American Chemical Society
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2D−3D Transformation of Layered Perovskites through Metathesis:  Synthesis of New Quadruple Perovskites A2La2CuTi3O12 (A = Sr, Ca)

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journal contribution
posted on 2004-03-22, 00:00 authored by T. Sivakumar, K. Ramesha, S. E. Lofland, K. V. Ramanujachary, G. N. Subbanna, J. Gopalakrishnan
We describe the synthesis of two new quadruple perovskites, Sr2La2CuTi3O12 (I) and Ca2La2CuTi3O12 (II), by solid-state metathesis reaction between K2La2Ti3O10 and A2CuO2Cl2 (A = Sr, Ca). I is formed at 920 °C/12 h, and II, at 750 °C/24 h. Both the oxides crystallize in a tetragonal (P4/mmm) quadruple perovskite structure (a = 3.9098(2) and c = 15.794(1) Å for I; a = 3.8729(5) and c = 15.689(2) Å 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 CuO4/2O2/2 sheets alternating with triple octahedral Ti3O18/2 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 μB for I and 0.0033 μB 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 K2La2Ti3O10 and Ca2CuO2Cl2 follows a different route at 650 °C, K2La2Ti3O10 + Ca2CuO2Cl2 → CaLa2Ti3O10 + CaCuO2 + 2KCl, revealing multiple reaction pathways for metathesis reactions.