Effect of glycine doping on structure, linear optical properties, and ionic conductivity of ammonium dihydrogen phosphate crystals

Pure and glycine-doped ammonium dihydrogen phosphate (ADP) crystals have been grown using the slow solvent evaporation technique at room temperature. An investigation has been conducted to examine the effect of glycine doping on structural, vibrational, and optical properties and conductivity mechanism of pure ADP crystals. The analysis of powder XRD profile has suggested tetragonal structure symmetry with improved crystallite size and reduced lattice strain by glycine doping. The Raman spectrum study has indicated the presence of the characteristic vibrations of PO₄^3- and NH₄⁺ groups at around 925 cm^-1 and 1660 cm^-1, respectively. The influence of glycine doping on the linear properties of the pure ADP crystal has been determined based on the optical transmittance spectra. The direct optical bandgap increases by glycine doping; it is found to be 6.18 for pure ADP crystal and increases up to 6.25 for glycine-doped ADP crystals. The linear refractive index, optical density, extinction coefficient, optical conductivity, electric susceptibility, optical dielectric constant and loss, inter-band transition strength, volume, and surface energy loss factor have been found to be influenced by glycine doping. The optical study is further extended using the Wemple–DiDomenico single-oscillator model. The frequency-dependent ionic conductivity has been studied and obeys Jonscher’s power law. The modulus study shows that the conductivity relaxation is of non-Debye type. The exponent parameter for the pure ADP crystal is 0.620 and increases up to 0.691 for glycine-doped ADP crystals.