Room-temperature A₁(TO) and OH^- absorption spectra of Zn-doped lithium niobate crystals

A₁(TO) phonons and OH^- absorption spectra of Zn-doped lithium niobate crystals were measured by Raman and infrared spectroscopies at room temperature. Zn doping concentrations are from 0 to 8.1 mol.%. The characterizations of A₁(TO)-phonon lineshapes and OH^- absorption bands as a function of Zn concentration were carried out. The results revealed from Raman and OH^- absorption analyses show consistency in the changes of phonon lineshapes and OH^- absorption bands. The spectra revealed three different stages of Zn substitution. Based on the Li-vacancy model, the proposed Zn substitution mechanism is: (i) below 5.3 mol.%, Zn atoms replace Li atoms and the total number of Li vacancies is reduced; (ii) from 5.3 to 7.5 mol.% doping, Zn atoms still replace Li atoms but the number of vacancies increases; (iii) above 7.5 mol.% doping, Zn atoms start to replace Nb atoms.