IMF2017

Physical and chemical properties of the LiNbO₃ can be modified during redox process and proton exchange reaction (PE). As a result of this treatment the significant lithium deficiency and concentration of defects in the surface of reduced lithium niobate crystal was observed. In our study we have analyzed an influence of reduction (in situ, under UHV, temperature: 20 - 800 °C) and oxidation (in situ, pure oxygen pressure (99.9999%): 6.4 x 10^-7-100 mbar, T = const.) processes on dielectric properties of the crystal. Dielectric spectroscopy investigation was obtained in situ at the frequency range from 1MHz to 1mHz for two set of samples: congruent and congruent with modified surface using proton exchange reaction (PE). The similar investigation of dielectric properties was obtained for sample modified with PE. Analysis of Cole-Cole plots showed that an equivalent circuit for reduction and oxidation reaction could be described as a typical Maxwell–Wagner capacitor. One of the Maxwell–Wagner inset was assigned to interior part of sample, second one to the crystal surface. Our study of temperature dependence vs Z' and Z" with respect to the thermal and chemical treatment showed various characters of activation energy for both contributions. Brillouin scattering study was used to enhance dielectric spectroscopy study. The T_c ~ 1120 °C value, determined in terms of the ex situ Brillouin scattering, was similar for all samples. However, unexpected anomaly in the Brillouin frequency shift was observed for proton exchange samples in vicinity of T_c for the longitudinal acoustic mode in contrast to referenced sample without anomaly.