Abstract
A new reduced potassium niobate (∼KNb 4O 6) of intergrowth type structure containing condensed Nb 6O 12 clusters has been found. The structure has been determined from HREM images. The atomic positions have been refined with the Rietveld technique using X-ray powder diffraction data. The space group of KNb 4O 6 is P4 mmm ; Z = 1 , and its unit cell parameters are a = 4.1393(1) and c = 8.2537(2). ∼KNb 4O 6 consists of alternating slabs of KNbO 3 (perovskite) and NbO (ordered deficient NaCl-type) both being a single unit thick. The structure is closely related to that of A 2Nb 5O 9 ( A = Ba, Sr). Both phases can be considered as members ( n = 1 and 2 respectively) of a homologous series A n Nb 3+ n O 3+3 n . Electron microscopy studies show the presence of defects, both as extra perovskite layers and missing NbO slabs, together with areas of more disordered intergrowth. The profile refinement and microanalysis of individual crystal fragments both indicate the structure to be niobium deficient according to the formula K 1+ x 2 Nb 4−x O 6 .
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