Abstract
Existent methods for determining the composition of lithium niobate single crystals are mainly based on their variations due to changes in their electronic structure, which accounts for the fact that most of these methods rely on experimental techniques using light as the probe. Nevertheless, these methods used for single crystals fail in accurately predicting the chemical composition of lithium niobate powders due to strong scattering effects and randomness. In this work, an innovative method for determining the chemical composition of lithium niobate powders, based mainly on the probing of secondary thermodynamic phases by X-ray diffraction analysis and structure refinement, is employed. Its validation is supported by the characterization of several samples synthesized by the standard and inexpensive method of mechanosynthesis. Furthermore, new linear equations are proposed to accurately describe and determine the chemical composition of this type of powdered material. The composition can now be determined by using any of four standard characterization techniques: X-Ray Diffraction (XRD), Raman Spectroscopy (RS), UV-vis Diffuse Reflectance (DR), and Differential Thermal Analysis (DTA). In the case of the existence of a previous equivalent description for single crystals, a brief analysis of the literature is made.
Highlights
Nowadays, more than 50 years after Ballman managed to grow large lithium niobate (LiNbO3 ; LN) crystals with the Czochralski method [1], synthesizing stoichiometric LN single crystals is still a state-of-the-art matter: The reason behind this is the fact that a Z-cut of a stoichiometric grown crystal costs around 12 times more than one possessing a congruent chemical composition [2]
Cementation materials based on LN have been proposed as a way to improve the air quality of the environment by Artificial Photosynthesis; this is considered important for the reduction of global warming [9]
Regarding LN powders (LNPws), we emphasize that would they be easier than single crystals to implement into cemented materials, but they would probably enhance the intrinsic surface effects, which are the basis for an improvement of the lifetime of the carriers involved in Artificial Photosynthesis [10]
Summary
More than 50 years after Ballman managed to grow large lithium niobate (LiNbO3 ; LN) crystals with the Czochralski method [1], synthesizing stoichiometric LN single crystals is still a state-of-the-art matter: The reason behind this is the fact that a Z-cut of a stoichiometric grown crystal costs around 12 times more than one possessing a congruent chemical composition [2] Compared to this version of the material, while comprehensively studied [3] and well exploited technologically [4,5,6], powders are tacitly considered easier and far less expensive to synthesize. This could soon translate into major technical benefits given that neither a critical adjustment of the orientation or temperature in the material (phase matching condition) nor the accurate engineering of a microstructure (quasi-phase matching condition) are substantially needed when the SHG from disordered materials—such as LNPws—are exploited [14]
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