Synthesis, Structure, and Dielectric Properties of (Bi1/2Ag1/2)TiO3

The compound Bi 1/2 Ag 1/2 TiO 3 has been synthesized, for the first time, at 14−14.5 GPa and 1000 °C using the uniaxial split sphere anvil type press (USSA-2000). The structure of the quenched powder sample was refined from synchrotron X-ray diffraction data using the Rietveld method. At room temperature, Bi 1/2 Ag 1/2 TiO 3 exhibits an orthorhombic distortion of the cubic perovskite structure and was assigned to a space group of Ibam and lattice parameters of a = 5.48970(4) Å, b = 5.51954(5) Å, and c = 7.77585(7) Å. The refinements are consistent with a random distribution of Bi 3+ and Ag + on the A-sites. Diffraction results at various temperatures show two phase transitions as the temperature is increased. At 573 K, tetragonal symmetry is observed and was assigned to a space group of I 4 /mcm with lattice parameters of a = 5.51664(8) Å and c = 7.8134(2) Å, while at 673 K, the cubic perovskite structure, with space group Pm 3̄ m and a = 3.90607(8) Å, was determined. Plane capacitor dielectric contact measurements at 100 kHz gave a dielectric constant of 354 at ambient temperature for the sample. The dielectric constant increases with temperature and reaches a local maximum of 834 at 578 K. After heating the sample to 778 K and cooling back to room-temperature, both dielectric and diffraction measurements provide evidence for a small but irreversible change in the stoichiometry.