Raman studies on potassium-ammonium dihydrogen phosphate systems [(KDP)1−x(ADP)x]

We have studied pressed-pellet samples of potassium-ammonium dihydrogen phosphate [${\left(\mathrm{KDP}\right)}_{1-x}{\left(\mathrm{ADP}\right)}_x$] by Raman scattering for $x=0\mathrm{}$, $x=0.5\mathrm{}$, and $x=1\mathrm{}$ at room temperature and liquid-nitrogen temperature. The liquid-nitrogen-temperature spectra of pure KDP and ADP pellets showed the characteristics of their ferroelectric and antiferroelectric phases, respectively. However, the low-temperature spectra of the ${\mathrm{}\left(\mathrm{KDP}\right)\mathrm{}}_{0.5}$ ${\mathrm{}\left(\mathrm{ADP}\right)\mathrm{}}_{0.5}$ pellets showed features that were characteristic of a structural glass formation as found previously in single-crystal samples of rubidium-ammonium dihydrogen phosphate [${\left(\mathrm{RDP}\right)}_{1-x}{\left(\mathrm{ADP}\right)}_x$], such as the persistence of the continuum soft-mode structure and local freezing of N${\mathrm{H}}_4^{+}$ units.