Phase transitions in the Na3PO4-BiPO4 system |
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| Authors: | M Diouri M Drache F Abraham J P Wignacourt |
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| Institution: | Laboratoire de Cristallochimie et Physicochimie du Solide, UA CNRS 452, Ecole Nationale Supérieure de Chimie de Lille B.P. 108 , 59652 , Villeneuve D'Ascq, Cédex , France |
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| Abstract: | Abstract The Na3PO4-BiPO4 system has been investigated by X-ray diffraction and D.T.A. It features two definite compounds: Na3Bi(PO4)2 and Na3Bi5(PO4)6, the first one being polymorphic. It crystallizes in two orthorhombic and two hexagonal forms below melting at 1025°C. The H.T. phase has the glaserite structure, and the other ones are related. Na3Bi5(PO4)6 is stable only at 680 ? t ? 820°C, but can easily be quenched. It has a non-centrosymmetric cubic structure (S.H.G.) of the eulytite type, and so potential piezoelectric applications can be expected. Na3PO4 and Na3Bi(PO4)2 display two extensive ranges of solid solutions with the replacement mechanism 3Na+ → Bi3+ in the formula Na3-3x Bi x PO4, respectively with 0 ? x ? 0.29 and 0.5 ? x ? 0.62 over 950°C. |
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| Keywords: | Phase diagram polymorphism phase transition orthophosphate piezoelectricity |
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