An Experimental Determination of Long Wave-length Phonons and Anomalous Dielectric Behavior in Proustite and Pyrargyrite
In this work, the Raman, far-infrared, dielectric and group theoretical properties of proustite (Ag3AsS3) and pyrargyrite (Ag3SbS3) were studied. The data and analyses provide information about the long wavelength lattice vibrations of these materials, as well as characterize anomalous dielectric behavior at elevated temperatures (> 250K). The Raman scattering experiments resulted in the observation of 6A(1) and 13E fundamental vibrational modes for both materials. The forward- and back-scattering Raman experiments enabled the longitudinal and transverse optic phonons to be separated (A(1)). Using these results and the Lyddane-Sachs-Teller relation, the low frequency dielectric constant was calculated. An anomalous dielectric behavior at elevated temperatures was attributed to silver ionic conduction in the material and not to a lattice mechanism (ferroelectric phase transition). A model was proposed in which the differences in conductivities of the bulk and space-charge/interface region lead to an interfacial polarization and concomitant rise in the dielectric constant.
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INCIDENT OPTICS OF LASER RAMAN SETUP
RIGHT ANGLE 90 SCATTERING CONFIGURATION
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angle anomalous dielectric behavior applied atoms av(xz axes beam BREAKS IN SPECTRUM c-axis calculated capacitance Cartesian coordinate CHANGE OF SCALE Chapter character tables characterized curves degenerate degrees of freedom diagonal dielectric anomaly dielectric constant electric field experimental factor group far-infrared ferroelectric ferroelectric phase transition force constants Fourier transform given gives glide plane group theoretical incident instrument INTERFERENCE FIGURE internal coordinates ionic irreducible representation laser lattice vibrations lens linear LO-TO low frequency LST relation materials matrix representation melatope normal coordinates normal modes obtained optic axis oscillations perpendicular phonon point group polariton polarizability polarization proustite and pyrargyrite PROUSTITE SAMPLE pyramids radiation Raman lines Raman scattering RAMAN SPECTRUM rays respect rotation sample holder SCATTERING CONFIGURATION secular equation shown in Figure silver ions slit solution spectra spectrometer SPECTRUM INDICATE CHANGE SPECTRUM OF PROUSTITE stretching structure symmetry coordinates symmetry type tion unit cell wave vector