In this paper we report the phase relations of the tetragonal tungsten bronze type strontium barium niobate (SrxBa1-xNb2O6) solid solution in the temperature range from 1200degreesC to 1450degreesC. The x-value depends on the synthesis temperature and reaches from 0.19 less than or equal to x less than or equal to 0.62 at 1200degreesC up to 0.18 less than or equal to x less than or equal to 0.84 at 1440degreesC. In addition lattice parameters of the stable phases at 1300degreesC depending on their chemical compositions are given. Samples with different SrO:BaO:Nb2O5 ratios were sintered in vertical tube furnaces at suitable temperatures in air. The chemical composition of the quenched equilibrated phase associations were determined by EPMA. Lattice parameters of the resulting crystalline phases were derived from refinement of d-values from XRD patterns. The phase field of SBN is strongly temperature dependent. The Ba-rich end-member of the solid solution contains 80 mol% Ba and 20 mol% Sr independently of the synthesis temperature. On the other hand the maximum Sr-content of the solid solution increases with temperature from 62 mol% Sr at 1200degreesC up to 84 mol% Sr at 1450degreesC. Also the Nb-content varies with temperature especially at synthesis temperatures below 1400degreesC. In particular at 1300degreesC the solid solution field of SBN extents to higher Nb-contents on the Ba-rich side leading to a Sr-free end-member of the solid solution. For this Ba-rich side of the solid solution series a substitutional formula Ba4Sr(1-y)Nb(y)Nb(10)O(30+ 1.5y) (0 less than or equal to y less than or equal to 1) can be given. A new compound (Sr, Ba)(5)Nb8O25 in the SrO-BaO-Nb2O5 system has been found, exhibiting also a solid solution range. Chemical compositions of some previously described phases could be determined in more detail. The lattice parameters of the tetragonal tungsten bronze cell (Al(2)A2(4)C(4)M1(2)M2(8)O(30)) depend on the chemical composition of the solid solution. In the Sr-rich region and at low Nb-contents the a-parameter shifts strongly while on the Ba-rich side and at high Nb-contents the variation is lower. The c-parameter increases with the Ba-content. (C) 2004 Elsevier B.V. All rights reserved.