Crystal structure and physical properties of BiCoPO5

BiCoPO5 is isostructural with BiNiPO5, a = 7.253(1) Angstrom, b = 11.294(1) Angstrom, c = 5.230(1) Angstrom, beta = 107.82(1)degrees, P2(1)/n, z = 4, R-1 [I > 2 sigma(I)] = 0.025, R-1 for all reflections = 0.030, Co is in a s lightly distorted octahedral coordination with Co-O bonds ranging from 2.00 7(5) to 2.150(5) Angstrom. Pi is in six-fold coordination to oxygen in a di storted octahedral coordination with Bi-O bonds ranging from 2.129(4) to 2. 693(5) Angstrom. The lone-pair electrons are 0.39 Angstrom from the Pi nucl eus. The PO, tetrahedron is quite regular with P-O bonds 1.532(5)-1.558(5) Angstrom. Phases in the solid solution series BiNi1-xCoxPO5, 0 less than or equal to x less than or equal to 1 are monoclinic, Magnetic susceptibility measurements show that they are all antiferromagnets with T-N varying from 20 K for the pure Ni phase to 15 K for pure Co. The materials are semicond uctors with E-g = 0.38 ev and E-g = 0.9 ev for the Ni and Co compounds, res pectively. When monoclinic BiCoPO5 is heated past the melting point to 950 degrees C it decomposes and an orthorhombic phase is formed. Single crystal Weissenberg photographs of this new phase yield lattice parameters a = 14. 688(3) Angstrom, b = 11.229(2) Angstrom, c = 5.438(1) Angstrom, space group Ibam or Iba2, (C) 1999 Academic Press.