title: 2D-3D transformation of layered perovskites through metathesis: synthesis of new quadruple perovskites A2La2CuTi3O12 (A = Sr, Ca).
abstract: We describe the synthesis of two new quadruple perovskites, Sr(2)La(2)CuTi(3)O(12) (I) and Ca(2)La(2)CuTi(3)O(12) (II), by solid-state metathesis reaction between K(2)La(2)Ti(3)O(10) and A(2)CuO(2)Cl(2) (A = Sr, Ca). I is formed at 920 degrees C/12 h, and II, at 750 degrees C/24 h. Both the oxides crystallize in a tetragonal (P4/mmm) quadruple perovskite structure (a = 3.9098(2) and c = 15.794(1) A for I; a = 3.8729(5) and c = 15.689(2) A for II). We have determined the structures of I and II by Rietveld refinement of powder XRD data. The structure consists of perovskite-like octahedral CuO(4/2)O(2/2) sheets alternating with triple octahedral Ti(3)O(18/2) sheets along the c-direction. The refinement shows La/A disorder but no Cu/Ti disorder in the structure. The new cuprates show low magnetization (0.0065 micro(B) for I and 0.0033 micro(B) for II) suggesting that the Cu(II) spins are in an antiferromagnetically ordered state. Both I and II transform at high temperatures to 3D perovskites where La/Sr and Cu/Ti are disordered, suggesting that I and II are metastable phases having been formed in the low-temperature metathesis reaction. Interestingly, the reaction between K(2)La(2)Ti(3)O(10) and Ca(2)CuO(2)Cl(2) follows a different route at 650 degrees C, K(2)La(2)Ti(3)O(10) + Ca(2)CuO(2)Cl(2) --> CaLa(2)Ti(3)O(10) + CaCuO(2) + 2KCl, revealing multiple reaction pathways for metathesis reactions.
authors.affiliation: Solid State and Structural Chemistry Unit, Materials Research Centre, Indian Institute of Science, Bangalore-560 012, India.
authors.forename: T
authors.initials: T
authors.lastname: Sivakumar
authors.forename: K
authors.initials: K
authors.lastname: Ramesha
authors.forename: S E
authors.initials: SE
authors.lastname: Lofland
authors.forename: K V
authors.initials: KV
authors.lastname: Ramanujachary
authors.forename: G N
authors.initials: GN
authors.lastname: Subbanna
authors.forename: J
authors.initials: J
authors.lastname: Gopalakrishnan