Dielectric relaxation, protonic defect, conductivity mechanisms, complex impedance and modulus spectroscopic studies of pure and L-threonine-doped ammonium dihydrogen phosphate

Ammonium dihydrogen phosphate (ADP) has a wide range of applications in integrated and nonlinear optics. The dopant-like L-threonine has hydrogen-bonded side chain that causes defects in ADP. The pure and L-threonine-doped ADP crystals are grown using slow evaporation technique. The powder XRD patterns show the single-phase nature of pure and doped ADP. The dielectric constant and dielectric loss have shown the usual behaviour with respect to frequency and temperature. The protonic conduction is prevailing for electric transport, and from Jonscher’s plot, the correlation barrier hopping (CBH) and non-overlapping small polaron tunnelling (NSPT) conduction mechanism is confirmed. The Nyquist plot and modulus spectra show the presence of grain and grain boundary. The stretch exponent exhibits non-Debye-type relaxation. The activation energy of relaxation time for all samples is calculated. The modulus master curve and variation of Z″ and M″ versus angular frequency confirmed the proposed conduction. The nonlinear optical counterpart is in accordance with dielectric results.