Effect of fluorine on terrace-ledge-kink morphology and valence state of copper and titanium ions in CaCu3Ti4O12

Ceramic CaCu3Ti4O12 (& Scy;& Scy;& Tcy;& Ocy;), Ca0.98Cu3Ti4O11.96F0.04 (C Delta CTOF), and CaCu3Ti4O11.92F0.08 (CCTOF) were synthesized by the solid-state reaction technique. Fluorine stimulates the formation of Cu-depleted grains, Cu3+ ions, and Cu-rich composites CuO-xCCTO-yTiO(2)-zSiO(2)-w & Scy;aF(2) (w < z < y < x < 1), which include parts of grinding bodies. The observed structures are distinct from simple grain boundaries of the perovskite phase. They exhibit a terrace-ledge-kink (TLK) morphology and, in some cases, the presence of twinning planes, both independent of fluorine content. They are responsible for the nanoscale barrier layer capacitance (NBLC) component of the dielectric response of both CCTO and CuO ceramics. Changes in the unit cell parameter a, and titanium and copper valences indicate that Ca2+ ions occupy part of Cu vacancies in the grains of CCTO and CCTOF. In C Delta CTOF, Ti3+ ions in the copper sublattice were found for the first time using NMR. The maximum epsilon '(1kHz) = 6.9 x 10(4) demonstrates C Delta CTOF and the minimum tan delta = 0.045 is characteristic of CCTOF.