Synthesis, structure and properties of layered bismuthates: (Ba,K)3Bi2O7 and (Ba,K)2BiO4

The synthesis, structure and properties of the layered bismithates, (Ba,K)2BiO4 and (Ba,K)3Bi2O7, are reported. These compounds, synthesised at low temperature in closed vessels, are the first and second members of the Ruddlesden–Popper series, Ban+1(Pb1−xBix)nO3n+1. (Ba,K)3Bi2O7 exhibits a semiconductor-like behaviour at low temperature. No superconducting transition is observed in any of these phases. The compounds crystallise in the I-centred unit cell, and Rietveld refinement based on X-ray diffraction data revealed the buckling of the BiO2 plane for (Ba,K)3Bi2O7, which can be a reason for the absence of superconductivity. However, this cell buckling and partial ordering of the Ba- and K-cations are absent in the (Ba,K)2BiO4 structure, that makes the n=1 member, containing an isolated (BiO2)-layer, promising for further search of superconductivity among layered bismuthates.