Abstract Columbite ceramics A 1–x Nb 2 O 6 (where A = Mg, Co, Zn and x = 0, ‐0.005, ‐0.01, ‐0.03, ‐0.04) were studied by means of positron annihilation spectroscopy. The lifetime spectra revealed the presence of two lifetime components. The first component originates from positron annihilation inside of the grains. The second component is due to annihilations in the grain boundary regions. From the intensity of the second component and simulations (C. Hübner, T. Staab, and R. Krause‐Rehberg, Appl. Phys A 61 , 203 (1995) [1]) the diameter of the grains is estimated as 2‐5 μm, ∼ 10 μm and 5‐7 μm, respectively for Mg‐, Co‐, and Zn‐containing columbites, in agreement with the results of microscopy measurements. In order to facilitate explanation of experimental results, theoretical calculations were conducted on columbite samples. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
