  The detailed temperature dependence of the infrared-active mode in
Fe$_{1.03}$Te ($T_N\simeq 68$ K) and Fe$_{1.13}$Te ($T_N\simeq 56$ K) has been
examined, and the position, width, strength, and asymmetry parameter determined
using an asymmetric Fano profile superimposed on an electronic background. In
both materials the frequency of the mode increases as the temperature is
reduced; however, there is also a slight asymmetry in the line shape,
indicating that the mode is coupled to either spin or charge excitations. Below
$T_N$ there is an anomalous decrease in frequency and the mode shows little
temperature dependence, at the same time becoming more symmetric, suggesting a
reduction in spin- or electron-phonon coupling. The frequency of the
infrared-active mode and the magnitude of the shift below $T_N$ are predicted
reasonably well by first-principles calculations; however, the predicted
splitting of the mode is not observed. In superconducting
FeTe$_{0.55}$Se$_{0.45}$ ($T_c\simeq 14$ K) the infrared-active $E_u$ mode
displays asymmetric line shape at all temperatures, which is most pronounced
between 100 - 200 K, indicating the presence of either spin- or electron-phonon
coupling, which may be a necessary prerequisite for superconductivity in this
class of materials.
