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

Abstract

Resistance degradation due to interstitial hydrogen in photorefractive potassium lithium tantalate niobate single crystals J. Appl. Phys. 96, 6405 (2004); 10.1063/1.1810195 An approach to the defect structure analysis of lithium niobate single crystalsThe defect structures of impurity-doped congruent lithium niobates (c-LN) were determined for impurities with various valences, including divalent, trivalent, and tetravalent impurities, in a concentration range where antisite niobium (Nb Li ) exists. On the basis of the "Li site vacancy model," six kinds of defect structures in impurity-doped c-LN are possible. Using thermodynamic constraints, these can be narrowed down to two kinds. The first structure is that in which impurities, vacancies and Nb exist as defects in the Li site and no defects exist in the Nb site (structure A), described as f½Li Li 1À5xÀjy ½Nb Li x ½M Li y ½V Li 4xþðjÀ1Þy g½Nb Nb ½O O 3 (V: vacancy, M: impurity, j: valence of impurity, x, y: compositional variable (6 ¼0),Li 4xþy g½Nb  Nb ½O  O 3 is an example by the Kr€ oger-Vink notation for divalent M. In the second structure, vacancies and Nb exist as defects in the Li site and impurities exist as defects in the Nb site (structure B), described as f½Li Li 1À5xÀðjÀ5Þy ½Nb Li x ½V Li 4xþðjÀ5Þy gf½Nb Nb 1Ày ½M Nb y g½O O 3 . f½Li  Li 1À5xþy ½Nb •••• Li x ½V 0 Li 4xÀy gf½Nb  Nb 1Ày ½M 0 Nb y g½O  O 3 is an example for tetravalent M. Since the relationship between impurity concentration and lattice constants for structures A and B differs, the defect structures can be differentiated by analyzing lattice constant variations as a function of impurity concentration. The results show that the defect structure of divalent and trivalent impurity-doped c-LN is structure A and that of tetravalent impurity-doped c-LN is structure B. The Nb Li concentration increased with increasing tetravalent impurity concentration. In contrast, the Nb Li concentration decreased with increasing divalent and trivalent impurities, leading to suppression of optical damage. The valence of an impurity determines whether the impurity is located in the Li site or Nb site in c-LN, consequently determining whether Nb Li decreases or increases when the population of the impurity changes. V C 2015 AIP Publishing LLC. [http://dx.

Lattice Parameters of Optical Damage Resistant In-Doped LiNbO3 Crystals

“…Namely, in LiNbO 3 -Zn a decrease of c [19] and a plateau in the lattice-cell volume (Figure 1b) below 3% Zn is accounted for by the removal of Nb-antisites, whereas an increase of c and V at [Zn] >3% is related to increasing number of Li-vacancies. According to the calculations of [29], Nb-antisites disappear at divalent-impurity concentrations of 3%, which is in excellent agreement with the data for LiNbO 3 -Zn. For the tetravalent ODRI, the calculations of [29] predict the removal of Nb-antistes at concentrations of about 1.6 mol %.…”

“…According to the calculations of [29], Nb-antisites disappear at divalent-impurity concentrations of 3%, which is in excellent agreement with the data for LiNbO 3 -Zn. For the tetravalent ODRI, the calculations of [29] predict the removal of Nb-antistes at concentrations of about 1.6 mol %. A drop of c-parameter in LiNbO 3 -Zr is observed at [ZrO 2 ] of 1.5 and 2.0 mol % [23], which permits us to attribute this anomaly to the removal of Nb-anisites again.…”

“…Analogously, it would be reasonable to assign a decrease of c-parameter in LiNbO 3 -In at [In] ≤0.5 at % (Figure 1a) to the disappearance of Nb Li . However, this conclusion disagrees with the calculations of [29], according to which Nb-antisites disappear at the trivalent ODRI concentration of 2.1%. Moreover, based on the IR measurements in LiNbO 3 -Sc, the authors of [31] arrived at the conclusion that Nb-antisites are absent at Sc 2 O 3 > 2 mol %, which agrees with the estimates of [29].…”

“…in [1]) is still under debate. Recently, a general consideration of different impurity incorporation into the LiNbO 3 lattice was presented in [29]. An a priori confidence about ODRI incorporation into the Li-sites, at least at low doping was confirmed by numerous experiments.…”

“…So, the anomaly of c-parameter at In-concentrations ≤0.5 at % is related to the removal of Nb-antisites. We now speculate about the reason of why the concentration range of the structure anomaly in LiNbO 3 -In does not conform to the consideration of [29]. The calculations of [30] have shown that for trivalent ions the incorporation into two-cation (Li-and Nb-) sites in LiNbO 3 is energetically favorable since it provides the charge self-compensation; in the case of In-doping it would be presented as In 2• Li -In 2 Nb .…”