|dc.description.abstract||Using the Physical Vapor Transport method, single crystals of Cd2Re207 have been grown, and
crystals of dimensions up to 8x6x2 mm have been achieved.
X-ray diffraction from a single crystal of Cd2Re207 has showed the crystal growth in the (111)
plane. Powder X-ray diffraction measurements were performed on ^^O and ^^O samples, however no
difference was observed. Assigning the space group Fd3m to Cd2Re207 at room temperature and
using structure factor analysis, the powder X-ray diffraction pattern of the sample was explained
through systematic reflection absences.
The temperatiure dependence of the resistivity measurement of ^^O has revealed two structural
phase transitions at 120 and 200 K, and the superconducting transition at 1.0 K.
Using Factor Group Analysis on three different structiures of Cd2Re207, the number of IR and
Raman active phonon modes close to the Brillouin zone centre have been determined and the results
have been compared to the temperature-dependence of the Raman shifts of ^^O and ^*0 samples. After
scaling (via removing Bose-Einstein and Rayleigh scattering factors from the scattered light) all
spectra, each spectrum was fitted with a number of Lorentzian peaks. The temperature-dependence
of the FWHM and Raman shift of mode Eg, shows the effects of the two structurjil phase transitions
The absolute reflectance of Cd2Re207 - '^O single crystals in the far-infrared spectral region
(7-700 cm~^) has been measured in the superconducting state (0.5 K), right above the superconducting
state (1.5 K), and in the normal state (4.2 K).
Thermal reflectance of the sample at 0.5 K and 1.5 K indicates a strong absorption feature close
to 10 cm~^ in the superconducting state with a reference temperature of 4.2 K.
By means of Kramers-Kronig analysis, the absolute reflectance was used to calculate the optical
conductivity and dielectric function. The real part of optical conductivity shows five distinct active
phonon modes at 44, 200, 300, 375, and 575 cm~' at all temperatures including a Drude-like
behavior at low frequencies. The imaginary part of the calculated dielectric function indicates a
mode softening of the mode 44 cm~' below Tc.||en_US