Preparation of Ti-less aliovalent substituted isomorphs of KTiOPO 4
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Preparation of Ti-less aliovalent substituted isomorphs of KTiOPO4 Valery I. Chania) Center for Interdisciplinary Research, Tohoku University, Aramaki aza Aoba, Aoba-ku, Sendai, 980-8578, Japan
Kiyoshi Shimamura, Shinji Endo, and Tsuguo Fukuda Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan (Received 14 October 1998; accepted 26 February 1999)
KTiOPO4 (KTP) phase formation in stoichiometric mixtures corresponding to chemical formulas of hA1 j fB51 1/2 C31 1/2 gOsD51 dO4 (A K1 ; B Nb51 and Ta51 ; C Al31 , Cr31 , Ga31 , Fe31 , and In31 ; and D P51 and As51 ), and hA1 j fB51 2/3 C21 1/3 gOsD51 dO4 (C Mg21 and Zn21 ) prepared by solid-state reaction technique is reported. It was found that the mixtures containing Nb51 , Ga31 , Fe31 , and As51 form the longest series of members of the KTP structural family. KTP phase formation was detected by x-ray powder diffraction analysis. Comparison of the lattice parameters measured with those known for the nonsubstituted crystals of the KTP family was carried out. The data obtained were used for the discussion of variations of KTP structural stability on composition.
I. INTRODUCTION
The physical properties of crystals with the structure of KTiOPO4 (KTP) are expected to be of great interest in the field of nonlinear optics.1–10 The structure of KTP is known2 to be constructed of a three-dimensional framework of TiO6 octahedras and PO4 tetrahedras and contain spacious channels along the c-axis. The cations of monovalent metals are located in these channels and are surrounded by eight or nine oxygen anions. Since KTP melts incongruently, the flux method is widely used for the growth of crystals with this structure. Various substitutions into the KTP structure by isovalent cations were reported. Cations of Tl1 , Rb1 , and Cs1 are known to substitute for K1 in 8–9-coordinated positions; Zr41 and Sn41 substitute for Ti41 in octahedral positions, and As51 and V51 substitute for P51 in tetrahedral positions.1–4 The isovalent substitutions mentioned were used to modify the structure and properties of KTP. There are also reports of flux growth of single crystals of the KTP family corresponding to chemical formulas of K[Nb1/2 C1/2 ]OAsO4 (C Al31 , Ga31 , Fe31 , and In31 ),5 and K[Nb2/3 C1/3 ]OAsO4 (C Mg21 and Zn21 ).6 A view of some of the above crystals grown by the procedure similar to that described in Refs. 5 and 6 is given in Fig. 1. Recently the results of K[Nb1/2 Al1/2 ]OAsO4 single crystal structural analysis were reported.7,8 Strong preferences of Nb51 and Al31 cations to occupy different
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http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 6, Jun 1999
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crystallographic sites in K[Nb1/2 Al1/2 ]OAsO4 crystals was observed. Almost all Nb51 cations were found to be located in Ti(1) sites and almost all Al31 cations were found to be located in Ti(2)
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