UNSPECIFIED. (1994) A COMPARATIVE STRUCTURAL STUDY OF A FLUX-GROWN CRYSTAL OF K0.86RB0.14TIOPO4 AND AN ION-EXCHANGED CRYSTAL OF K0.84RB0.16TIOPO4. ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 50 (Part 5). pp. 538-543. ISSN 0108-7681

Abstract

The crystal structures of a flux-grown crystal, K0.86Rb0.14TiOPO4, and an Rb/Ba ion-exchanged KTiOPO4 crystal, K0.84Rb0.16TiOPO4, are refined and compared. Both crystals are isostructural with potassium titanyl phosphate, KTiOPO4. In both crystals, Rb substitutes for K only on the K(2) site with the crystallographically distinct K(1) site being solely occupied by K. However, in the ion-exchanged crystal, a residual electron density (2.6 e Angstrom(-3)) is found on a site that is normally a void in the KTiOPO4 structure and that has been suggested as an essential site in the process of domain inversion by ion exchange in KTiOPO4. This residual density was refined as part-occupancy of the site by either Rb or Ba, and this gave occupancies of 0.038 (3) or 0.027 (2), respectively. The results of these structural analyses are discussed in the context of structural models for domain inversion by ion exchange. Crystal data for potassium rubidium titanyl phosphates at room temperature: (1) K0.86Rb0.14TiOPO4, M(r) = 204.44, orthorhombic, Pna2(1), a = 12.8500 (8), b = 6.4136 (3), c = 10.5912 (7) Angstrom, Z = 8, R = 0.021 for 2584 reflections with I > 3 sigma(I). (2) K0.84Rb0.16TiOPO4, M(r) = 205.34, orthorhombic, Pna2(1), a = 12.858 (3), b = 6.4125 (7), c = 10.592 (1) Angstrom, Z = 8, R = 0.032 for 1576 unique reflections with I > 1.2 sigma(I).

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