemistry of solids the quadrupole moment Q is taken to be a known property of the nuclear state. 

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