Xiao Xuefeng, Xu Qingyan, Liang Shuaijie, Zhang Huan, Ma Lingling, Hai Lian, Zhang Xuefeng
College of Electric and Information Engineering, North Minzu University Yinchuan China
Key Laboratory of Physics and Photoelectric Information Functional Materials Sciences and Technology, North Minzu University Yinchuan China.
RSC Adv. 2022 Jun 30;12(30):19091-19100. doi: 10.1039/d2ra02775e. eCollection 2022 Jun 29.
A vapour transfer equilibrium (VTE) method has been used to prepare near-stoichiometric lithium tantalate (NSLT) crystals with different Li contents. The NSLT crystals were tested and analyzed by differential thermal analysis (DTA) and X-ray photoelectron spectroscopy (XPS) to investigate the effect of Li content on the Curie temperature and internal defects of NSLT crystals. This study found that when the Li content increased in the NSLT wafer, the binding energy corresponding to the peak of the Ta electron layer in the XPS spectrum first decreased and then increased, indicating that the proportion of Ta valence states was different in wafers with different Li contents. From XPS energy spectrum analysis, it can be seen that the lithium tantalate crystal contains Ta, Ta, Ta and lower-valence Ta. As the Li content increases in the NSLT wafer, Ta disappears and the proportion of Ta decreases initially, follows by a later increase and then subsequent further decrease. However, the change in proportion of Ta and lower-price Ta is completely opposite to that of Ta, showing a trend of first rising, then falling and then finally rising again. Moreover, when the Li content is 49.751% in the NSLT wafer, the proportion of Ta reaches a maximum, showing that at this Li concentration the NSLT crystal has a more perfect lattice structure. In this study, we propose a mixed defect model in which polarons coexist with Li vacancies and Ta inversion, explaining the change in Ta valence state in lithium tantalate crystals. This model is more in line with the observed results in this work. The new hybrid defect model and the variation law of Ta valence state with Li concentration proposed in this paper provide a new direction and experimental proof for the defect study of NSLT crystals, and also provide a theoretical basis to explore the Li content at the best physical properties of NSLT crystals.
采用气相转移平衡（VTE）法制备了不同锂含量的近化学计量比钽酸锂（NSLT）晶体。通过差示热分析（DTA）和X射线光电子能谱（XPS）对NSLT晶体进行测试和分析，以研究锂含量对NSLT晶体居里温度和内部缺陷的影响。本研究发现，当NSLT晶片的锂含量增加时，XPS光谱中Ta电子层峰对应的结合能先降低后升高，这表明不同锂含量的晶片中Ta价态的比例不同。从XPS能谱分析可以看出，钽酸锂晶体含有Ta、Ta、Ta和低价Ta。随着NSLT晶片中锂含量的增加，Ta消失，Ta的比例最初降低，随后增加，然后进一步降低。然而，Ta和低价Ta比例的变化与Ta完全相反，呈现出先上升、再下降、最后又上升的趋势。此外，当NSLT晶片中锂含量为49.751%时，Ta的比例达到最大值，这表明在该锂浓度下NSLT晶体具有更完美的晶格结构。在本研究中，我们提出了一种混合缺陷模型，其中极化子与锂空位和Ta反位共存，解释了钽酸锂晶体中Ta价态的变化。该模型更符合本工作中观察到的结果。本文提出的新的混合缺陷模型以及Ta价态随锂浓度的变化规律为NSLT晶体的缺陷研究提供了新的方向和实验依据，也为探索NSLT晶体最佳物理性能时的锂含量提供了理论基础。
