Models with two lithium vacancies explain angular dependencies of EPR spectra for Me 3+ ions substituting for Li + like Cr, Er, Fe, Gd, Nd, and Yb. Self-compensation of excessive charges through equalization of concentrations of Me 3+(Li +) and Me 3+(Nb 5+) and appearance of interstitial Li + in the structural vacancy near Me 3+(Nb 5+) take place in stoichiometric LN/LT due to lack of intrinsic defects. Point intrinsic and extrinsic defects, especially paramagnetic ions of transition metals and rare-earth elements, belong to the most important defects in lithium niobate (LN, LiNbO 3) and tantalate (LT, LiTaO 3), because of their essential influence on properties of this material, such as domain structure, electro-optical coefficients, light absorption, refractive indices, birth and evolution of wave-front dislocations ( and references there), and their consequences for present and potential applications. A lot of effort was spent to establish a correlation between the observable data and the crystal composition, and to develop experimentally supported models of the defects: ion charges, identities, and position of the ions in the lattice, their nearest surroundings, ways of charge compensation and recharge mechanisms. Discussions about structures of intrinsic and extrinsic defects in LN/LT have lasted for decades.
With time, the proposed structures were evolved and detailed. #Draw fe crystal in crystalmaker softwareįor instance, after a supposition that effective net charges are about 2.0+, or 1.59+ for Nb and 1.21+ for Ta, it was natural to assume that divalent and trivalent impurities should preferably substitute for Nb, but not for Li.#Draw fe crystal in crystalmaker mac os x.#Draw fe crystal in crystalmaker for free.
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