Phase transitions of $(RDP)_{1-x}(ADP)_x$ mixed crystal for x=0.52 was investigated by Raman and dielectric measurements in the presence of external bias electric field. In the dielectric constant measurement the dc electric field was observed to lower the magnitude of dielectric constant. But it did not change the glass transition temperature or the onset of freezing temperature. In the limit of our resolution We could not find the x-z anisotropy in electric susceptibility. In Raman scattering spectra the electric effect was not observed up to the highest possible applied field of 10.8 kV/cm. The rwsidual strains associated with the lattice mismatch may have already created the site symmetry changes expected from the external applied field.
