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New compounds NaBaM(BO₃)₂ (M = Sc, Y, Yb, Dy)

Svetlyakova T.

V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia

svetlyakovatn@gmail.com

Simple and complex rare earth borate compounds are widely used as laser matrices or non-linear optical materials. The complex rare earth borates with alkali metals, for instance, LnNa₃(BO₃)₂ (Ln = Y, La, Nd, Gd) [1; 2] and Ln₂Ba₃(BO₃)₄ (Ln = La, Pr, Gd) [3] are of great interest due to luminescent properties and low concentration quenching of the rare earth ion [4].

In our previous study of the MBO₃-BaB₂O₄-Na₂B₂O₄ (M = Sc, Y) system a chemical reaction between the initial components was found. As a result a new compounds BaNaSc(BO₃)₂ and BaNaY(BO₃)₂ were discovered [5]. This suggests the presence of similar compounds with other rare earth elements.

Search of new NaBaLn(BO₃)₂ compounds (Ln = La-Lu) was done using two-step solid phase synthesis and spontaneous crystallization [6].

P owder samples of BaNaLn(BO₃)₂ were prepared by two-step solid phase synthesis. At the first stage the mixture was heated at 800 ^oC for 16 hours to remove CO₂ and H₂O. The duration of the process was controlled on the basis of the

Fig. X-ray spectra of the crystal samples of: NaBaDy(BO₃)₂ (a); NaBaYb(BO₃)₂ (b); NaBaSc(BO₃)₂ (c), NaBaY(BO₃)₂ (d).

loss of initial charge weight. The temperature of the second stage was found with a stepwise 50–70 ^оС increase of the temperature. After each stage of the heat treatments the X-ray powder diffraction analysis was carried out. After reaching the complete reaction between the components the annealing process was stopped. A criterion for the completion of the process was the absence of signals of admixture phases in the X-ray diffraction patterns of the synthesized powders. The heat treatment at both stages was alternated with careful grinding of intermediate reaction products.

Among the whole range of rare earth elements the X-ray powder diffraction pattern of compounds with ions Yb³⁺ and Dy³⁺ contained no lines of famous borates with these elements, and we failed to identify the existing set of peaks.

Search of the solvents for crystal growth was held on the base of experiments with NaBaSc(BO₃)₂ and NaBaY(BO₃)₂. The solvents under study are: BaO-B2O3-Na2O (eutectic Е₁: 0.56 BaB₂O₄ - 0.44 NaBO₂, melt temperature 826 ^оС; eutectic Е₂: 0.56 NaBO₂-0.44 BaNaBO₃, 830 ^оС); NaBO₂ (966 ^оС); 0.39 BaB₂O₄-0.61 NaF (754 ^оС). The major parameters for choosing the best solvent was crystal yield coefficient and overall solubility of compound in the system.

The highest yield coefficient of NaBaSc(BO₃)₂ compound was found for 0.56 BaB₂O₄-0.44 NaBO₂ solvent and equals 2.644. Nevertheless it is difficult to grow NaBaY(BO₃)₂ crystal in this system because the solubility is less than 5 weight %. Next experiments showed that the most effective solution for crystal growth for both compounds is 0.39 BaB₂O4-0.61 NaF system. The yield coefficients are high and the crystallization temperatures of the compounds are rather low. This solution was used for crystal grow of new compounds with ions Yb³⁺ and Dy³⁺.

X-ray spectra of the sintered powders of new compounds are in full agreement with that of the single crystals. Fig. (a, b, c, d) demonstrates identical peak locations on X-ray spectra of NaBaSc(BO₃)₂, NaBaY(BO₃)₂ and new compounds with Yb³⁺ and Dy³⁺ ions. Thus it may be conclude the compositions of new compounds are NaBaYb(BO₃)₂ and NaBaDy(BO₃)₂, respectively.

All compounds crystallized in one structural type ( .space group) and belong to one family of complex island layered ortoborates [7]. For all studied orthoborates structural characteristics were calculated.

References.

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3. Palkina K.K., Kuznetsov V.G., Dzhurinskii B.F., Moruga L.G. (1972) Russ. Inorg. Chem. 1972. V. 17. 341pp.

4. Blasse G., Bril A. (1967) J. Inorganic. Nucl. Chem. 29. 266pp.

5. Svetlyakova T.N., Kononova N.G., Kokh A.E., Kokh K.A., Pal’chik N.A. (2011) Russ. J. Inorg. Chem. 56. No 1. 117-121pp.

6. Svetlyakova T., Kokh A., Kononova N. (2011) The materials of XVII International congress “Crystal Chemistry, XRD and Spectroscopy”. St.Petersburg, 151-152pp.

7. Seryotkin Y., Bakakin V., Kokh A., Kononova G., Svetlyakova T., Kokh K., Drebushchak T. (2010) Journal of Solid State Chem. 183. № 5. 1200-1204pp.