Evaluation of similarities and differences of LiTaO₃ and LiNbO₃ based on high-T-conductivity, nonlinear optical fs-spectroscopy and ab initio modeling of polaronic structures

Abstract

Different aspects of ferroelectric LiTaO3 (LT) such as polaronic defects, optical response and electrical conductivity are investigated by the most recent theoretical and experimental approaches. Comparing the results with the state-of-the-art knowledge of the widely studied LiNbO3 (LN), we evaluate the general assumption that there is little difference between the aforementioned properties of LT and LN. First-principles calculations reveal the existence of point defects in LT qualitatively compatible with the polaronic picture established in LN. Though, peculiar differences with respect to the individual binding energies and polaronic deformation can be revealed. Accordingly, (sub-)picosecond transient absorption measurements show pronounced differences in the kinetics in the sub-ps time domain of small polaron formation and, even more pronounced, in the long-term evolution identified with small polaron hopping. In contrast, (sub-)ps transient luminescence, attributed to the relaxation of self-trapped excitons in LN, shows very similar kinetics. Electrical conductivity measurements are performed in air as function of temperature. Up to about 600 °C they demonstrate similar temperature dependence for the two materials, from which rather comparable activation energies can be extracted. However, in the high-temperature range from about 600 °C to 920 °C both materials show noticeable differences. The results suggest that the fundamental microscopic understanding of LN can be in part transferred to LT. However, due to differences in structure, energetic landscape and temperature behavior, discrepancies between the two materials bear a striking potential for novel applications, even at high temperatures.

Nonlinear optical response of ferroelectric oxides: first-principles calculations within the time-domain and the frequency-domain

“…2. It features a very flat dispersion of both valence and conduction states, which is characteristic of the material [32,43,44]. The indirect (direct) fundamental electronic bandgap amounts to 3.52 eV (3.42 eV) which also is in agreement with earlier calculations [32,39].…”

Correlation of Electrical Properties and Acoustic Loss in Single Crystalline Lithium Niobate-Tantalate Solid Solutions at Elevated Temperatures

“…Here, compensation of Nb antisites occurs by Li-vacancies. In an analogy to the defect model for nonstoichiometric LiNbO 3 , the congruent LiTaO 3 single crystals also contain a large amount of the tantalum antisites and cation vacancies [20][21][22]. The defect models for LNT are still to be established.…”

The influence of sodium deficiency and titanium doping concentration on conduction properties in NaTaO3−δ

“…With better control of Na deficiency, adjustment of Ti‐doping concentration, and improved sintering of the samples, the total conductivity of Ti‐doped NaTaO 3 was significantly increased compared to previous work on the same material 20 . The 3% Ti‐doped NaTaO 3 sample has the highest total conductivity at intermediate temperatures, so its total conductivity is plotted in Figure 13 in comparison with other discussed I–V perovskites and BZY20 6,13–17,26 . From Figure 13, one can see that the conductivity of Ti‐doped NaTaO 3 is one of the highest among all discussed I–V perovskites, which is quite close to that of 15% Ti‐doped NaNbO 3 , and about 10 times lower than that of 50% Al‐doped KNbO 3 at 600°C.…”