STRUCTURAL EVOLUTIONS IN THE SR1-XBAXZRSE3 SERIES

Compounds in the Sr1-xBaxZrSe3 series, where 0 less than or equal to x less than or equal to 0.68, were prepared from SrSe, BaSe, Zr, and Se in evacuated and sealed silica ampules, at temperatures between 900 a nd 950 degrees C. An amorphous Zr-Se phase is competitively formed in the reaction thus synthesis mixtures require 20 and 40% mole excess of Zr and Se, respectively. The Sr1-xBaxZrSe3 compounds adopt the NH4CdC l3 structure type, containing columns of double edge-sharing ZrSe6 oct ahedra linked by distorted (Sr,Ba)Se-9 tricapped trigonal prisms. For 0.68 < x < 1.0, biphasic mixtures of CsNiCl3- and NH4CdCl3-type compou nds are obtained. The x approximate to 1.0 phase is a commensurate mis matched chain compound of formula Ba1.07ZrSr3. The (Sr,Ba)Se-9 tricapp ed prisms show a marked decrease in bond distance anisotropy as the Ba 2+ concentration increases in the Sr1-xBaxZrSe3 series. The structure of SrZrSe3 was determined from Rietveld profile analysis of the powder X-ray diffraction data whereas Sr0.74Ba0.26ZrSe3 and Sr0.32Ba0.68ZrSe 3 were structurally characterized from single crystal X-ray studies. C rystallographic data for: (293 K)-orthorhombic, space group Pnma, a = 8.915(1), b = 3.965(1), and c = 14.514(2) Angstrom, V = 513.1(1) Angst rom(3), Z = 4, R = 5.39%, and R-wp = 6.55%; Sr0.74Ba0.26ZrSe3 (293 K)- orthorhombic, space group Pnma, a = 8.9305(2), b = 3.9796(13), and c = 14.611(2) Angstrom, V = 519.3(2) Angstrom(3), Z = 4, R(F-0) = 3.04%, wR(F-0(2)) = 5.95%; Sr0.32Ba0.68ZrSe3 (293 K)-orthorhombic, space grou p Pnma, a = 8.974(11), b = 4.0065(4), and c = 14.7868(12) Angstrom, V = 531.66(9) Angstrom(3), Z = 4, R(F-0) = 4.12%, wR(F-0(2)) = 9.94%. (C ) 1997 Academic Press.