  Manganites with double perovskite structure are being attractive because of
their interesting magnetoelectric and dielectric responses. Particularly,
colossal dielectric constant (CDC) behavior has been observed in
La$_2$CoMnO$_6$ (LCMO), at radio frequencies and room temperature. In this
paper, we employed infrared-reflectivity spectroscopy onto a LCMO ceramic
obtained through a modified Pechini's method to determine the phonon
contribution to the intrinsic dielectric response of the system and to
investigate the CDC origin. The analysis of the main polar modes and of the
obtained phonon parameters show that CDC effect of LCMO is of pure extrinsic
origin. In addition, we have estimated the dielectric constant and quality
factor of the material in microwave region, $e'_s \sim 16$ and $Q_u \times f
\sim 124$ THz, which shows that LCMO is appropriate for applications into
microwave devices and circuitry.
