Crystal structure and compressibility of Ba4Ru3O10

The crystal structure of Ba4Ru3O10 has been determined by single-crystal X-ray diffraction at room pressure. From refinements to R = 0.0203 at room temperature and ambient pressure, the material is orthorhombic with space group Cmca (space group No. 64) and has lattice parameters of a = 5.7762(15) Angstrom, b = 13.271(4) Angstrom, and c = 13.083(3) Angstrom. The unit cell thus has a volume of V = 1002.9(8) Angstrom(3) and contains four formula units (Z = 4), Ba4Ru3O10 is therefore of higher symmetry than the previously reported monoclinic structure based on powder X-ray data. It is isostructural with the quaternary oxides Ba-4(Ti,Pt)(3)O-10 and Ba4Ir2AlO10 and the ternary fluorides Cs4M3F10 (M = Mg, Co, Ni, Zn), Kinked chains of RuO6 octahedra run along the c direction, consisting of sets of three face-sharing units joined at the corners of the end units to additional similar sets. The two distinct Pa sites show 10-fold and Ii-fold coordination. Compressibilities and bulk modulus have been determined from lattice parameter variations at pressures up to 5.4 GPa, No phase transition was observed up to this pressure. Compressibility is greatest along the c axis and the bulk modulus obtained from a weighted fit to a Vinet equation of state is 113.3(47) GPa. (C) 2000 Academic Press.