Using high pressure to prepare polymorphs of the Ba2Co(1-x)Zn(x)S3 (0 ≤ x ≤ 1.0) compounds.

In this work, high pressure was used as a tool to induce structural transition and prepare metastable polymorphs of ternary sulfides. Structural transformations under high pressure of compounds belonging to the Ba(2)Co(1-x)Zn(x)S(3) (0 ≤ x ≤ 1.0) series were studied using X-ray diffraction and electron microscopy. All members of the Ba(2)Co(1-x)Zn(x)S(3) series show the Ba(2)CoS(3)-type one-dimensional structure, but, after heating under pressure, the Ba(2)CoS(3) compound (x = 0) separates into BaS and the two-dimensional BaCoS(2-δ) (δ ≈ 0), while Ba(2)Co(1-x)Zn(x)S(3) compounds with x ≥ 0.25 maintain their one-dimensional features but rearrange into polymorphs showing the Ba(2)MnS(3)-type structure. All structural transformations can be linked to shortening in interchain metal-metal distances caused by the high pressure, and the role of the zinc in preventing loss of one-dimensionality is discussed.

Synthesis and characterisation of the quaternary nitride-fluoride Ce2MnN3F(2-delta).

Ce(2)MnN(3)F(2-delta) has been synthesised via low-temperature fluorination of the ternary nitride Ce(2)MnN(3). To the best of our knowledge, Ce(2)MnN(3)F(2-delta) is the first quaternary nitride-fluoride to be reported. The reaction of Ce(2)MnN(3) with 10% F(2)/N(2) at 95-115 degrees C yields the fluorinated phase Ce(2)MnN(3)F(2-delta), with tetragonal symmetry (P4/nmm a = 3.8554(4) A and c = 13.088(4) A based on neutron powder diffraction), accompanied by starting material. Rietveld refinement supports a staged fluorine insertion reaction (into alternate rocksalt layers) to give a product with stoichiometry Ce(2)MnN(3)F(2-delta). A comparison with the formation of Sr(2)TiO(3)F(2) and the isostructural LaSrMnO(4)F indicates that two F(-) anions are inserted but no F(-)/N(3-) substitution takes place. Magnetic susceptibility measurements show a transition from Pauli paramagnetic behaviour, in Ce(2)MnN(3), to paramagnetic behaviour upon fluorination. The effective magnetic moment in Ce(2)MnN(3)F(2-delta), mu(eff) = 5.38 mu(B), is consistent with an intermediate value between that of Mn(3+) (4.9 mu(B)) and Mn(2+) (5.9 mu(B)) supporting the proposed stoichiometry, Ce(2)MnN(3)F(2-delta).