Nonstoichiometry and electrocoloration due to injection of Li+ and O2− ions into lithium niobate crystals

Abstract

The high oxygen and lithium ion conductivity in LiNbO3 was investigated and interpreted in terms of lithium and oxygen vacancies being intrinsically present in congruently grown single crystals. As a result of this, it was found that the stoichiometry of lithium niobate crystals may be changed with respect to lithium and oxygen. The optical and electrical properties of electrically colored LiNbO3 crystals were studied and it was shown that the absorption spectra of thermally reduced and electrocolored samples are identical. Therefore, the origin of the absorption processes is considered to be the same in both cases. The formation of regions with different stoichiometry due to the injection of additional lithium or oxygen into the LiNbO3 crystals was also observed and investigated. The motion of these stoichiometric domains through a LiNbO3 crystal from one electrode to the other was studied and described in terms of electrodiffusion of the ions and electrons. A model is proposed which considers the injection of oxygen and lithium vacancies for the generation of concentration profiles in the originally homogeneous material. The numerical calculation of the concentration profiles shows good agreement with the experimental results.

Investigation of defect structure of impurity-doped lithium niobate by combining thermodynamic constraints with lattice constant variations

“…Several defect models of congruent LN (c-LN) have been proposed based on experimental evidence and simulation results, [3][4][5][6][7][8][9][10] and the "Li site vacancy model" is commonly accepted as valid. In the "Li site vacancy model," excess Nb exists as antisite niobium in the Li site (Nb Li ).…”

Electrical Properties of LiTaO3Single Crystals at 290–450 K

“…Let us discuss the possible reasons of these discrepancies. First of all, the W ac2 value for reduced LT sample is indicative of the polaronic conductivity at low temperatures [13], but the highest value W ac1 is close to the probable activation energy of oxygen vacancies V O diffusion [12]. On the other hand, the highest value W ac1 for as-grown crystal is typical for hydrogen conductivity in LT and LN crystals, while W ac2 value is indicative of the hopping electronic conductivity [10,14].…”

“…It should be noted that for the V O diffusion in the isomorphic LiNbO 3 crystals W ac is equal approximately to 1.4 eV [12,17]. Therefore, in a process of s(G) simulations we take into consideration any activation energies of V O diffusion in the range (1.40-1.55) eV.…”

Исследование стабильности электрических свойств восстановленных кристаллов LiNbO-=SUB=-3-=/SUB=-

“…Исходя из изложенного, можно сделать вывод о том, что диффузия кислорода в восстановленных кристаллах НЛ в области температур, близких к комнатной, гораздо более интенсивна, чем можно было бы предположить, основываясь на известных данных [14][15][16][17]. Исследова-нию процессов диффузии кислорода в восстановленных кристаллах НЛ при низких температурах будет посвя-щена отдельная работа.…”