$\mathrm{K}{\mathrm{H}}_2\mathrm{P}{\mathrm{O}}_4$ (KDP) crystals doped with Mn ions were studied by an x-ray multiple diffraction technique using synchrotron radiation at room temperature. Asymmetric peaks were observed for both undoped and doped crystals, a characteristic of perfect crystals. X-ray powder diffraction at room temperature and analysis by Rietveld refinement were also performed, showing that doped KDP has the same tetragonal structure as undoped KDP, but with contraction of the lattice parameter for [100], [010], and [001] directions. The polarized Raman spectra of KDP and KDP:Mn were obtained for temperatures in the range $10–300\mathrm{K}$. Some of the features observed in the spectra were interpreted as consequences of phase transitions. Although group theory analysis shows that both doped and undoped crystals have the same symmetry at room temperature, at low temperature they have different symmetries: a previously reported phase transition for KDP at $60\mathrm{K}$ was not observed for KDP:Mn.

• Received 28 January 2005

DOI:https://doi.org/10.1103/PhysRevB.72.014121