Dielectric relaxation in single crystal NH4H2PO4 in the high-temperature regime

The dispersion curves of the dielectric response in single crystal NH4H2PO4 were obtained in the radio frequency range and below the high-temperature transition at Tp−160 °C. The results reveal dielectric relaxation at low frequency, which is about 105 Hz at 70 °C, and it shifts to higher frequencies (∼3×106 Hz) as the temperature increases. The relaxation frequency was determined from the peak obtained in the imaginary part of the permittivity as well as from the derivative of the real part of the permittivity. The activation energy Ea=0.55 eV, obtained from the relaxation frequency is very close to that derived from the dc conductivity. We suggest that this dielectric relaxation could be due to the proton jump and phosphate reorientation that cause distortion and change the local lattice polarizability inducing dipoles like H 2 PO 4 − .