The cationic and oxygen nonstoichiometry of sodium-gadolinium molybdates

The content of all matrix elements, including oxygen, was determined by X-ray spectral microanalysis in series of single crystals of sodium-gadolinium molybdates (NGM) grown from melt by Czochralski technique. All grown NGM crystals, including those grown from stoichiometric charge, are non-stoichiometric and contain a molybdenum deficiency of about 3% in average. The NGM congruently melting composition has been determined. For crystals grown from melt of equimolar (stoichiometric) composition, the content of cationic vacancies in the (Gd + Na) sublattice is close to zero, while the composition of crystal differs from the initial melt. As the Gd excess increases, the content of cationic vacancies in the (Gd + Na) sublattice increases up to 10%. It has been found that cation-deficient NGM crystals are also anion-deficient. The concentration of oxygen vacancies varies from 0.5% to 5% of the amount of anion sites. Possible mechanisms responsible for the formation of cationic and anionic vacancies in NGM crystals are discussed. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study reveals that grown NGM crystals are non-stoichiometric with molybdenum deficiency, and the content of cationic vacancies increases up to 10% with Gd excess. Oxygen vacancies in the crystals vary from 0.5% to 5% of anion sites, indicating possible mechanisms for the formation of cationic and anionic vacancies in NGM crystals.