Polarization microscope studies on single crystal samples of Pb(Fe 1 /2Nb 1 / 2 )o 3 [PFN] have been made. Thin platelets (<60~) show large, homogeneous ferroelectric domains and optical characterization shows PFN is trigonal "••• at room temperature and optically negative. Birefringence measurements between 4.2K and 400K reveal the transition to the cubic structure takes place at 383K, in accordance with earlier work, but they also locate a previously undetected structural modification at 354K, accompanied simultaneously by a re-orientation of the index ellipsoid; both transitions manifest themselves by endothermic reactions on heating in DTA experiments. The new phase is very likely monoclinic.
Ferromagnetic stripe domains were observed in polarized light along the optic axes of the orthorhombic NiCl and NiBr boracites below ∼9K and ∼30K, respectively. The spontaneous magnetization vector is found to lie along the principal refractive index nγ. Measurements of spontaneous Faraday rotation and spontaneous birefringence down to 4.2K are presented
INFORMATION THEORY AS A BASIS FOR THE MAXIMUM DETERMINANTstructure-factor magnitudes are obtained from experiment. Nevertheless, the extrapolation of data, in both cases, corresponds to determination of an analytic function whose squared modulus is a function of maximum entropy measure. The definition for entropy measure is that given by Ponsonby (1973), parallel form and shown to be equivalent. With only the restrictions that (electron) density be positive, and that matrices and determinants be of small enough order to be positive definite, the two equivalent formulations yield identical results and provide an informationtheoretic interpretation of the maximum determinant.v V being the unit-cell volume. Ponsonby emphasizes that this is strictly only a measure of relative entropy of the real power spectrum of an underlying signal. In this sense maximum H' corresponds to maximum entropy measure p(r) = Ig(r)l z, and a maximum-entropy distribution function for Gh, the transform of g(r). Equation (6)
AbstractBy measuring the birefringence on (001) platelets of PAMC as a function of temperature, previously determined phase transitions have been confirmed. Large effects were measured on passing through the normal-incommensurate ~ --, y transition and through the normal-commensurate ~ --, e transition, whereas the commensurate-normal e--, 6 and the incommen-* Bis(n-propylammonium) tetrachloromanganate.
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