Whitlockite solid solutions in the Ca3(VO4)2-K3VO4-NdVO4 system |
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Authors: | I. A. Leonidov L. L. Surat O. N. Leonidova |
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Affiliation: | 1.Institute of Solid-State Chemistry, Ural Branch,Russian Academy of Sciences,Yekaterinburg,Russia |
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Abstract: | Phase equilibria in the Ca3(VO4)2-K3VO4-NdVO4 system have been studied. An extensive calcium orthovanadate-based solid solution was found to form with the boundary compositions as follows: Ca3(VO4)2-Ca9Nd(VO4)7-Ca9.33K2.33(VO4)7-Ca7.88K2.63Nd0.87(VO4)7. The unit cell parameters of the whit-lockite vanadates synthesized increase as the potassium and neodymium contents increase. Phase transitions from the low-temperature β phase to the β′ centrosymmetrical structure in Ca9.33 − 5z K2.33 + z Nd3z (VO4)7 vanadates have been studied dilatometrically. The increase in the β ai β′ transition temperature caused by potassium is interpreted as arising from the filling in of vacant cation positions M(4) and M(6). |
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