Abstract
The relation between chemical composition, crystal structure and electrical features of lead germanate, (Pb~5–x~ Ba__~x~__)Ge~3~O~11~, pure and doped with Ba (x = 0, 0.10, 0.25) was studied. The O deficiency and GeO~2~ precipitation was found in the crystals studied. In the case of the Ba‐doped crystals, the XPS lines width (FWHM) variation suggests structural local disorder. The valence band is placed near 3 eV and it shows an exponential tail, which is ascribed to existence of energy levels correlated to defects. Both the valence band edge shift and the degree of disorder deduced from the change in the XPS lines width vary non‐linearly with the concentration of the Ba ions. The ac conductivity activation energy values E~a~ = 0.55–0.85 eV indicate electric conductivity of lead germanate is determined by local energy levels originated from point defects. The analysis of the imaginary part of the electric modulus M ″(T, f) exhibited the electronic relaxation process related to electric conductivity, for which the activation energy E~M~ = 0.63–0.72 eV, and the characteristic times τ~0~ of the order of 10^–13^ s were evaluated. The crystal structure parameters and several of the electrical conduction parameters exhibit non‐monotonic dependence on the Ba concentration. It was deduced that Ba ions contributed to the mentioned phenomena by two opposite mechanisms. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)